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Comment by peterwwillis | Hacker News Reader

Intermittent fasting seems like it'd wreck your body if you do moderate to intense exercise. So I just fasted, and now I want to do intense cardio.... but I might run out of glycogen or blood sugar. Or I may do a set of weight lifting, but not if I can't eat protein after. So if I do intermittent fasting, I have to come up with a complex schedule to follow in order to get any performance gains.

The whole point of a diet is to be healthy. You don't need intermittent fasting to be healthy. It seems to just introduce complication for a menial improvement in a few measures of health. I'm sure they work, if you can actually stick to them, but there's a lot simpler diets that will also work.

Exercise three times a week. Eat lots of plants. Keep your fat, protein, and simple carb levels within reasonable limits for your age, height and sex. That's not super complicated to follow, and it can fit into basically any schedule.

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Nah, that's complete BS. Fasting doesn't impair you to the degree you're implying. It takes a good 24 hours to run out of liver glycogen, and even then it's not like you keel over, you just have maybe 85% of non-glycogen-depleted performance. Just have a meal at some point the day before your workout, and you'll be good to go. Blood sugar is also a non-issue when fasting. It is in fact more stable in a fasted state due to very steady insulin levels. Humans are not fragile creatures that need to eat every X hours to do physical tasks.

I do heavy weight lifting in the early morning and fast every day until 2 PM. You don't need to eat protein right after you lift weights, later in the day is perfectly fine. For you optimal gains, maybe, but for gains, no. But I'm not a world-class athlete, I'm a 31 year old with an office job. Intermittent fasting is very popular in the weight lifting world, and it works very well. In my experience, lifting in a fasted state impacts my performance 0%.

This matches my personal experience. I found the gains acquired while IFing - exercise at around 8pm after work and fasting afterwards until noon the next day - to be very consistent and lean.

Same I do time boxed intermittent fasting, usually exercise in the morning, and eat a single large meal between 2-7PM. I primarily do cardio (distance running), and didn't notice any performance hit.

Early on when I was still experimenting with the diet, I did drop down to around 160-165lbs, and my running performance took a drastic hit. I remember struggling to complete a three mile run one day, when 6-10 was typical for me at the time. I felt normal up until around one and a half miles in, then I hit a wall, which made me turn back early. It was a really odd sensation, the will was there, but I was weak, almost like I had run out of gas. I'd tell my legs to move, and they'd barely follow through. This wasn't soreness, or fatigue, but weakness, subjectively a very peculiar sensation, and not at all subtle.

Being weak like that did freak me out a little bit. I simply added more calories (ate more), while maintaining meal timing, and my distance was back to normal in a week or two though (actually slightly better than my pre-diet "normal"). This brought my weight up to a steady 170-175lbs, which I've been at for about two years.

It's really important with this style of diet to get adequate nutrition. If you're eating less, or timing your meals, you really need to maintain a high-quality diet. You're likely eating less than most other people (or what you're used to), so the nutrients and calories you do take in are that much more important. Eat a lot of fresh vegetables, moderate carbs, and high-quality protein. Extra fiber is also really important, because the extra volume helps create a sensation of fullness, making the diet easier to stick to. You'll also want to drink extra plain water, to accompany the fiber, so your body chemistry doesn't get out of whack. Don't eat any refined sugar at all, it's a powerful appetite stimulant, and will make the meal timing much much harder to stick to.

> lifting in a fasted state impacts my performance 0%

Based on my own experiences, I'd actually expect performance to improve since the body isn't using resources for digestion. I'm not a weight lifter, but I know bicycling is significantly harder shortly after eating and my other current sport, freediving, is much, much easier after fasting (my static hold time is close to 2 minutes longer when I haven't eaten in the past ~12 hours).

One interesting observation I've had from freediving is that some of the signals we get from our bodies are far less urgent than we tend to experience them. The main one, in that sport, is the urge to breathe and it's actually not an indication that the body needs oxygen. It is, instead, an indication that CO2 is building up and you can expell it by breathing. Freedivers learn to experience that sensation and push past it.

I'd imagine hunger is very similar. People accustomed to eating whenever they're hungry will panic an experience "low blood sugar" when they don't immediately respond. But we know that humans can go weeks without eating before we die. Pushing past our accustomed non-resistence to hunger will likely be uncomfortable, at first, and then become normal with practice.

"I'd imagine hunger is very similar. People accustomed to eating whenever they're hungry will panic an experience "low blood sugar" when they don't immediately respond. But we know that humans can go weeks without eating before we die. Pushing past our accustomed non-resistence to hunger will likely be uncomfortable, at first, and then become normal with practice.

Exactly. People are way too used to eating all the time.

