Daily energy expenditure through the human life course | Hacker News Reader

Daily energy expenditure through the human life course

research.brighton.ac.uk

247 pointsshartshooter239 comments

I've always been curious about my own metabolism. When I was a teenaeger / in university I ate pretty badly. Chocolate bars every day after lunch, loads of carbs, not to mention alcohol, etc etc. I was rail thin. I once got a body fat assesment when I joined a gym (I did no exercise at all and this was a brief attempt to get buff) and the person doing the test was shocked and couldn't pinch anything to measure. I had no fat. This lasted till I was 25 where seemingly overnight I then had to watch what I eat or I started to gain fat. So what explains this seeming inability to gain weight no matter what I ate, and in my mid twenties having a more normal response to junk food?

How much "passive activity" were we doing back in the day?

So as a teenager, I was carrying 5-10kg of books and walking back and forth between classes every 40 mins.

As an undergrad I was travelling across campus multiple times a day, spent hours on my feet in labs, did multiple heavy grocery shuttles and also spent a lot of time partying.

In my first job, I was still getting up 5-6 times a day for meetings and had a decent walk/cycle built into the commute. but in my first remote job, I could be sat in the same spot for 8-10 hours without moving. And because I wasn't drinking water I wouldn't need to go to the bathroom... /facepalm I'd also be so engrossed that sometimes I'd forget to turn on the lights...

So even though I do more than an hour of intense exercise a day, my activity outside of those exercise hours has cratered from when I was a teenager and was constantly running around.

So as a teenager, I was carrying 5-10kg of books and walking back and forth between classes every 40 mins.

As an undergrad I was travelling across campus multiple times a day, spent hours on my feet in labs, did multiple heavy grocery shuttles and also spent a lot of time partying.

In my first job, I could be sat in the same spot for 8-10 hours without moving.

A year in to my first job I had added 15kg (~30lbs ~2stone) - while consuming way less food and alcohol than my university days.

I actually lost weight upon entering college because my campus was so large that my physical activity increased from when I was in high school.

I understand that as a healthy body sustains lifestyle damage, the effects begin to stack up, and then the effects become more noticeable, but it's not age based because it's reversible.

So look to your unhealthy lifestyle's accumulated effects in your body, atherosclerosis, obesity, pre-diabetes, hypertension, specific nutritional deficiencies, physiological mental health... And make a robust effort to improve your lifestyle, and you'll start to feel like you did, 10, 20 years ago.

Speaking from personal experience, I'm 50ish and after getting a health scare which triggered me into aggressive corrective action a few years back, I've overcorrected. My allergies have ameliorated back to old levels, I can drink beer again, and I can recover from a night out like I used to be able to in my 20's, I'm able to maintain a serious athletic schedule. Obviously most of the time I now eat really well, but my body's youthful tolerance to harm has been recovered.

Would love to hear what sort of things you did as part of your intervention?

Def noticing amongst my friends a few new allergies/intolerences manifesting as we get older

For some context am reasonably healthy and actually had to increase my sodium intake because I had over corrected on reducing salt consumption and was getting hyponatremic after training

A good story is Rich Roll’s Finding Ultra. Or a good technical read on nutrition is Julia Ross’s The Mood Cure. But I read about 50 non fiction books cover to cover each year, and learning about your health is a big area, made harder by the reality that for every good book on the topic there are 19 others that are bad. There are lots of bad fads and actors, and they can include pill pushing doctors, sadly. The only real way to figure out how to get healthy is to experiment until you succeed at it. I guess one piece of specific advice I’d give, is if you have long term high cholesterol, and high blood pressure, take your doctor’s advice and take a statin if they recommend it. I think that was a huge boost. Also, when you want online advice on health, add ‘site:.gov’ to your search so that you get good sources and not health blogs.

Ultimately I think you’ve got to come up with a good model of your physiology based on uncontroversial science. So in the case of your training, you’d figure out you are draining yourself of more than sodium chloride but rather the broad spectrum of minerals that you typically sweat out, so your ‘salt intake’ is a multi mineral supplement and not actual salt. Which is what I imagine you figured out.

In addition to activity levels, you probably just weren't eating that much food. It was similar for me when I was a teenager: some days I would binge on a ton of junk food, but other days I would forget to eat breakfast, and the latter happened often enough that I stayed skinny.

No I legit ate way much much more in my 20s. I'm not misremembering. I ate more

I had to supplement with calorie shakes for workout guys in my 20's, just to maintain weight. I ate trash, and a shit load of it. And that's not considering the amazing levels of calories I would've consumed from alcohol.

Same activity level now as then. But now if I think too hard about a candy bar I gain weight that never goes away.

> Same activity level now as then.

As you go from untrained to trained you burn less calories doing the same activity.

It's actually nowhere near as simple as that, and it depends on how you define the "same activity".

Moving your body from one location to another at a particular speed results in a fairly static amount of work done (in the basic physics sense). So if the same you hops on a bicycle and cycles up the same hill in the same conditions with the only difference being that one of you has trained hard for the last 5 years and the other hasn't (but somehow your body mass has stayed the same) then you'll burn exactly the same amount of energy. Untrained you will find it much harder, but the energy burn will be roughly the same.

There are some things that can be different as you go from "untrained" to "trained", for example lighter people burn less energy moving themselves around than heavier people. Trained people tend to do activities harder/faster so the "same activity" could actually be a much harder activity despite it not feeling that way. Although if the activity involves travelling a set distance some of the extra effort involved in doing it faster is offset by the fact that it takes less time, so the difference between the two is not as large as you'd think.

same here. the hockey-stick or v-shaped weight rebound if I even deviate a tiny bit. amazing how fast weight comes back on.

>I'm not misremembering

It's the easiest explanation. As a gym bro that regularly cycles weight, it's is remarkably easy over/under estimate intake just going off recollection. I always think I'm dialed in until I write things down (I'm almost always eating way fewer calories than I think).

Okay, so just to be clear: the OP is describing a phenomenon that is extremely widely reported, and is doing so in discussion thread about study that also reports finding this phenomenon, and your claim is that the simplest explanation is that OP is misremembering, and the research is just wrong?

Do you have any evidence for this bizarre dismissal?

The study says that TDEE is generally constant from 20 to 60. Multiple studies have shown that on average people do a terrible job of estimating their food intake ([1], [2] for example), especially when they aren't actively monitoring it. Meanwhile the person you're talking about (who isn't properly "OP") is claiming that they ate more in their 20s than they do today without corresponding health effects. This is not consistent with TFA nor with previous research.

1: https://www.nejm.org/doi/full/10.1056/nejm199212313272701

2: https://www.tandfonline.com/doi/abs/10.1080/08870446.2019.16...

(This thread is now hella old, but only look at comments every once and awhile, thus the late reply).

I'll just say the same thing I always say in these kinds of "who are you to deny science!?" replies. For everyone championing how hard, complex, and subtle weight loss is, there's a "dumb" gym bro just weighing him self every day and dialing back calories until the scale starts going in the right direction. It works every single time. 100% of the time.

I don't understand where does the excess basal energy expenditure go. Do persons like the OP when <25 y.o. produce significantly more heat (e.g. wearing only t-shirt and shorts even in winter, and "dying" in the summer)? Does the skinnier body mean way bigger heat losses, even when compared to bigger surface area after getting fat (i.e., way higher surface temperature)? (presumably yes, but to this extent?) The article states that the basal expenditure increases with "fat free mass", so someone fat but muscular will have this "overheating" problem even stronger?

one possible explanation for me, calories ingested != caloric intake. I ate more, pooped more. So even if my body's metabolic efficiency didn't change, perhaps my ability to extract calories from what i ate changed.

Sitting down and eating 6 plates of pasta at Fazolis all-you-can-eat for $4 (or $6) + 12 breadsticks every wednesday evening, is not something you can misremember. i was a broke student, and it was most economic meal i used to have. Working at mcdonalds and eating double quarter pounder meal + extra quarter pounder + shake is not something i can misremember. clearing a tub (not a pint) of ice-cream at a sitting is not something i can misremember. setting timer to dliberately eat 6 times a day all summer in order to forcefully gain wait, is not something i misremember. emptying an entire box of cereal in a sitting is not something i misremember. Eating 25 big wings to the bone at a sitting is not something i misremember. And i was all of 130lbs max. It really is insulting to suggest that the likely explanation is that I am misremembering.

In my 40s now, eating a lot is day like today when all I ate was jamaican takeout that i ate most of it. and that's on the high end of what i usually eat. i strictly drink water and black coffee, nothing else. my entire 20s was pop and juice. thats easily another 400 calories daily. I am 150lbs now.

I believe you, naijaboiler.

Posts like Jenda's are depressingly unimaginative.

