I am currently reading a book called "The Body Sculpting Bible for Men" by James Villepigue and Hugo Rivera. In it the author claims that when you start dieting your body receives a shock from the immediate decrease in calories and you lose weight fast. After about two weeks the shock wears off, your body becomes accustomed to the change in diet. It starts to slow down metabolism to conserve energy since the caloric intake is lower now. So instead of continuing to lose fat you just become more lethargic and the fat stops burning. He claims the same thing about exercise routines. Stating that both diets and exercise regimens need to be changed up every couple of weeks to make sure the body doesn't get accustomed to either. For example he suggests that you alternate between high and low calorie diets biweekly. Only in this way can one lose weight and gain muscle consistently.
Is this true?