T Nation

How Does Cal Restriction Affect BMR?

  I'm fresh out of school with a degree in exercise science, so i SHOULD know this..

If you restrict your caloric intake, does the body respond by lowering BMR (slowing metabolism)? Consequently, if you up your caloric intake, does your body respond by increasing your BMR?

yes and yes. but not to the degree many people believe. The greatest adaptive metabolic slowdown ever recorded was ~15%. This occurred after month and months of starvation (50% maintenance) and only when bodyfat levels got critically low, ~6% if I recall

of course, the degree to which a metabolism will adapt to energy intake is highly dependent on the individual

It will take extended periods of time of caloric restriction (usually quite a bit as well) for one’s RMR to be effected.

This is one reason crash diets or VLCDs (very low calorie diets) aren’t recommended, even more so for extended periods of time.

If you increase your caloric intake and build muscle, then yeah RMR should increase.

Yes and yes. Think about it, if you’re eating less calories your body will sense that food might be scarce (it obviously isn’t in our society) so it will signal different hormones to do certain things and this will lead to a lower BMR (probably through less T3 or T4 being produced by the thyroid).