I wish HNers, and people in general, would learn some biology, and use some critical thinking to imagine that when something doesn't fit their very basic mental model, that's probably because there's exponentially more to know/learn(!). Maybe then they would stop thoughtlessly regurgitating such basic misconceptions.

Biology has so much complexity, but so many people want to insist calories in MUST balance calories out, without any exceptions. As if humans are just burning our foods at 100% efficiency in a bomb calorimiter. Biology isn't this boring.

Forgetting digestion and a host of other variably efficient processes, Mitochondria produce ATP from various possible substrates. These substrates are not equally efficient at producing ATP. So just here, in the simplest form, you have a mechanism by which input energy can be wasted or conserved.

Separately, when demand for ATP has suddenly ceased, Mitochondria can change modes to deterministically waste huge amounts of energy to avoid over-producing ROS. So even in the same cell, even provided the same substrates, efficiently can be dialed up and down rapidly.

And we haven't dug deeply into anything. There are so incredibly many processes with highly variable efficiency.

There's much more that we have yet to learn than that we know. Don't underestimate the complexity of biology.

> Posts like Jenda's are depressingly unimaginative. I wish HNers, and people in general, would learn some biology, and use some critical thinking to imagine that when something doesn't fit their very basic mental model, that's probably because there's exponentially more to know/learn(!).

That's why I was not disputing the premise (like previous commenters did), but asking for possible explanations!

I apologize, you're right - you were sincerely questioning "where does the energy go?" - which is laudible. I mistakenly read your post as insincere and lumped you in with the others who were being dismissive. I should have directed my criticism at grandparent posters.

There's definitely a heat-loss phenomenon - look for skinny kids in shorts in 40 degree weather - but it's also the case that a variable amount of input calories can be discarded without full digestion by the body - energy not even extracted for use. The religiously calories in : calories out folks assume a linear digestion efficiency relationship between total calories consumed and that this holds unifomally across the population. Given the complexity of biology, they should be unsurprised that there will be myriad outliers

this. Yes the physics of weight is ridiculously straight forward. Its first law of thermo (calories in = calories out). The biology is incredibly complex and that's before we get to the pyschological, to the point of making CICO too overly simplistic to describe actual practical reality. The body is not some perfect energy converting mechanical machine.

People also forget "metabolism doesn't change with age" narrative is a based on a paper that used population-wide statistical model. That approach measures "average treatment effect" and is directionally useful in general but incredibly unhelpful in addressing individual differences and nuances. Something is true on average does not mean it is true "for every" or even "for any"

Skinnier would mean more surface area to volume, but less surface area total.

If we're just looking at energy in and energy out, it could partly be less thorough digestion. I wonder if there are poop studies that find more leftover fat or carbs in faeces of children.

Yes - for example: overconsume fat to an extreme degree and watch the color of your stool turn towards white/clay, and watch it start to float, among other notable changes (size, shape, consistency, odor, etc.)

I was rake thin until I started lifting weights with a buddy of mine at university. However it wasn't until I started GOMAD that I noticed any muscle and weight gain.

Before that I was eating crap. Lots of things that I that were high in calories but not enough of them throughout the day to exceed my metabolism or get close to the amount of protein I needed.

I think if you could go back in time and count the calories you probably were eating as much as you think.

Maybe lifting weights => Body actually uses and stores all food => Fat at 40?

Whereas a thin man who doesn’t do sports never gets really fat?

N=1, but visceral fat starts building up sometime after age 40 anyway. About 52, in my case.

Yeah, but likely you walked more. Cycled more. Ran more. Stuff like that.

activity levels almost certainly. uni it's not impossible you were walking over 12k steps a day. that's 3-400 calories over the average american's daily steps of 4000.

That's also completely canceled out by enjoying a single 32oz soda. Walking a lot and having a bad diet rarely even each other out. And it's so easy to cancel it out I don't think most people realize. A brisk 2km walk burns less calories than are consumed when eating two regular Oreos.

I wouldn’t be surprised if most thin people who claim to eat lots of junk food actually just eat a lot less regular food. In other words, they don’t eat many calories, but the calories they do eat are junk.

This. Plenty of times I've been to lazy to make dinner and ate 200g of chocolate and a coke in a single sitting.

I assume you mean a bar mostly consisting of dairy and sugar with a bit of chocolate -- making a meal out of actual high quality dark chocolate adds up, but can hardly be considered junk food. <3 my 90% dark Lindt chocolate bars -- between those and all the bacon I've been eating this year the pounds are falling off.

The American dream

Pretty sure if it was the American dream, it would be 7oz of chocolate.

I believe for this to be the American dream, you have to do this in addition to dinner.

I would say this was partially true in my case. While I ate badly, I didn't eat huge portions regularly. I also didn't eat breakfast regularly then (and often don't now either). In college we got fish and chips takeaway once it twice a week,and while it was definitely the worst kind of junk, I would be full quicker than others. That said, I regularly put away a quarter pointer, portion of chips, fizzy drink and a cheese and onion pie (deep fried cheese basically, and amazing). And not an ounce of fat on my body.

Strava tells me I burned 3,3000 calories this morning on my (4 hour)100km bike ride. About the equivalent of drinking 2 cups of melted butter, or eating 50 pounds of lettuce. When I'm doing exercise like that regularly it's hard to eat enough.

Strava’s calorie estimation is awful.

Depends on the elevation gains in your 100km ride but I think that 3,300kcal for a 100km/4h ride is generous.

800kcal/hr is hard work and keeping that up for 4h is even harder. 25kph does not sound like 800kcal/hr unless there was some reasonable elevation gains. I’d expect at least 1000m elevation gain over that 100km for those numbers to at least approach something sensible. If it was a flatter ride than that then Strava is just lying to you.

But, yes, long distance cycling is an awesome way of burning calories. When I used to do Brevet/Audax riding I was the closest to my old teenage weight as I have been in the last ~30 years.

Yeah, 25km/h requires less than 150W [1], so it's 600Wh total, the efficiency of human metabolism is about 20% [2], so it's 3kWh of total energy input = 10.8MJ = 2600 kcal. (I have been using generous estimates, so this should be an upper bound)

[1] https://en.wikipedia.org/wiki/Bicycle_performance#Total_powe..., https://www.road-bike.co.uk/articles/cycling-power.php [2] https://www.quora.com/How-efficient-is-the-human-body-at-con...

Given that we're talking about cycling, the solution is to buy a power meter and measure rather than estimate. Unfortunately that's a rather expensive option for all but the most committed cyclists.

Being someone who has a power meter, I can say that strava's estimates over a long time period aren't that terrible, but if you're riding in a group, or there was a some wind, or a million other reasons they can be absolutely miles out.

That's hardly strava's fault, it's more about what's actually possible with an estimate.

What is completely made up and should be ignored is the calorie burn estimates you get from gym equipment.

    Strava’s calorie estimation is awful.

Re-reading your post made me think: I bet this is intentional design -- overestimate number of calories burned. Then, people will tell their friends about this amazing device from Strava that burns an unreasonable number of calories...

I am also very skeptical of Strava's caloric estimates but:

> I’d expect at least 1000m elevation gain over that 100km

1% average grade is pretty mild. I'd bet OP did at least 3000m to get those numbers

It’s 2% average grade if you finish at the same elevation as you start.

That’s more than an order of magnitude more calories burned than walking 12k steps.

Humblebrag? Almost 100% of humans are incapable of doing a four hour 100km bike ride without a lot of prep and training. Nevermind doing this daily.

A person who gets their doctor recommended 150 minutes of moderate aerobic activity each week shouldn't have much difficulty adapting their bodies to distance cycling well enough to hit comparable numbers after a handful of training rides. Elites can hold pace for those distances at 50 km/hr, which is faster than me doing an all-out sprint.

And one doesn't have to do 100km all at once. A 10km commute each way over a 5 day workweek is a much less intimidating prospect.

When I lived in Denmark I was riding 2x 5km to and from work. I then needed to start going somewhere ~80km away, and I was able to do it without special preparation. After a couple of times I was able to do it both ways in a day.

Now I live in America need a car :(

I also did a 65km and then 135km ride with similar "training" (2x7km four times a week to school), but it was way slower than 25km/h. They took 4.5 and 10 hours, respectively. I think riding 100km without training is possible, but at 25km/h very difficult.

> Now I live in America need a car :(

Why? Are there even longer distances?

No, there's just no cycling infrastructure.

I was doing it on a roadbike and could comfortably average 27km which got me there 3h. Driving was about 1.2h.

In the summer, I would start pedalling at 5am and get to a local cafe at 8. The first hour was amazing, broad daylight and you basically had the whole road network to myself.

