The Starvation Hormone
If you are on a strict diet, after as little as 48 hours, your body will recognise this and produce a 'starvation hormone' that will cause your metabolism to drop and thereby make it even more difficult to lose weight. Furthermore, when you stop dieting, it will mean that you cannot return to your previous consumption rates of food without putting the weight back on rather quickly because your metabolic rate has been lowered through dieting. You also run the risk when you are dieting if you don't do strength training of losing muscle tissue. For every pound of muscle that you lose, your metabolism can drop by as much as 50 calories a day.