Originally Posted by dyna mo

from the book re: metabolism-

So when you start dieting, eating less and losing bodyweight, your hypothalamus senses it and your body slows metabolism, increases your hunger/appetite levels, and alters hormone levels in a generally negative fashion. To a much lesser degree, when you overeat and start gaining weight, your hypothalamus increases metabolic rate, decreases your hunger/appetite, and ramps up certain hormones.

So when you start a diet, eating less and losing weight, your body notices it and starts to adjust metabolism downwards.

This ties in with the information on metabolic slowdown that I presented in the last chapter. As I made reference to, how hard and how fast metabolism tends to crash on a diet depends on a lot of factors including gender and genetics (neither of which we can control). But one of the main ones is initial bodyfatness: fatter individuals can usually diet longer without needing a break from the diet (both a psychological and physiological break) than leaner individuals. So once again your diet category will determine how long you can and/or should stay on the crash diet: the lower the category, the less time you should be on the diet before taking a break of some sort.