There is almost none here (around Prague, .cz) too. I ride on the roads.

Yeah, unfortunately, for me, even after some training, it's still hard for me to average over 22 km/h (entire travel including stops; the moving average is about 25km/h, e.g. https://www.strava.com/activities/9688833121).

Why did you leave Denmark? A job? University? That sounds like a terrible trade for quality of life, including raising a family.

Honest question, are you asking as someone who has experienced living in Denmark or a similar country? It is indeed a good place to live for the median person. But if you're a high achiever, it's a fact of life that the opportunity is in the US.

I think the numbers are more than you'd think - as a cyclist who's near the top end of "keen amateur" but still nowhere near what people are capable of at the elite level my experience is that anyone of moderate fitness can do a 4 hour 100k without too much trouble...

It could depend on how you define "almost 100%" of course. There's a big difference between 5% and 0.001%.

While true, the energy expense doesn't really scale with speed, so if a couch potato got up and decided to do 100k in, say, 8 hours, that's around the same amount of energy.

NB nobody would be able to do this without ingesting a substantial amount of food during. If you didn't start eating hourly after about 1-2 hours in, you'll "bonk" or run out of glycogen.

It really depends on how fat adapted your metabolism is. When untrained people exert themselves their muscles tend to produce most energy from glucose and very little from fat. By doing a lot of zone 1-2 training you can gradually shift your metabolism to rely more on fat, at least at lower effort levels where you're not limited by oxygen. This allows you to go longer than 2 hours without bonking.

It does depend on your conditioning though. When I did my first 200km ride I ate like a horse every 50km.

After a few years of regular (monthly) 200km rides I could do a 200km ride (~10h elapsed) without eating anything on the way round.

A lot of people could get there with like six months of not that crazy training.

Cycling at 15mph on flat ground is pretty easy. If you can do that for an hour, and can progress at 10% increase in riding time week over week (pretty reasonable for someone who is still gaining fitness from "nothing"), you'll be doing four hour rides after just 16 weeks.

I would categorize 16 weeks of training as a lot of prep

I wouldn't - sixteen weeks is just about 1% of the 30 years you have between ages 20 and 50.

that said, ok, 15mph is not that easy -- maybe starting more like 10mph on a road bike for an hour would be more reasonable.

I still think most able bodied people could get to OP's fitness in much less than a year.

One data point - I was horribly out of shape in my mid 20s and got to riding 4 hour/15mph about four months after I bought my bike. But I was also unemployed for about a month of that!

Strava is probably wrong. Even if it's right, it's not like this can continue forever. At some point, the weight loss will stop despite Strava showing a deficit. So either you have to eat less or exercise even more.

25km/h is the regulatory max speed of e-bikes around here and you averaged that. Most people would take years of training to get to the point of being able to exercise like this.

Really depends on the bike. It's way easier to achieve this on a racing bike than on a trekking/city/mtb

no, they wouldn't

While this is certainly an argument for “how do I lose weight” the relevant part here is that the asker wondered why they started gaining weight, which makes a reduction in daily calorie burn relevant if caloric intake remained roughly consistent. That is a lot of ifs, naturally.

Could be a reduction in calorie excrement really - i.e. they just started absorbing more of it.

Could be any of a number of factors. No way to know.

32oz is a ton of soda tho.. Even when I was a teen at 6'4", 32oz of soda would be a sickening addition to a meal.

Perhaps you're not American, but Gallup reports that among those who drink soda in the USA the average daily amount is 31.2 oz

32 oz, if I'm converting correctly, is a little shy of 1 liter. If so, that isn't a big amount really, especially daily.

> among those who drink soda > average

Two factors in your statement that lead me to believe 32oz is still a boat load. What's median and 75th percentile? I imagine the distribution here is non linear across the soda drinking population.

Depends how it's measured.

16oz of store-bought soda is not the same as 16oz of restaurant soda, at least 30% of which would be ice.

I wouldn't trust Gallup to report with nuance.

Thats so gross

If you think drinking a litre of soda is no big deal I would encourage you to rethink. 400 calories with no nutrition is a lot.

It is even worse than that. The conversion rate of activity to net calorie loss is not 1 to 1 . It can be zero or even negative, at least based on my own experience and other people. You see people on Reddit subs do 10k steps and tons of walking, hardly lose any weight. It's all about not overeating.

Walking is great for many reasons, but 10K steps isn't much. It would be silly to expect much weight loss from that. And most people significantly understand their caloric intake.

One of the problems is people naturally adjust their activity levels after exercise. After a two hour bike ride they will spend the evening on the sofa. It seems we naturally adjust without consciously thinking about it.

As a student, I used a bus to get to school. As an adult, I walk by foot, more than an hour a day. Also, I didn't exercise in my youth, and I do now. Yet, it is now that I am fat.

I wonder about the same thing. I was a fat kid, but my best friend was so skinny. We would walk down town and he would stop several times to stuff chocolate bars in his mouth, and then buy two McDonald's meals. I would do none of this and our physical exercise was the same.

Then we went away to University and in his mid-20s the poor guy suddenly, almost overnight, put on a ton of weight.

25 is about the age you’ve worked a year two after an undergrad. More money means more desk work and more access (speaking funds) to eat out

I had a similar trajectory. The transition from one to the other was a long course of antibiotics.

Muscle burns more energy than fat. As people age, their muscle mass declines without sufficient exercise, so we'd naturally expect the average person's metabolism to decline via this even if "metabolism per kg muscle" didn't change.

In the paper they say that the daily energy expenditure matches well a function of the fat-free mass (a power-law function, at high masses the energy per mass ratio is lower than at low masses).

Therefore all their data is based only on fat-free mass, i.e. total body mass minus fat mass.

So all their conclusions are not influenced by the amount of fat vs. muscle.

But on the other hand, adding either muscle or fat burns more energy period, and we watch the average person's weight gain somewhere between 10 and 20 pounds over the first half of adulthood.

So we could easily expect the average person's metabolism to increase as well, simply to support the extra body mass regardless of composition.

Balancing out the two effects can only really be determined through careful statistics, and is going to be extremely variable per-person.

There's good evidence that metabolic rate does vary, but not significantly.

https://examine.com/articles/does-metabolism-vary-between-tw...

The article states the difference is small, but also notes “ The majority of the population exists in a range of 200-300kcal from each other”.

All things being even 200kcal difference per day is about 20lbs per year attributed purely to metabolic difference. Now you can say to just eat 200kcal less per day, but those little differences on a daily basis add up.

> All things being even 200kcal difference per day is about 20lbs per year attributed purely to metabolic difference.

As you gain weight, you burn more energy, even just being idle, so 200kcal doesn't means 20lbs per year (obviously so, as otherwise you'd gain 600lbs in 30 years).

An extra 200kcals per day implies gaining extra weight until the extra energy you burn cancels it out, and then stabilizing there. IIRC the rule of thumb is ~25kcal/day/kg so you'd just naturally balance out to being 8kg heavier than the baseline.

> As you gain weight, you burn more energy, even just being idle

Only if you gain mostly muscle. Which I'd bet most people at a calorie surplus aren't, and the extra fat is burning very little calories.

You might become more sedentary as you gain more weight.

200-300kcal seems like an awful lot. Would the higher end of that scale, 300, apply primarily to larger men who burn alot more calories?

In the case of two small women who burnt <=2100 a day, a 300kcal difference would be the difference between one of them fasting for an entire day every single week and the other not.

That seems like a massive difference not "small".

Metabolic differences are why for a person of my height a weight of 68kg is normal but a weight of 86kg is also normal. Metabolic differences alone don't explain why many people of my height weigh 100kg and more.

totally valid point. I would expect most people to be surprised that the variance is typically smaller than a spoonful of peanut butter, but the nature of gaining or losing weight is such that even a spoonful of peanut butter over years could be the difference between many pounds of body mass.

Even better if you burn 200 more per day without feeling more hungry than someone who burns less than you

It def. adds up. To get an idea, consider cancer cachexia , which is involuntary weight loss due to cancer. Weight loss in the setting of cancer is not just due to appetite loss from side effects of treatment and sickness, but also from metabolic changes. It's such weight loss that brings the cancer to the attention of the doctor, and can be quite dramatic despite the patient not changing his or her appetite or other routine or feeling sick at all. How much of an energy deficit is this? it's believed that cachexia only causes a deficit of only 200 calories/day, but this enough to produce dramatic weight loss.

If they eat the same amount.

"Even when you’re sleeping at night, the brain consumes roughly as much energy as it does during the day."

https://www.brainfacts.org/brain-anatomy-and-function/anatom...

Does this change over time also?