>I'd actually expect performance to improve since the body isn't using resources for digestion

This is exactly what I've noticed as well. Even a few hours after eating my runs feel sluggish. All my PRs are from running first thing in the morning, before any food.

Intermittent fasting is probably fine as long as you only have an hour or less of exertion on that day. Do 2+ hours though and I think it's a pretty bad idea.

And in my experience even just doing an hour of exercise in a fasted state can dramatically impair my immune system as well as higher brain function.

I don't know 100% for sure, but I think this may have more to do with how many calories you're eating over time total vs how much you eat near exercising. A caloric deficit on its own will do all the things you've named regardless of feed windows, and I haven't experienced any of them while intermittent fasting. But I can't say for sure if I've ever had 2+ hours heavy exertion while doing IF.

Doesn't ketones... work roughly the same as glycogen? I'm doing keto + IF (modified, I have a noon'ish protein drink, and then a meat heavy dinner). Just wondering if you've heard that, I'm new to working out (started at 515 down to 485 in 5 weeks, lots of muscle gains too though so fat loss is probably a lot better than if I'd just dieted alone.)

Edit: I mean, I read an article once that said ketones could enhance performance in weight lifting.. my exercise is Cross Fit training at a Crossfit gym.

It's not really that hard to do intermittent fasting. You just eat dinner at 6-8 PM and then skip breakfast and eat lunch at noon.

And IMO the "risk" of bonking is hugely overblown, the worst case scenario is you're in a bike race and you have no energy. Most people are not racing bikes, so I don't see what the big deal is. You stop your workout and eat something. Most people's cardio workouts are not long and intense enough to bonk in the first place, even if they're fasted for 16 hours.

I've bonked riding bikes multiple times even when not fasting. I don't see it as a risk, you just limp home @ 20km/h. Sure it sucks :)

> Intermittent fasting seems like it'd wreck your body if you do moderate to intense exercise.

That just seems highly unlikely from an evolutionary perspective: food sources for most animal species tend to be inconsistent and require physical exertion to exploit (especially for predators).

If hungry + physical exertion = damage, you'd expect that to get weeded out of the gene pool. Human populations have certainly gone through regular famines and starvation during our history, while still needing to farm manually.

> So I just fasted, and now I want to do intense cardio.... but I might run out of glycogen or blood sugar

Isn’t that where ketosis comes in? Your body can break down fat and provide energy through ketones.

Some proponents of intermittent fasting would probably argue that simply not eating at certain times is the simplest diet of all since it doesn’t require continually evaluating at each meal what a “reasonable” level of intake is.

It takes between 2-10 days to reach ketosis and switch from using carbs for energy to using ketones. Burning ketones also brings less energy than burning carbs, which would not be ideal for cardio.

You don’t have to be in ketosis to burn fat for energy. Ever notice how cardio gets harder about 45 minutes in but then gets easy and you can go on for hours? That’s your body running out of stored carbs and switching to burning fat reserves.

There are studies on keto-adapted athletes doing cardio, from what I can tell there is no detrimental effect from a ketogenic diet after about a month of adaptation:

https://www.sciencedirect.com/science/article/pii/0026049583...

Thanks for this, I'm doing a modified fasting regime + keto + crossfit. I started at 515#, 5 weeks ago. I'm 485 now. I have a smaller stomach from surgery in 2012 but I only lost 150 pounds after surgery (650-500). I've been yo-yoing between 450/510'ish.

My daily diet is basically a 8 carb protein shake with 60g protein around noon. Then the equivalent of 2 hamburger patties and 1/4 cup cheese for dinner. My calories rarely exceed 800 though. I feel great -- more energy than ever, and I have 0 hunger, I have to force myself to eat.

I'm hoping this is maintainable and that I can keep the momentum up. My wife has a baby due in January (our 2nd), and I want to be able to do more with the family/kids and be around for them. Luckily I have no co-morbidalities, I just did a full physical -- everything is perfect # wise blood pressure, lipids, vitamins (except D deficiency). But, I'm 38, that could change. My heart could get stressed from the weight in a few years... I've been seeing a therapist for depression, and a doctor for ADHD, and now doing a good fitness regimen.

Last year I was depressed with very dark thoughts, this year I feel great and in more control.

Fasting followed by cardio is a thing. It's called "bonk training". Running out of glycogen is the whole point of it.

It supposedly helps your body make the switch from glucose and glycogen to body fat and ketones more smoothly. It might have been useful for triathletes and marathoners, if they weren't eating glycogen gel during their races now. You'd carbo-load, hit the wall at mile 20 or so, and just keep going at 80% your normal athletic capacity instead of 70%, because you trained for it. But now, you'd just be left in the dust by someone who has been sucking on a tube of glycogen gel and thus never hits the wall at all.

