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Just because it boosts GH doesn't mean you build muscle. Undoubtedly, fasting has positive metabolic benefits, but building lean muscle mass isn't one of them. The studies I have seen about regular fasting and muscle mass generally show loss or at best maintenance with exercise. Generally you will be catabolising muscle when you wake up from sleeping, until consuming sufficient protein. This is why body builders eat so often, and also try to have some slow release protein before sleeping.

You are right that exercise isn't a good way to lose weight, I am not talking about that at all. By magnitude of benefit I am talking about mortality/longevity/frailty, not weight loss. That's what really matters.

The relationship between body weight and hard clinical outcomes is complicated and not monotonic (obese pre-menopausal women are less likely to get breast cancer, to provide one example). Additionally, asian people suffer from the skinny-fat phenomenon, where they are not obese but have metabolically pernicious visceral fat.

The post you are responding to does not make the claim that it builds muscle, nor does it make reference to lean muscle mass... It says "preserves" muscle (comparable to "maintenance" as you suggested).

I'm not buying it. Muscles use energy even while at rest so in the case of an emergency I'm sure the body will first remove the useless consumption of unnecessary muscle mass than to start tapping the reserves.

In what world would the body prioritize consuming "unnecessary muscle mass" (the thing you need to hunt down and kill food) over fat, which is by definition energy stored for this exact scenario?

Muscle simply doesn't consume much more energy at idle than fat does but is far more useful and far less calorie-dense. A pound of muscle burns 4-6 calories per day at idle vs a pound of fat which burns 2-3 calories. Basically the same.

>In what world would the body prioritize consuming "unnecessary muscle mass" (the thing you need to hunt down and kill food) over fat, which is by definition energy stored for this exact scenario?

I would predict that the body would consume both, in a ratio that shifts from fat towards muscle as energy supplies dwindle, in an attempt to stretch the final reserves by reducing consumption.

HGH promotes breakdown of fats [1] and inhibits the breakdown of muscle [2]. Since fasting significantly increases HGH, that would all make sense.

[1] https://pubmed.ncbi.nlm.nih.gov/11086655/

[2] https://diabetesjournals.org/diabetes/article/50/1/96/10905/...

>in a ratio that shifts from fat towards muscle as energy supplies dwindle

it's in fact the other way around. The body first reduces what is not used (unused muscles) and then energy reserves.

[citation needed]

>citation needed

common sense

Try to build some muscle and get shredded... should be very easy with your methode/logic

With respect 'common sense' is frequently wrong which is why I was asking for some study, evidence, documentation etc. Along the lines of the articles I provided.

If you just want an anecdote it certainly works for this guy [1]. And he, in turn links out to a ton of studies.

To be clear at no point did I claim that fasting would grow muscle, I don't have any data to back that up. What I said was that your body will preserve muscle when fasting because muscle is useful and fat is not. This is backed up by the articles I cited indicating significant HGH increase, and articles citing the role of HGH as inhibiting the breakdown of muscle and promoting the breakdown of fat.

Your claim requires evidence.

[1] https://leangains.com/

Original GP quote:

> Otherwise, as far as health interventions go, exercise has a much larger magnitude of benefit than dietary interventions.

Note that GP doesn’t mention weight loss, only health in general. To push further on this point, many studies came with the conclusion that exercice had more impact on health than dieting (subjects wouldn’t lose weight, but get healthier)

e.g: https://www.cell.com/iscience/fulltext/S2589-0042(21)00963-9

> Fasting is the simplest nutrition science there is. BMR 2000kcal? Don't eat for a day, lose 0.6lbs.

And there are additional benefits aside from basic weight loss. Fasting for a day every once in a while should be regular behaviour. Some religions sort of get it and there are versions of fasting in most major religions. But for basic weight loss, it's very simple. Stop eating so often, stop eating so much, stop eating garbage. Unfortunately it's not easy.

>Humans are well known for compensatory eating

True, but this applies to fasting as well as exercising (if not more so)!

At the end of the day, what matters most for fat loss is changing your habits. I don't think that "calories in / calories out" has been invalidated, so you have two sets of habits you can adjust. If it is easier for you to reduce calories in with fasting vs. portion control, then go for it.

IME it is incredibly painful to miss a meal, but not so painful to eat less calories when I do eat - particularly if I substitute high density carbs (bread, pasta, sugar) for lower density (veg, etc).

I do think that just focusing on calories out is problematic for the obese and/or long term sedentary - mainly because they are way more likely to injure themselves by not ramping up to activity very carefully...

> IME it is incredibly painful to miss a meal.

Like anything it takes practice! Day two is usually the worst but then hunger basically zeroes out and doesn't come back until ... well, ever. Apparently it returns once you run out of fat stores, but I never got that far. You get cravings once in a while, but not hunger.

But exercise increases your muscle mass, which raises your basal metabolism, doesn't it? How big is that effect? Seems like it should be quite big, but I have no data and seldom see it discussed, as if it didn't matter at all.

But then why do we lose muscle mass if we don't exercise? Seems like it would be a huge maladaptation if muscles were "cheap".

Musculature alone doesn't increase basal metabolism by a lot. At least not the muscles gained from typical light exercise stuff. It's a combination of maintaining them and exercise that gets you maybe an extra 300-500 a day average.

Muscle mass also isn't lost as quickly as people claim. It varies based on person and diet. You lose some, but many can get back to their former peak in a few weeks if it has been a year or so. Even fairly muscular individuals.

> An average human burns like 100kcal per mile running

This is not true, and it’s far off the mark for those who are overweight.

An average human isn't overweight enough to make this matter. That's why it's an average.

For a morbidly obese person they burn more calories standing up and walking around the house than I do. The thing is once you're past this phase of being overweight or obese your caloric expenditure drops precipitously. When I was working out 4 days a week my body adapted such that my caloric consumption had to go from 3200 calories a day to 2500 calories a day to maintain weight.

Running is not an efficient way to burn fat. It never has been, and never will be. The reason marathon runners are so rail-thin is because they run a lot. Running preferentially burns muscle as well due to the quickness of conversion after glucose is gone. Worse yet, there's no increase in calorie burn via muscle gain and hormone stimulation. It's just a flat consumption of calories.

In summary: being overweight is an edge case and not an average. Any mildly trained person will realize a drop in overall calorie expenditure as their body adapts to exercise. This is why modern exercise science emphasizes "confusion". Otherwise you plateau (and pretty hard, usually).

> The reason marathon runners are so rail-thin is because they run a lot. Running preferentially burns muscle as well due to the quickness of conversion after glucose is gone.

I think there's some selection bias to this though. The morbidly obese tend not to be marathon runners, as well as the very muscular. Marathon running is an extreme activity that preferentially self selects certain physical attributes and conditions. This is not to say that a morbidly obese person can't take up marathon running - but they unlikely to be able to maintain it successfully while remaining so.

> A general estimate for calories burned in one mile is approximately 100 calories per mile, says Dr. Daniel V. Vigil, an associate clinical professor of health sciences at David Geffen School of Medicine at UCLA.

But sure it varies by weight. That said, the super-overweight are also too out of shape to run anywhere close to the required distance.

[1] https://www.healthline.com/health/fitness-exercise/running-b...

> Not sure why that would be expected. Fasting leads to significantly increased levels of HGH which preserves muscle and improves body composition.

If you lose a lot of weight, that means that your muscles have to work less to move all that weight around.