I wouldn’t trust a site called BrainFacts to be unbiased given the source.

muscle burns very little calories, and even pro bodybuilders who have lots of muscle quickly put on fat off-season when not dieting. I don't think this explains it.

Muscle tissue burns 7-10 calories per pound per day. This means someone who gains 100 pounds of muscle (e.g. from 150 lbs untrained to a 250 lbs bodybuilder) would increase their metabolism by 700-1000 calories, almost a 50% increase in the average daily male calorie requirements of around 2000 calories.

Putting on 100 lbs of muscle is impossible without steroids for 99% of people even with 10-15 years of constant training.

Estimates vary but 50 lbs of lean muscle mass is generally considered the natural maximum for men.

I think 100 was just a nice round number to make their point easier to read

even with steroids virtually impossible. the heaviest pro bodybuilders ever peak at around 270-290 lbs

Someone in their first year of consistent serious training can realistically put on 15 pounds of muscle. The year after that it drops to 5 pounds.

That is an insane amount of training - big lifestyle changes!

I increased my calorific needs by 1000 a day by doing a 10K run (1hr) before breakfast.

Still a 160lb weakling :)

That seems high. Someone your weight would generally only burn about 750 kcal on that workout.

750 kcals is insanely high for a 10k training run. If you hold your HR to Z2, 620-640 kcals would be my ballpark expectation.

It’s what Strava says I’m burning so I can only go by that. 750 would still be above the low end of the range quoted by the OP.

The amount of extra food I needed to start eating!

You shouldn't go by Strava numbers, they are known to overestimate.

Fair enough but it’s still going to be at the low end of the range 700-1000 range given earlier for 100lbs of muscle gain.

I’m ~75kg. Schwarzenegger was ~120kg in his prime. 45kg difference is (2.2lbs to the kg) 100lbs (differences between UK and USA imperial notwithstanding).

The chances of me going from where I am to a AS physique is zero!

Do you have a source? I would expect the first pounds of muscle to affect metabolism more than the 100th pound, but that's my immediate intuituion.

It is essentially impossible to put on muscle at their size without also gaining fat, because they need to be in a large caloric surplus. During the off-season, pro bodybuilders are still training, they just increase their calorie intake significantly. Muscle does burn quite a few calories passively, it's just not nearly enough on a 260lb man to cover 6k-10k calorie intake.

There are multiple factors in maintaining bodyweight: diet, activity level, muscle mass, metabolism, etc. We shouldn't expect a single factor to explain everything, but holding eveything else constant, more muscle and the physical activity necessary to maintain it will burn more calories. It's an important part of maintaining health as we age.

they put on fat because the body fat level they compete at is unsustainable for long periods of time. additionally gaining fat is unavoidable when trying to gain muscle past a certain point.

I would argue they are not "gaining" fat, rather they are "balancing" the amount of fat the body considers normative. Of course you can easily acquire more fat with an inappropriate diet consisting of too much sugar, but a healthy diet will see your body maintain the ratios that are optimal for your current requirements.

It never ceases to amaze me that we think that we know better, and yet the human body, as with other animals etc, have been around for quite some time now. Even if we had all the data from the past that we think is important now, we still wouldn't know better.

There was a post the other day regarding "The prosecutors fallacy" that might fit well with this sort of subject matter.

A lot of skinny people have high metabolism, how do you explain that?

Over my life I’ve been close to a small handful of perpetually skinny people who thought they had high metabolisms. In every case, when I watched them closely, I realized they barely ate anything.

My ex-gf was one of these people and would routinely tell people about how she could eat anything and not gain weight. But when I would go on a severely calorie-restricted diet I was still eating more than she did on a normal day. I don’t think she was lying about being able to eat anything, I think she just didn’t realize how little she actually ate.

> In every case, when I watched them closely, I realized they barely ate anything

I know people (mainly Asian guys that are trying to build muscle) that seriously struggle to eat at a calorie surplus. So maybe it's not "metabolism" (which there are significant differences between humans) but also differing levels of hunger.

There is a biological feedback loop that dictates how hungry you are via hormones such as ghrelin and leptin.

My little brother is about 50lbs lighter than me at the same height and we have very different builds and all his attempts to bulk fail for the same reason: no appetite. Meanwhile I’m overshooting my bulks and have to cut harder because I love eating too much.

Eating enough food is the most exhausting part of trying to bulk. Its not hours in the gym - thats easy - its calories on the plate.

Everyone’s different.

maybe it mostly goes to the mid section. Having a large stomach but thin limbs can create the illusion of being skinny

One individual, Michael Rea, weighed (at the time of publication) 115 lbs at 6-feet and subsisted on a diet of 1900 calories a day [0], which he tracked meticulously. It's hard to convey with words how incredible this is. To put this in perspective, Ansel Key's subjects had to diet down to 1,500/day to get almost as thin. Super-fast metabolisms that cannot be explained by undereating or pathology do exist.

[0] https://nymag.com/news/features/23169/

Michael’s regimen of 1,913 calories a day is exactly that: 1,913 calories every single day, 30 percent of them derived from fat, 30 percent from protein, and 40 percent from carbohydrates. Cooking for him is the same elaborate exercise in dietary Sudoku it is for all CR die-hards, only more so.

This is more impressive than even Terrance Tao in terms of outliers...nuts. Unless you tried to lose weight of study this stuff, this is no small feat. Pro bodybuilders have to eat less than 1200/day to get super-lean and this is with tons of muscle helping. This guy does it at 1900. If there were a Tiger Woods of metabolism, this guy would be it if Tiger Woods could play better golf.

In my early to mid 20s. I had to go on intentional ingest nearly 5k a day just to gain 10 lbs. As soon I returned to my regular diet, I lost it all. In my early 40s, I dare not even eat half ass much as I did say 25, I will blow up like a balloon. My own lived experience makes me doubt the universality of that "metabolism doesn't change with age".

Maybe metabolism doesn't change, but my ability to convert what I put into my mouth into weight gain has definitely changed for me. As a young man, I used to eat way much more and poop way much more. It was like the food was just passing through, without really getting in my body. No matter how much i ate Just came right out

Why is Michael Rea considered exceptional here? For that height and weight, that's pretty much bang on what you'd expect as a maintenance level of calories assuming he does any physical activity at all.

trying to get that low of a weight would entail significant metabolic adaptation, which calculators do not account for. Take a 180lb 6-foot male and try to get him to 115 and you can be sure it will take way fewer than 1900.

The question isn’t getting there, it’s staying there.

They are master practitioners of Calorie Restriction, a diet whose central, radical premise is that the less you eat, the longer you’ll live.

It would seem like it is intentional, going by the article. They are trying to lose weight to maximize lifespan.

I’m not sure what’s in the article, I can’t read it because of a paywall, but I don’t see anywhere in the comments here discussion of Rea losing more weight, it just says he eats 1900 and he’s 6’ 115lbs.

Was he sedentary, or did he run 10 miles a day? I see no reason to believe his metabolism was unusual without more information about his physical activities.

Michael can stand up in the morning, let alone jog twenty miles a week. But jog he does, and if the results of both his latest physical and the latest CR research are anything to go by

This is 3 miles/day. not that much. Minnesota starvation experiment subjects had to walk 22 miles/week.

I just spent the last six months dieting down to 6% bodyfat and I haven't once gone under 2000 calories. Other than women, I know zero bodybuilders who can sustain anywhere near 1200 a day. Hell, Neggy Shelton's death was just exposed in the Washington Post from extreme dieting and she was doing about 900 calories a day, plus 2.5 hours of steady state cardio, and she was a 124 lb woman.

Those Minnesota starvation study guys you're referencing had to use an extreme deficit to get down to concentration camp weights like that over the course of a year. It doesn't say in there, but that article with Michael Rea was written in 2006, and finding other stuff on him, he seemed to have been doing calorie restriction since at least 1999. A small calorie deficit can add up when you keep at it for a very long time. Even if his TDEE was 2200 or so, that would drop 30 pounds or so in a year eating 1900.

For whatever it's worth, I've been that size, and it was not on purpose. I grew very quickly in middle school and was extremely active. By 8th grade, I was 6'2" 120 lbs and it took many years before I got much bigger than that, and I used to buy entire boxes of donuts, Little Debbie snacks, and family-size bags of potato chips on the way home from school and eat them in addition to the pizza and cheeseburgers they served at the school. And when I got a car and started driving all my friends home, we'd usually go by McDonald's every day, and in addition to just the actual food, I'd get a McFlurry, pretty much every single day.

But unlike everyone else who seems to be wondering how that was possible and what happened when they were skinny in youth, it's not a mystery to me at all. I sometimes played basketball for 18 hours in a day. When I was driving my friends home, that was usually after cross-country practice, running for up to three hours after school. I walked or rode my bike everywhere. I almost never sat down. I rarely even slept. I could eat basically anything because it may as well have been the Michael Phelps Olympics diet. I was insanely active and using a ton of energy every day.