I suppose it would still be useful for weight loss, if exercising while bonked wasn't self-torture.

you can't go as fast

If you aren’t diabetic, you need to do hours and hours of intense cardio to Bonk (run out of glycogen).

As long as you’re not doing whole day fasts, I don’t think the burden of effort is any higher than the protocol you’ve outlined.

When beginner discipline is the subject, simple rules tend to work better. Your confidence following simple rules allows you to then tolerate more complicated regimes.

Edit to add: Personally, I don’t agree with ADF but for strength training your muscles are rebuilding for days afterward. If you’re trying to gain muscle quickly you’ve probably already decided ADF isn’t for you. But to maintain or gain slowly? I’m not sure it’s going to slow you down that much.

The rules are psuedoscience peddled by health gurus.

I'm not familiar with the term bonk, but I thought the glycogen in each major muscle ran out after about 20m? I've read many times that during cardio the body starts burning fat only after the first 20m. Then it releases a chemical to begin burning calories from fatty tissue.

Your liver also stores a significant amount of glycogen that it can release into the bloodstream. "Bonking" is a term from endurance events, for example in a marathon bonking typically takes place around 20 miles into the race when runners have been running for more than 2 hours, which fully depletes their glycogen stores. Modern runners typically refuel with carbohydrates, drinks/gels, to delay bonking, but depending on pace and time you typically can't consume enough calories to fully replenish what you have used and will bonk eventually. Then you will need to continue at a slower pace burning fat for fuel.

I’m an ex cyclist but occasionally I like a bit of nostalgia. This recalls to me one conversation with a coworker who pointed out that while exerting yourself you can only absorb around 600 calories an hour, but as we know, you can burn thousands.

You have what’s in your muscles, liver, stomach, and whatever your body can cannibalize from fat and muscle. If you go long enough (without overdoing it) you start burning muscle, which is a really good example of why recovery and pace matter so much. And why runners and cyclists have those wiry little arms.

Friday99 gave a pretty good explanation but to offer a little insight into the experience: your brain runs on glycogen too. The Bonk is what happens when your glycogen stores crash so far that your mental capacity is diminished.

Smart communities train their members to watch for heat exhaustion, heat stroke, and bonking, how to tell the difference, and how to care for people in these situations.

Totally anecdotal but I lost 40 pounds in 4 months with IF and I still worked out 4-5 days a week in the mornings. I found it very very easy to follow and my body had very little trouble adapting

"in the mornings". That's exactly the point.

I eat once a day. I run almost every day. I lift weights at least every other day. I have been doing this for years now.

Our ancestors didn't get three meals a day. Millions of our contemporaries get real physical work done without three meals a day or worrying about glycogen or blood sugar. I may be an extreme example, but people worry way too much about skipping meals, in my opinion. It seems like a rationalization for avoiding hunger.

>Intermittent fasting seems like it'd wreck your body if you do moderate to intense exercise. So I just fasted, and now I want to do intense cardio.... but I might run out of glycogen or blood sugar.

Have you actually tried working out in a fasted state? I find that I get better performance.

Glycogen isn't depleted as quickly as you think, and blood sugar levels are actually more stable in a state of ketosis when your body is manufacturing its own glucose.

>You don't need intermittent fasting to be healthy.

Semantics, but I would say you do if 'intermittent fasting' just means periods of respite between meals so you're not constantly in a 'fed' state. It's only relatively recent in human history that we are even able to be constantly eating.

>Keep your fat, protein, and simple carb levels within reasonable limits for your age, height and sex.

You say this, but experts have all sorts of contradictory recommendations for what are 'reasonable' macro limits.

"Intermittent fasting seems like it'd wreck your body if you do moderate to intense exercise. So I just fasted, and now I want to do intense cardio.... but I might run out of glycogen or blood sugar. Or I may do a set of weight lifting, but not if I can't eat protein after. So if I do intermittent fasting, I have to come up with a complex schedule to follow in order to get any performance gains. "

That's not true. You just have to get used to it. When I did boxing I often did two hours intense workout in the evening and didn't eat anything after or hours before. No problems.

The human body is a stunningly complex evolved system. Intuitive reasoning at a trivial level doesn't really tell you much.

Intuitive reasoning should be suggesting to the parent comment that it would be a huge evolutionary disadvantage if there was no energy available after a short fast.

I participate in IF and lift weights after work most days. I think it's mostly about timing. I'm usually done eating for the day around mid afternoon and feel fine working out after work. You don't need protein after you workout. You will be fine if you get enough protein throughout the day leading up to your workout.

Were you able to sleep without problems? The biggest problem for me was not being able to sleep or waking up in the middle of the night due to hunger.

I just finish a 21 day water fast yesterday - it’s the first time I’ve done it. My sleep was only slightly affected. Not because I was hungry, after 3 days your appetite more or less subsides. The only notable thing that happened as it relates to sleep is that I would only sleep for 5.5 hours and my body would wake up, not groggy or tired. Typically when I eat “normally” I get about 7 hours.

