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It seems to be a relatively well-known fact that sudden extended periods of caloric restriction will cause a severe drop in metabolism. But I can't seem to find much research about the reverse process. So the question is, does it work the other way too?

The basic scenario I'm asking about is if one were to go from a lifestyle of plenty of exercise, and a high-calorie diet to compensate (if you need more detail, say the diet consists of plenty of proteins, decent fats, relatively-low carbs, so quite healthy) to a lifestyle of no exercise, half the calories, much more carbs, much less protein. Current evidence seems to indicate this would cause a significant drop in metabolism.

So what about the inverse scenario? Say after six months, our subject adds back the exercise, and doubles calorie consumption by switching back to a diet of plenty of proteins, decent fats, and relatively-low carbs. Say this change takes place over a single week, and remains afterward.

Would this sudden change result in a rapid increase in metabolism, similar in magnitude to the rapid decrease caused by the inverse, and would it last? Is the body more conservative with increases in metabolism than with decreases? What would be the effects on the body?

Disclaimer: I realize "metabolism" is non-technical shorthand for the convergence of thousands of chemical processes used by the body to essentially process energy, and that the changes above would result in complex chains of changes that can't be exactly predicted. I'm not trying to calculate exactly what would happen, just get a general sense of how this process reacts to changes.

  • This question is good, but impossible to answer. The response to the 'stimulus' depends on gender, age, diet (including when you eat), type of exercise, genetic disposition, sleeping pattern, etc. – jiggunjer May 22 '15 at 12:48
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    Regular aerobic exercise does shift basal metabolism towards a higher caloric consumption at rest. – Centaurus Dec 26 '16 at 14:53
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If a person's body is in a low-metabolism state induced by starvation or restricted calorie intake, then an increase in the calorie intake will allow a raised metabolism. The natural lower limit to metabolism is death: if a person restricts calories too much, their metabolism drops lower and lower, until they develop various complications and then die. The natural upper limit to metabolism is, in my view, heat: a person's metabolism is only going to increase naturally to a certain point, based on their BMI, body composition, genetics, lifestyle, etc., and after that point the metabolism will not increase any more otherwise excessive heat would be generated (also leading to death.) A example of dysfunctional metabolism where people just burn more and more energy is the misuse of the now-unavailable drug mimicking "uncoupling protein" (http://www.independent.co.uk/news/uk/home-news/death-of-medical-student-sarah-houston-after-taking-banned-slimming-drug-dinitrophenol-highlights-8584597.html). BUT this is an example where a drug was taken that dysregulated metabolism. Normally the body will not allow the metabolism to increase like that. What happens instead in the natural world is obesity. If you increase calories too much, past the point of metabolic increase, then extra calories are stored as fat and you become obese.

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