And yeah, when life normalized in my mid-20s, I too gained a bit for a short while, then I adjusted and ate less, and now I'm very lean again, but also bigger because I started lifting and learned to eat on purpose, in an intentional, measured way calibrated to actually meet my energy needs, not just ad hoc having whatever I crave at any given minute and not thinking about it. I understand why people don't want to do this. Even though I'm not restricting like him, at least not permanently, my diet habits are basically like Michael Rea's. I weigh everything, prepare all my own food, and eat pretty much exactly the same thing every day. It probably sounds like a slog and people want to just free graze and wonder why we can't live like humans must have lived for most of the past 300,000 years, when diets and hunger levels seemed to calibrate to energy needs automatically, nobody thought about it, yet almost nobody was fat except a tiny number of super rich idle nobility. But that isn't the environment we live in any more. People are extremely sedentary and randomly selected food from anywhere is utter trash loaded with extra calories in every possible form for no good reason. Unless you have the activity level of a middle schooler from the 90s or an Olympian, you need to actually try.

Skinny people almost always eat less even though they tell you otherwise. In closely observing most, they eat less

Show me their Cronometer.com food/calorie diary and we'll see if the proposition even holds. Until then I'm not even willing to grant it's a thing.

In every case I guarantee they eat a normal amount of calories but feel like they eat a lot because they eat slightly more calories than normal in a single meal.

Like me eating two entrees at dinner at 16 and wowing everyone even though I skipped breakfast before school to play Runescape and had a tiny school lunch.

One time I tried to gain weight just to check if I was able to, as I have been unable to gain any significant weight in a variety of situation (sport, not sport; young, not that young, better/worse diet). I ate a calorie surplus diet (I don't remember the exact numbers, it was a few years ago), which meant eating more than usual but not too much either. This was measuring calories, weighting everything, all the drill; meanwhile I wasn't doing exercise other than walking/biking to places. Again, I don't recall the numbers but I gained maybe 10% of what I was supposed to gain. I've also seen how eating the exact same as other people (sometimes more) results in the other person gaining weight and me losing it, despite the differences in exercise being fairly irrelevant.

> I gained maybe 10% of what I was supposed to gain

Multiply the lb/week you were supposed to gain by 450. Your TDEE calculation was incorrect by that amount.

Those skinny people most likely have a very inefficient metabolism or at the very least a very adaptable one.

Their mitochondria use UCP1 [1][2] to generate more heat when producing ATP, thus wasting energy that would otherwise be converted to fat.

[1] https://en.m.wikipedia.org/wiki/Uncoupling_protein

[2] https://en.m.wikipedia.org/wiki/Thermogenin

so built-in DNP

I'm not saying metabolism doesn't vary among individuals, I'm saying for a given individual, their overall metabolism could decrease as they age due to having less muscle mass even if their rate per kg muscle didn't change.

What you say is true, but the main point of the paper is that they have measured a decrease of the metabolism after around 62 years even after correcting for the body composition, so the less muscle mass explains only a part of the decrease of the metabolism for older people.

The rest is likely to be due to slower rates of protein synthesis for the renewal of various body parts.

Yeah I agree muscle is a big factor, given you use it too

Casual factor. Higher base metabolic rate means less energy available to build body mass.

Fidgeting.

Then why can't someone just make an exercise program that replicates this fidgeting. How is fidgeting more potent than 10,000+ steps/day , which a lot of people do but still stay fat.

Fidgeting can make a big difference, at least it’s appeared that way in a couple sources I’ve seen referenced here in the past - failing to have those handy I found this: https://pubmed.ncbi.nlm.nih.gov/15681386/

No idea how accurate it is, but an extra 350 calories burned is a pretty big improvement over _not_ having those burned.

I doubt fidgeting alone is sufficient to keep most people skinny. There’s a lot that impacts our weight. But if somebody’s automatically burning calories because they have a hard time stopping fidgeting, that might ease the load a bit so they could eat a bit more or walk a little less than would be the case without it.

EDIT: it feels worth mentioning that fidgeting can be an all day activity for some people, 8+ hours. Walking 10k steps takes maybe 1.5 hours, more or less depending on the persons speed. It wouldn’t be as much of a workout replacement as a whole lifestyle change.

You may as well ask if John Carmack is so productive because he's really motivated, why can't someone "just" make a productivity program that replicates this motivation, and then we can all be that productive. How is 'motivation' more potent than 8hrs/day which a lot of people do and still aren't as productive.

it's not at all the same thing. fidgeting is a movement. so is exercise. productivity is something more vague.

What makes you say fidgeting is /a/ movement? Fidgeting is likely a combination of many positive and negative things; I can imagine: more anxious people are subconsciously wanting an escape from a situation and fidgeting more, more energised and impatient people are itching to hurry things up, more musically or rhythmically interested people are grooving with internal beats and earworms, uncomfortable people are pushed to move by their chair/clothes/posture/tools, it could be a form of stimming behaviour such as enjoying the feeling of the movement of clothes against skin or the finger movements taking some concentration and helping focus.

And on the negative side, non-fidgety people might be more depressed or anxious mentally, more physically drained or fatigued or lethargic physically, may have had upbringings where movement drew negative attention from adults telling them to sit still, may have social upbringings where fidgeting was seen as 'acting out', may have been part a band or group where being still was trained into them, may find their own movements distracting or annoying...

The problem is fidgetting seems to be a feedback mechanism.

Often those who fidget a lot will fidget less on days where they have used significant energy intentionally. Or will fidget less if they are restricting calories.

It would be hard to purposefully fidget a significant amount, but I suppose it could be trained with the right monitoring and stimulus. It would probably be better to train some other behavior though.

People walk 10k steps a day and stay fat because they eat too much.

The question is about base metabolic rate, not energy expenditure from exercise.

Fidgeting is a non conscious act performed throughout the day, it is not exercise. Exercise can actually reduce fidgeting and this shows up in athletes lower BMR that needs to be taken into account for meal programmes.

It is easy to eat more calories than are used in taking 10.000 steps.

Well, now I have an excuse for when people asks me to stand still. "Sorry, I cannot, I'm burning calories".

How do you know those skinny people actually have high metabolism? Have they quantified it with a resting metabolic rate test?

I have two friends like that, both were diagnosed with thyroid issues

So to answer you question, hormones

Likely genetic, such as beta adrenergic receptors.

This is exactly the kind of clear headed reasoning from prior knowledge I love coming to Hacker News to see. You're right. Thank you for the extra bit of gym motivation.

No mention of how a persons lifestyle changes over that period though.

Surely there is a correlation to the causation?

The head-bone is connected to the neck-bone etc...

You cannot study figures in isolation and expect them to yield some meaningful results while ignoring the influence of other figures upon those results.

- Kids move around a lot, and they're still growing/developing

- Teenagers move more constructively i.e. sports, and they're still growing/developing

- Adults move a bit less, and have almost stopped growing/developing

- Older adults try do keep moving, but with other life responsibilities it gets hard to put the same time in

- Older adults become less and less bothered about moving

- Even older adults have acquired illness and injuries and can't move as much

Seems quite simple and obvious no? - Maybe...

Those that don't fit the mould have some other reason that makes then more of an outlier to the norm.

If life today didn't offer as much assistance as the past, we would all be a lot more healthy - not to mention more active, you know walking and manual work etc...

Not to forget that the abundance of food (good and bad) will have a bearing on the results. Maybe the older people that can't afford as much food are the outliers - and better benchmark.

Unless you are suffering from malnutrition, or you are overeating the wrong sort of food (good and bad) then your metabolism, unless affected by biological factors should be pretty stable.

Isn't this what being in homeostasis means?

Doesn't the body adapt to effects of S.A.I.D. - Specific Adaptations to Imposed Demands.

If inactivity was the explanation, it logically follows it would be possible to undo obesity by simply having people move more, but the evidence suggests exercise does not help compared to diet.

https://cdn.vox-cdn.com/thumbor/U1RxtW9oglcck-2g2X_SrKzIA44=...

With no further context that graph is simply showing that exercise increases/maintains lean mass which will slow down absolute weight loss during a calorie deficit.

There's no exercise-only group on your graphic. So even though it's some random data without any context, it still can't say what you conclude it said.

Did anyone happen to read any of the responses to the article at https://www.science.org/

It seems that others don't fully support their findings either.

https://www.science.org/doi/10.1126/science.abe5017#eletters...