After a couple weeks I stopped thinking about eating until it was time to eat in the morning. Your body gets used to it. You just have to power through the adjustment period.

There's a rather large movement of strength athletes using intermittent fasting as a tool without these issues.

Glycogen stores aren't easily depleted by day to day life, a regular 8 hour window every day wouldn't affect your evening weight lifting routine. It could affect post-workout only by increasing the time for the glycogen stores to be refilled, but not to such an extent that it would affect your next session.

As for protein after workout, this is largely nonsense. The body is more than capable of regulating it's own protein synthesis over the course of days with both the protein you obtain from food and the stores of broken down proteins from your body. Amount of protein consumed (and type) is the relevant factor and timing plays no significant part unless you are a at a level where you are considered a pro athlete and you're probably attending competitions.

"So I just fasted, and now I want to do intense cardio.... but I might run out of glycogen or blood sugar."

I used to think like this, but then I actually tried it and found that not only does a short (16-18 hour) fasted state not negatively impact my workouts but it improves my performance to exercise in a fasted state.

Heavy squat/deadlift day at the gym ... 2 hours of BJJ ... 10 mile run ... these are all examples of things I do in a fasted state. You have no bloodflow diverted to stomach (or other digestive processes) you are fast and light on your feet and your energy is very steady.

Would I embark on a triathlon or an ultra ? Of course not - but whatever fears I had about fasting throwing a monkeywrench into my training were unfounded.

IF is actually a simplifier: skip breakfast. If you don't late-night snack, just skip breakfast and you're doing IF.

I've been skipping breakfast for at least 5 years. Assuming the average breakfast would've cost me 5 minutes per day, I've saved over 160 hours not doing breakfast over those years, never-mind the cost-savings and simplification of life that comes with consuming things less frequently.

I've been healthy and fit the entire time I've been skipping breakfast, maintaining a steady weight of 175 lbs at 6'1". I usually have had caffeine, though I occasionally wean myself off. Caffeine (black coffee, straight tea, no sugar) helps with the hunger/IF lifestyle, but it's by no means necessary.

This gentleman has been doing IF for 5 years and he appears to be doing intense exercise.

https://youtu.be/dW_99QcCTzE

You can lift and do cardio just fine even on full blown water fasting for a couple of weeks, or longer if you're already heavily overweight.

It's not the most pleasant feeling in the universe, and your performance won't be anything to write home about, but you will still be pretty functional. Humans have had to go without food for a while for most of their history, so it makes sense we would have adapted to live just fine through periods of scarcity.

I do IF. I bike to work each day and work out in a gym irregularly. I have either 1 large meal or 2 small meals in a feeding window each day. I will eat right after cycling in the morning, or right after working out. I don't usually eat after cycling at night. I might have some protein or a small cup of milk at night though. Not technically IF, but also not riding that blood sugar wave all the time either.

Nope, it doesn't wreck your body, not even close.

This is because of homeostasis. You normally have close to, iirc, 2000Kcal floating in your blood, intracellular fluid, & cells. If you get too much more, then the pancreas will produce insulin to stimulate your body to store the excess as fat.

But when you are temporarily under-fed as with Intermittent Fasting or Time Restricted diet, the insulin simply doesn't arrive to force it out of the bloodstream so it can maintain the levels; levels can also be restored by converting fat stores to maintain the appropriate blood sugar level.

So, you've always got something like that ~2000Kcal store ready to go, and you don't need to worry about 'bonking' on any normal workout with any normal IF or TR diet.

I personally did once manage to do something like you worry about, during off-season training one year in my career in international-level alpine ski racing. I did a 3-day fast, with a solid weight workout (including big muscle groups) on Day#1. No problem. Then, at the end of fasting Day#3, I felt really energetic, so broke the plan and did another really heavy leg weight workout, which went great. However, about an hour+ afterwards, I felt really wobbly/shaky from low blood sugar. This was fixed with a single big orange juice smoothie. It was really cool to feel it take effect -- within minutes. And, there was no break in the training routine after these events, just continued on as usual.

Admittedly it's a single test, but it shows that it can take a lot more than one workout on a TR or IF day to even get to an out-of-the-ordinary state, and it's easily fixed when you do. Not really anything to worry about.

[Edits - clarity, commas]

Perhaps IF will allow you to complete your workout but with no where near optimal performance.

I got stronger and was able to run longer and further when I ate one meal a day. I went from a slow 1 mile run to fast 2 mile run and ended up at 3 miles by the end of one month.

Plan better. If you don't like to train fasted, then plan your fasting / workouts for an hour after you eat. That way you can also have a post workout meal.

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