There's also the concept of baseline and highly adaptability to continued circumstances, so presumably metabolism is highly elastic if gradually tuned over the years.

Diets don't cause low metabolism, except in the sense that when you lose weight it takes fewer calories to keep the remaining smaller amount of tissue alive. So as you lose weight, in order to continue losing weight at the same rate you have to keep cutting calories even further.

That the "basal metabolic rate" slows down when dieting is shown by many studies on diet. The weight loss isn't linear and slows down over time, in about 6 months or so, even if the caloric deficit is sustained. Not only that, but the basal metabolic rate stays low even after people start eating normally again.

Here's a study: https://www.ncbi.nlm.nih.gov/pubmed/18842775

Here's another one: https://www.ncbi.nlm.nih.gov/pubmed/23535105

Another interesting finding is what happened with the Biggest Loser contestants: https://www.scientificamerican.com/article/6-years-after-the...

That group on average burned 2607 before the competition, but only about 2000 calories after the competition, even if they continued to do plenty of exercise afterwards. They also regained much of that lost weight.

Thin people shouldn't be giving dieting advice, because the obvious confounder is having a well functioning metabolism, whereas overweight people don't ;-) This is made worse by doctors doing it for the same reasons as everybody else. Until they get fat themselves, realizing only afterwards that gluttony wasn't the problem after all.

You've misinterpreted most of the research. The "Biggest Loser" study has been debunked. https://renaissancehumans.com/biggest-loser-study-calorie-re...

The concept of a damaged metabolism doesn't make sense. Your body doesn't waste energy for the hell of it, there is not even a dial for the metabolism to change. Your organs just perform their functions using energy in the process. An organ can't reduce its energy expenditure without compromising its function. Not to mention that if it were possible to live with less calories, evolution would have eked out that benefit millions of years ago.

It is well known that the resting energy expenditure is a simple function of body composition, with no influence of age, gender or body weight [0]

The first study attributes the drop in energy expenditure to the non-resting energy expenditure, which isn't part of the metabolism. There is no saying that difference in energy expenditure isn't compensated for in real life situations, the study freely admits the difficulty in controlling for it.

The second study shows a drop of energy expenditure of a whopping 2%. Another explanation of the effect could just be that the formula they use to predict the resting metabolic rate is too simple, it literally only uses two variables: fat mass and fat free mass. You wouldn't expect such a simple formula to hold over a wide range of weights, it's surprising that it works so well, to within 2%, in the first place.

The third one, the Biggest Loser study, is the only one of the three that is just plain wrong. I'm very surprised to see it appear on Scientific American. In the study, they invent their own formula for the RMR by doing a multilinear regression in 4 variables on 14 subjects. This formula is different from the usual formulae and tellingly underestimates the caloric need of fat tissue (1.5 kcal/d/kg instead of 3.5 kcal/d/kg or 5.7 kcal/d/kg as in your second study). Then they apply that formula, which was calibrated only on the obese subjects, on the people after they lost weight and compare that to the measured RMR, instead of using a more standard formula, and interpret the difference as metabolic damage. No wonder it doesn't work. If you instead plug in the data in a more accepted formula, you see little difference with the measured metabolic rate. Heck, even I have massive metabolic damage according to that formula, their formula estimates my RMR at a whopping 2460 kcal/d, which isn't my total daily energy expenditure. The measured RMR in the article, 1903 kcal/d, wouldn't be unusual for people of that weight.

That study should have never gotten past peer review, and I don't know why it hasn't been retracted yet.

I don't understand the focus on metabolism anyway. Even if a damaged metabolism existed (it doesn't), that still wouldn't change anything if you ate less. The problem lies in a miscalibration between satiation and energy need, we should be figuring out why some people are more hungry than others, and what we can do to change that.

0: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3139779/

> Not to mention that if it were possible to live with less calories

you don't think eg amenorrhea features?

Doesn't that go in the face of this study?

That is, this study seems to claim that what you eat can impact your metabolism.

No. With a diet the metabolism go much slower.

https://www.scientificamerican.com/article/6-years-after-the...