The only criticism I see is some nitpicking saying that the claim “was based on statistical means, ignoring the known intense drops in the energy expenditure that some individuals show during their life. For example, a clear decrease in metabolic rate is observed in humans that consume calorie-restricted diets (Fothergill et al. 2016), an adaptation named ‘metabolic slowing’ (Johannsen et al. 2012). Therefore, the statement is innacurate and possibly wrong.”

These critics don’t seem to disagree with the core claim about average metabolism across the lifespan.

* Extreme events reveal an alimentary limit on sustained maximal human energy expenditure.

"We compiled measurements of total energy expenditure (TEE) and basal metabolic rate (BMR) from human endurance events and added new data from adults running ~250 km/week for 20 weeks in a transcontinental race. For events lasting 0.5 to 250+ days, SusMS decreases curvilinearly with event duration, plateauing below 3× BMR. This relationship differs from that of shorter events (e.g., marathons). Incorporating data from overfeeding studies, we find evidence for an alimentary energy supply limit in humans of ~2.5× BMR; greater expenditure requires drawing down the body’s energy stores. Transcontinental race data suggest that humans can partially reduce TEE during long events to extend endurance."

https://www.science.org/doi/full/10.1126/sciadv.aaw0341

Another sobering result for the fitness industry, that convinces 30 year old men to be on TRT.

TRT is great for people who have true hypogonadism that can’t be fixed by other means. I had a friend growing up whose testosterone was under 100ng/dL no matter what he tried with his doctor. Finally got TRT and felt normal again.

However, after the honeymoon period the experience made him realize that not everything is explained and fixed by testosterone. He still had some mental health issues, he still had to work for gains at the gym, wasn’t suddenly full of boundless motivation. All this despite being put toward the upper end of the range for a long time.

This seems to be playing out with a lot of young people going to TRT clinics: The TRT clinics are prescription writing factories that will find an excuse to give almost anyone TRT. They make claims that the normal ranges are wrong and the only correct result is to be at the top of, or above, the reference range. They start people on insane beginning doses like 250mg/week because it gives them a rush to feel like it’s “working”, especially before their natural production shuts down.

The clinics also try to lock people into getting their prescriptions from the clinic in a subscription model. They basically get people hooked, literally dependent on testosterone because their endogenous production has shut down, and then require them to order the testosterone through their pharmacy to continue receiving the prescriptions. If they go to a family doctor, the family doctor will probably decline to continue writing such high dose prescriptions because high doses generate significant side effects, so the person returns to the TRT clinic.

It’s really bad out there. I think we’re headed for tighter regulation of these clinics soon, or at least I hope so. Every time I listen to the radio I get several ads for different clinics every hour promising men they will lose weight, be better in bed, have more energy, conquer the world.

I had low testosterone due to a brain injury, and going on TRT was absolutely life changing. I do wonder if it could be largely beneficial for older men in the same way hormone replacement therapy for post menopausal women is.

That said, permanently messing with your hormones as a younger person for no good reason is insane and I would try to talk anyone I knew out of it.

Fun fact: I had an endocrinologist at the University of Minnesota medical clinic tell me that going on TRT wouldn’t affect my fertility. Cue IVF 8 years later…

I'm only 30 and no plans on going on TRT soon, but I definitely plan to if my levels start to get below the normal range for a substantial period of time just based on all the positive effects being in the normal range brings.

I am highly into fitness myself, but I know plenty of either friends or people I've met who are already getting TRT mostly because they want it to help them, but many of them have so many other issues that its just masking when it comes to things like diet, training, consistency, etc.

Additionally in the fitness world many go on TRT even when they already have normal test levels partly because they don't see it quite as "cheating" as other performance enhancing drugs are seen.

Did you have hypogonadotropic hypogonadism from the brain injury? If you did the endocrinologist is right about the TRT. Without TRT you would have been infertile because you lacked GNRH/FSH/LH from disruption of your hypothalamic pituitary axis due to injury. Your Leydig cells would not be able to produce local testosterone in your testes for your Sartoli cells to utilize in spermatogenesis.

With TRT you would have systemic androgen but not high enough in your testes locally for spermatogenesis. So with or without TRT you would be infertile (if you have hypogonadotropic hypogonadism)

It was never ruled one way or the other and the brain injury is just a theory based on the start of my symptoms (along with losing height after), but to quote him "if TRT worked to reduce sperm counts enough we'd be using it as birth control." He wasn't talking specifically about me.

From what I remember my FSH and LH were normal. I don't recall GNRH being tested.

Usually with pituitary axis injuries the other hormones are affected as well and not just FSH/LH.

The FSH and LH being normal with low testosterone means there’s some kind of dysfunction. There’s an inverse relationship and if T is low LH should be higher to induce synthesis.

Sort of like in women’s menopause - when the ovaries run out of oocytes the ability to produce estrogen is gone and FSH/LH increase.

Anyways, obesity could be another issue. Adipose cells produce estrin and estrin has promiscuity with the estrogen receptor which reduces testosterone production. Another is elevated prolactin which has multiple causes and can reduce T production.

Anyways, my caffeine ranting is at an end. Good luck

Convincing men at basically peak testosterone production to permanently impair their natural ability to produce it. It's awful. Not to mention the side effects of taking exogenous hormones e.g. damage to your liver...

I see a study suggesting that, in hypogonadal men (important), TTh or TRT seems to improve their liver.

This seems to be contradicting your claim: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8451678/

Did you read the study? Or even the first line of the abstract? “Hypogonadal men with hepatic steatosis” is literally in the first sentence.

It’s a study on men with low testosterone and fatty liver disease. They already have damaged livers.

If the presence of testosterone can improve the function of damaged liver, there's no reason to think that a healthy liver would get damaged by it. I can't even think of any mechanism that would be involved.

dosis sola facit venenum? Sorry I can not say anything smarter because I can not compare the doses, but maybe someone else will compare.

Peak? We're talking about 30 year olds.

For some it's not really convincing. They look at it like doctor perscribed steroids.

Never mess with the endocrine system! the real killer for mens T levels, ie the perception of low T, is sitting around all day. I'm convinced that most people, men and women, feel terrible because they simply don't do nearly enough physical activity day to day. 20 hours of screens a day is not normal.

Super useful outcome, especially given I find that people think that after reaching even young ages 24, 25 even begin thinking that metabolism has some extreme drop off right after reaching young adulthood

It’s an inevitable outcome of a culture so focused on age. I watch twitch streamers in their 20’s talking about how they’re old already. Narcissism isn’t just a social phenomenon spread online, I think it actively contributes to many public health concerns we’re seeing today.

I agree with your observation, but at the same time, I do think that what a lot of these people might be expressing is their observation of the disconnect between their socially implanted expectations (you're an adult when your 18/21! you are now -mature-), and their experience reality. Which is that for many (most?) people who go through the typical North American education pipeline through university/college (and I'm only making this limitation because that's my experience, and the experience of most of my friends), that looking back, they were definitely not "mature" at 18/21. They probably weren't even mature when they graduated undergrad or started their first full time job out of school.

Everyone has a different point, but they typically recognize somewhere in their 20s that 'oh wow, we keep changing and maturing'. And the first, most basic way to express this observation is with a pretty crude 'oh wow I'm old'. I think eventually, most people can move beyond that first reflexive observation.

I some times make the following observation:

When I was 15, I thought I had grown up quite a lot and looked back on my 10-year old self as someone who was just getting started.

When I was 20, I thought I had grown up quite a lot and looked back on my 15-year old self as someone who was just getting started.

When I was 25, I thought I had grown up quite a lot and looked back on my 20-year old self as someone who was just getting started.

When I was 30, I thought I had grown up quite a lot and looked back on my 25-year old self as someone who was just getting started.

Now that I'm 37, I think I have finally grown up and my 30-year old self was just getting started. But I recognize that my 42-year old self will probably look back on me and still see the same pattern.

6 years ago I was an idiot.

6 months ago I was an idiot.

Last week I was an idiot.

...

Glad I'm smarter now.

So the results show that on average, metabolism is stable from 20 years onward. That means that there actually is a drop from 18 to 25 (it's there for men at least when you look at Fig 2). Now think about where most people will be anchoring their perception of "adult" from (it's going to be some value in that range). That means that there will absolutely be plenty of people who experience a real decline in metabolism in the years following their "personal adult threshold".

Now, that's a pretty small drop, so definitely the other life transition (probably starting an office job, living alone) will probably play an even larger part to any weight related changes. But even given a hypothetical case where someone kept the exact same activity level, the amount of metabolism decline over that period is probably small enough to delay the onset of any noticeable body composition change (like order of 10 pounds) for a few years, adding to the mid to late 20s experience.

Such rumors are created and spread by people who want an excuse rather than a solution. This wont help them since they want to cling to their excuses, but it can help others ignore those rumors.

