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Comment by JumpCrisscross | Hacker News Reader

A fat person works harder exercising than a fit person. Their hearts and digestive systems are constantly working harder, and they’re wasting energy on inflammation. By losing weight, they can both increase their activity level and decrease their calories in and out.

We know calorie restriction + exercise works in mice. So this isn’t a thermodynamic problem. We in tech tend to think from first principles; calories in = calories out seems obvious. The problem is it’s misleadingly simplifying—there is a lot in between that is significant.

In any case, I don’t think this is therapeutically inclined. It’s simply hinting at an underlying mechanism we may be able to exploit.

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> A fat person works harder exercising than a fit person.

Primarily because of improper muscle activation, and from their body weight making the exercise more intense.

Athletes increase their cardiovascular and metabolic throughput (i.e., allowing them to burn even more calories and thus work even harder), and repeating an activity increases muscle control, allowing more coordinated and balanced movements (e.g., keeping themselves and external weights balanced without erratic, wasteful compensatory movements). They might also have a diet that absorbs better, as athletes try to absorb absurd amounts of calories.

A larger person does have a higher base energy consumption, although this is not caused by inflammation - it's just that any tissue need energy. If this was not the case, even just a few kilocalories overeating would cause unbounded growth - instead, energy requirements for a person lie on a curve, and slight overeating for one body weight just means that you reach equilibrium at a slightly higher body weight, with any combination of food intake + activity + body composition having some (although possibly absurd) body mass equilibrium. Of course, being morbidly obese does introduce high risk of certain diseases that have an energy cost and waste (e.g., mismanaged diabetes and sugar in urine), but I consider that somewhat separate.

Caries in = calories out is a thermodynamic problem. Thermodynamics account for inefficient processes. If you take fewer calories in, it always means that your body will be doing less or taking its energy from elsewhere. The body has plenty of ways to do this, including reducing base metabolism at certain costs. The sheer number of backup plans the body has available for any particular function is fascinating, but they are generally all costlier than the primary ones.

However, do not let that deter you from exploring this further. Collecting data on health outcomes of human behaviors is almost impossible without massive datasets - can't exactly cage people up in labs to test them.

> Thermodynamics account for inefficient processes

Not arguing it doesn't. Just that using thermodynamics to understand human metabolism is akin to trying to grok flight through Newtonian mechanics. You can do it. But mostly by working backwards from higher-level principles.

The evidence for that disconnect is this thread. CACO leads people to believe you can't decrease your calorie consumed and burned without also increasing physical activity levels. Yet that's empirically incorrect. Not because thermodyanmics doesn't apply. But that it applies in mechanisms so complex that starting from first principles doesn't work until you have the roadmap.

> slight overeating for one body weight just means that you reach equilibrium at a slightly higher body weight

Studies observing the effects of calorie restriction see improvements in a variety of biomarkers. That slightly-higher weight comes with higher inflammation, higher CVD frequencies and other nasties.

And more practically speaking the relationship is assymetric. It's significantly more practical to restrict calorie consumption than to burn the equivalent level of calories through exercise (even without considering the impact it has on appetite and on the mind, where you think you deserve to eat more as a result).

Well... I could argue.

Based on my personal experience, whether you exercise or not you are still going to be miserable when on caloric restriction.

But when you are exercising your portions do not get so small. In fact, you could be eating exactly the same and if you add walking about 10km (6 miles) every day, you are putting yourself in a significant calorie deficit of about 600 kcal (adult male, regular height, a bit overweight).

While it does not matter where 600kcal deficit comes from from thermodynamic point of view, it makes dieting easier:

* The food portions have the size you are used to. Your stomach is used to about this kind of food. At least some satiety signals are going to be the same as before you started dieting.

* Exercising will preserve muscle mass. We have a mechanism where if the body needs to access stored energy it will spare the muscles that are being exercised. This is how bodybuilders are cutting -- during cutting phase they are reducing their fat without building new muscle but are still exercising. This exercising is necessary so that the body burns fat preferentially rather than going for muscle protein.

* Exercising seems to prevent most or all of BMR drop from calorie restriction. Normally, if you just reduce your calories without much activity, the body will start conserving energy in various ways (for example I felt cold on hot days which was super interesting feeling). If BMR drops, you need to reduce your food intake even further to ensure the same level of calorie restriction. And if you do not do this you might find that a) you have reduced your calorie intake and b) you are not losing weight. Terrible place to be in. Activity prevents that from happening.

Your points are all valid, you've perhaps convinced me to give it a go again. Only thing I'd add is walking for 2 hours in total a day every single day is hardly feasible.

I just checked my Garmin progress reports. In April I injured my foot and could not run but could walk and so while I was recovering I started walking a lot to replace and later supplement my running.

Over the period of six month from May 2023 to October 2023 I logged:

* 2497km of combined walks and runs (about 80% walks and running the rest), about 13.6km a day on average

* 384h of activities (for about 2h 7m daily average)

* about 6.5km/h average activity speed. I walk at about 6km/h normally (sometimes faster, sometimes slower), some of the activity time is probably walking into groceries or standing in a queue for a coffee and some of the activities are runs.

* 709k steps in May * 775k steps in June * 792k steps in July * 808k steps in August * 713k steps in September * 618k steps in October

For a total of 4.4M steps in 6 months or about 24.2k steps a day, on average.

* as an interesting note, Garmin estimates that my activities burned 180 thousand kcalories which translates to 20kg of pure fat or about 23kg of adipose tissue (I have maintained my weight during that period, though). Hard to say how accurate this is.

So, yes, it is feasible. Though quite time consuming. I switched my entertainment needs to consuming audiobooks and whatever informational/educational content I could put my hands on that would be even remotely useful.

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