I found the misconception useful because it prompted me to invest time in improving my diet in my 20s, before it was too late. Even if my metabolism has stayed the same since then, the no-vegetables-or-fruits approach would have caught up with me at the same time "low metabolism" would.

Anecdata: I ate 3500-4000 calories a day of mostly junk in high school and college. I lifted weights some. I (barely) “had a six-pack”. No sports, only incidental cardio.

Around age 21 or so, I decided to try to drop a couple pounds and make it a really cut six-pack. I ate a strict 1400 calorie diet (packaged food to make it easy, no cheating at all) for about three months. I started running a couple times a week. I’d reckoned this would only take a month or so. Found the calorie deficit pretty easy, actually. Three months in, the scale showed one pound of loss.

Discouraged, I returned to my old eating habits.

I immediately gained about 15lb. Had to drop soda completely to stabilize it (i didn’t drink much alcohol then). Slowly got worse through my 20s. By 30, not turning into a blimp required a careful diet. No more 4k+ calories of pizza, soda, and potato chips without (visible) consequence.

My metabolism 100% for-sure changed in my 20s, a ton, not gradually. But I may have killed it, and perhaps I would have been able to keep doing what I was doing another couple decades otherwise (I would bet zero dollars on it, but hey, I guess the science disagrees, I just find it literally incredible)

I don't buy your anecdote.

Those are the figures people always estimate. Always the same story: 4000 calories when they were skinny, and now they can't lose weight on 1500 calories when their maintenance intake is 2600.

Then you make them log their food for a week and they are eating 3000 calories when they swore they ate no more than 2000. In my 20s I worked at a personal trainer in a gym that made people log their food and 100% of people said the same thing you just did.

If you couldn't lose weight on 1400 calories then where exactly was the energy coming from? Cue the "starvation mode" meme where people claim their body becomes so efficient that it only needs 1400 calories to maintain their 270lb body.

> 4000 calories when they were skinny, and now they can't lose weight on 1500 calories when their maintenance intake is 2600.

4000 is a conservative estimate. Four pop tarts, an entire large pizza (all you can eat buffets FTW), two liters of soda, and an entire large bag of chips was, like… a totally normal day for me. There’s probably also be some cookies or hostess donuts in there, too.

> If you couldn't lose weight on 1400 calories then where exactly was the energy coming from?

No clue, but I didn’t cheat once and ate fixed meals of pre-measured calories every day. So.

Teens are growing until early 20s that’s why they can and do eat so much. When you stop growing you enter into your adult metabolism.

I started gaining weight/fat in my mid 20s and had to adjust my eating habits from what was normal in the preceding 8-10 years

Sure, hgh+T is a hell of a combo, but TFA claims a gradual change from teen metabolism in one’s 20s. I experienced a switch-flip that cut north of a thousand calories of apparent metabolism in a matter of months.

but the article says it's gradual. gaining 20+ lbs in a year not gradual.

same here but at a later age

this seems to agree with a lot of people's personal accounts. A switch is flipped in which the body for whatever reasons starts hording energy. maybe it is stress from family life or work related... who knows...The weight comes on so fast... it's nuts how much weight some people gain starting at 25 or so. Guys who were 130-180 lbs lean in college now 240+ lbs all a sudden at 30+.

According to the paper this is "Fat-free mass-adjusted expenditure", and testosterone DOES start to slowly decline after around age 25. The trouble people have with starting to gain weight easier as they enter their 30s and 40s is caused by this since they'll lose muscle mass as such hormones decline, which causes fat gain assuming similar food intake and activity levels, this effect is not included by adjusting for fat-free mass.

I also think 30-40 is more likely caused by life just being more complicated! Juggling kids is basically a full time job, and many families are two income families. Hard to hit the gym when your child, who cannot be left alone, increases your effective work hours to 80-90/week minimum no vacation no breaks.

Anecdotally: I havent changed diet one bit, actually I eat way healthier than when I was younger.

And still weigh much more than when younger.

I think thats basically true for most people, hence the belief that metabolism slows with age.

Proving that its not metabolism would imply that our weight gain in later life is a combination of other factors. I would bet good money on the increase in sedentary leisure activities, the reliance on motorised vehicles and a lack of energy to be active.

I would bet on those long before anything as nebulous as diet or intake volume.

Have kids and compare yourself against them. It truly sobering to see how much relentless energy hey have, in body and mind (and when they hit the wall with burning out all energy, they hit hard). All the movement is just burning through all energy. I feel myself very active, but next to my 3 year old son I feel glacial and lazy.

We can reverse that, like we can revere many ways we slowly decline, just need a right mindset. Spend a really active vacation or start a new sport and lack of energy of yesterday will be gone, to certain extent. One can always do some dramatic change in lifestyle to see a dramatic change in body, weight, strength, stamina etc.

I see as people get older their mental model of how they behave and think often mimics somebody much older than their actual age, acting as if they are completely powerless to greater evil forces of muscle atrophy and weight gain. It simply ain't true but going against it is certainly harder than just complain.

I can think of two major, extra lifestyle factors that increase calories in adulthood that we overlook in favor of more appealing explanations like "metabolism tho":

1. We eat out more as adults. Our skinny kid/teen selves didn't even have the money/vehicle/norm to eat out much less do it daily like we can as adults. This also includes eating out during our lunch break. Every time we eat out that's an easy 1000+ calories.

2. When you live with a partner, every time they ask "wanna eat something?" and you say "yes", that's a moment you wouldn't have eaten had you been a bachelor. We'll even say yes when we aren't hungry.

It's funny how much we want to believe in factors out of our control.

Alcohol consumption is probably in there as well.

yep, so many people go from 10k steps a day in college to 5k in an entry level position to 1k in a desk role. for a 200lb 6 ft tall male, thats 3000 kcal burned a day to 2600, to 2300. 700kcal a day being a weight change total of around 1.5 lb a week when you consider days off.

Multiply that by 15-20 years and you’re looking at a solid extra 200lbs you have. Naturally every 40 or so makes you look in the mirror, make some minor changes that last a year or maybe a bit more and it’s back to getting out from under the gelatin we’re packing onto ourselves.

In order to really, truly, get a handle on your weight - you need to increase muscle mass, operate at a slight caloric deficit, eliminate excess calories, and forgive yourself. The easiest way to distract you from excess calories is by doing something that keeps you busy (and hopefully works those muscles). Bikes rides, hikes, climbing gym, treadmills, skating, skiing, walking at a faster than moderate pace, running, weightlifting, tree cutting, brick laying.

People often get demotivated when they call it “working out”. Instead, just call it “working”.

Then why do so many people go to the gym, do 10k steps/day, intervals, etc. yet do not lose weight? Americans are arguably more active and health conscious than ever before as evidenced by the huge popularity of fitness content on YouTube, record number of gym memberships and attendance, the huge popularity of fitness apps, awareness of GMOs, food tracking apps, etc. yet fatter than ever too.

Because they don’t control their portions or eating habits. Take a look at the UK TV show “Secret Eaters”* which sets up secret cameras in and has investigators follow a different household every episode to estimate everything they eat down to the tablespoon of sauce. It’s an eye opening look into psychology. Lots of people think they’re eating 2K kcal or less but are in reality consuming 3-5K per day.

* full episodes on Youtube

This is the biggest culprit. Snacks, portion control, mislabeled calories. For example, Pringles says it’s 160 calories per serving. Serving size 4 chips. Most people eat 40.

food tracking apps

Food tracking is completely useless unless you also have a food scale, which, for whatever reason, is not terribly common in American kitchens. At least I never had one growing up and my Mother fancied herself a serious baker. Volume measurements are terrible if you are trying to track caloric consumption.

And I have not used a food tracking app but they appear to depend on honest inputs. I can just imagine someone telling their friends, "I don't know why I'm gaining weight $FOOD_APP says I'm only eating 1400 calories a day", somehow forgetting to put the 3 glasses of wine they are consuming into the app.

So totally IME but the best way to lose or maintain a healthy weight (whatever that means to you - the world really doesn't care) is to have an honest, internal drive to get it done. No one, no app, is going to do it for you. Do the cookies in the break room look good? They sure do, but I like my body far more than those cookies.

Americans also eat more portions of food. Super sized. We also don’t eat the right kinds of foods. Opting for quick serve processed foods vs natural ones.

No amount of leg work will reverse putting garbage in your body.

I’m a 6’0 man who went up to 220lbs when I started working a desk job that provided sodas on demand. When I left there and went somewhere I needed to walk to eat lunch to I lost 30lbs and now hover around 190lbs.

When I learned how to swim last year that dropped to 175 ish and would’ve probably kept dropping if I spent more than 3 months going to the pool for an hour a day twice a week.

Swimming is where it's at! Sounds like a little went a long way.

If inactivity were the explanation, it would be possible to fix obesity by having people be more active, yet this this does not work :

https://cdn.vox-cdn.com/thumbor/U1RxtW9oglcck-2g2X_SrKzIA44=...

exercise not help at all. the body compensates in many ways

400 calories burned from a run does not magically offset a donut. The conversion rate may be flat or even negative.

source: https://www.vox.com/2016/4/28/11518804/weight-loss-exercise-...

Anecdotally, to me it seems like my metabolism hasn't changed. I was overweight when I was younger because I overate. Now I don't, and my weight is normal, on the low end for my height. But nothing about the quantities turning into pounds changed, from my p.o.v. (mid 40s now).

Actually the main thing that changed for me is I started compressing all my eating into 1-2 meals per day. That way I could track it. Before I couldn't tell you if "I haven't changed my diet" because it was a continuum of eating from morning till night. I have no idea what changed over time, couldn't even tell you for one week. Once I "bounded" it I was able to bring my weight down quickly.

Btw, sorry if this sounds snarky, it seemed like flagging this as anecdotal was the right way to start so I copied it.

That is likely down to the type of "food" that you are eating. Or you are eating more than is necessary.

A diet that contains a high nutritional content will prevent you from over-eating due to satiety signals (unless you have a hormone issue) rather than eating to the point of feeling "stuffed" - if someone is eating to the point of feeling "stuffed" then it would suggest that they are not eating food with a high nutritional content, or that they have some disorder that is interfering with their normal eating process.

If you look to the animal kingdom, the lion kills the zebra, feeds then walks away, the next in line feeds, then walks away, etc, etc... no animal eats until they are "stuffed" - if they did then they would become another animals prey because they are too "stuffed" to move!

No wonder some countries consider it rude to clear your plate of food. (too bad the Brits do this the other way around!) lol

if this were true it would be possible to create a diet full of foods with such satiety signals and the obesity crisis could be fixed. way easier said than done. 7-grain bread is very nutritious yet a loaf is easily 1000+ calories. Easy to overeat on it given it's just mostly air.

Carbohydrates, including starch, are not effective in creating long-tern satiety.

The satiety after a few hours since a meal is mainly determined by the amount of proteins and of fat contained in it, not by the amount of calories.

For instance, after a meal including 50 g of proteins and 50 g of fat, most people would not be hungry for at least a half of day, or even for an entire day.

If you remove from your 1000 kcal loaf of bread 500 kcal of starch, which can be done by washing the dough before baking the bread, and you eat the result (i.e. a bread greatly enriched in proteins) together with 50 mL (46 g) of olive oil, you will eat less calories, but you will be satiated for many more hours.

7-grain / multigrain bread is still a highly refined thus a highly palatable product despite the healthwashing of the name compared to whole grains.

A better example would be something like sprouted whole grain bread, like Ezequiel brand, which is hard to eat plain. If everyone replaced their wonderbread with whole grains I would absolutely expect better body weight outcomes.

I mean from a survival perspective bread is incredible: the amount of calories it fits in versus how easy it is to eat, the increase in durability. It's not surprising it became a staple as soon as agrarian civilization happened...it's just we're also not subsistence farmhands anymore working in fields all day.

Without a meticulous food diary for comparison, you can't substantiate that you are eating the same or fewer calories. And if you can't do that, then there's no mystery here.

If you are eating 3000 calories of healthy food and you used to eat 2400 calories of junk food, why would you weigh less now?

Are you eating with the same consistency as when you were young? Are you walking the same amount as you used to? Are you partying with the same frequency? Etc.

Eating too much for sure. When younger average person spend more time outside, traveling more etc.

There's a theory that you're gut is optimizing over your life. So you were young, and you could eat garbage by the truck load and not see a pound. You're now eating better and exercising portion control, but your body has learned how to extract everything it can from food.

USA based. I was born in 1968 rebelled against my organic gardening and bread baking mom every chance I got. I weighed around 135 pounds in college and currently weigh 143. I have been as heavy as 147ish that I noticed.

There is probably some larger environmental factor that causing the majority of people to gain weight. Whatever it is started in the 1970s in the US, and has since spread to most of the rest of the world. Possibly plasticizers, or some other chemical. Even children are much heavier now.

I ain't buying it. There is a replication crisis in the sciences, and it would not surprise me if this is wrong too, or at least that the results do not mean what they are purported to mean. I have read many personal accounts here and elsewhere of men who were able to eat a lot in their late teens, 20s, and early 30s, and then suddenly by their 30s gain a lot of weight despite not changing their lifestyle or diet much.

Inactivity alone does not explain it. Consider for example Bill Gate...according to his resume, in which he lists his precise height and weight, in his 20s he weighed just 125 pounds. It's evident he has put on a lot of weight, all in his mid-section, well before he turned 60. His job literally entailed sitting at a computer all day coding. If anything, given his philanthropy efforts and retirement, he is more active now than he was in his 20s when working full-time at Microsoft. Is he eating more? I doubt it.

For so many people, celebrities for example, a switch is flipped in which there is sudden weight gain after the age of 30 or so, like John Travolta, Stevie Wonder and others. Because celebrities are photographed, you can see the weight progression and the abrupt jump in weight. Even with money for personal chefs and trainers, not gaining weight is hard.

I can personally attest that if I ate the same quantity of food now as I did at 20 I would gain weight, and no I'm not 60. And I am just as active , maybe more so. So yeah not buying this study.

> Is he eating more? I doubt it.

So, four paragraphs all based on this assumption.

Why couldn't it be the case that a 20yo obsessive computer nerd eats less than a lavish billionaire?

What's the age at which anti-aging interventions are most impactful?

I assume they don't help much when you're young, because you're already healthy as a youth.

Presumably waiting until you're on your deathbed to start high-intensity intervals is not the best idea either.

Supposing a person had a limited budget of "anti-aging firepower" in the form of pills, exercise, etc. -- what age would be most impactful to apply it?

That is way too complex a question to answer here. If you really want to dig into it including exercise, nutrition, sleep, and medications then the new book "Outlive: The Science & Art of Longevity" by Dr. Peter Attia is a pretty good summary of what we currently know.

https://peterattiamd.com/outlive/

I wouldn't think of this from a limited budget perspective. Much of what you can do is cheap or free. It doesn't cost anything to go to sleep earlier.

This doesn't seem to line up anecdotally;

The first outlier I see is female health and PCOS, starting in mid 20s for women.

The next outlier I see is insulin resistance and pre and diabetes based metabolism decline.

From a hormone perspective, nose, ear, chin (femalr), and head hair seem to be going under significant change.

Mid 20s with when your lifestyle shift just starts to catch up to you.

You go from a more active young person that eats just enough to get back to hanging with friends to binge drinking in an instant. Then you go from that to a much lazier, snackier lifestyle of 9-5.

Yeah, people on the whole do get fatter in their 30s, but that’s very easily linkable to lifestyle.

This is caused from eating too much, not a decline in “metabolism”

So, the combination of the research and my anecdotes - and your response seems to be

That by our early 20s our metabolism has already slowed (sugary food, alcohol, precipitous drop in activity)

No, our metabolism isn't "slow" (for 99% of people). People just start eating much more and moving much less.

Insulin resistance and PCOS absolutely have effects on metabolism. It’s very well studied.

how many outliers or exceptions do you need before you can throw out the theory

This is interesting for me to see. For the longest while I was wondering why through my 40s and later I didn't seem to be hit with middle-aged weight gain, all while living my sedentary life in the computer chair. I wouldn't classify myself as average though, I've always had low heart rate/low blood pressure and low blood sugar. Swimming in salt-water is fun because I can float without much effort.

I did notice a decline in metabolism/muscle mass in the past several years, so I took to walking rather than driving in the city/neighbourhood and eating more and regularly which seems to have brought my levels back up somewhat. Now I look like someone who only goes to the gym on leg days.

This was completely expected, at the macro level this is easily observed by measuring the outputs of metabolism and bodily function, mainly heat and physical activity. All humans have a baseline bodily temperature, meaning that the inner metabolism also is the same across all humans.

Sweating at different rates, surface blood vessel dilation including in your lungs, all change the flux. Having longer hair or wearing warmer clothing can too and can be balanced by those other things. Activity also gets balanced by those things. Eating cold food and drink vs warm etc.

That we maintain a baseline temperature doesn't tell you that metabolism alone is all that regulates it, there are other factors.

Your body can change the temperature gradient near its surface to retain or expel heat without a change in metabolism.

metabolism varies greatly controlling for height, activity level, and weight . sometimes as much as 600 kcal /day

"Humans are spherical cows"

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