Most people are so familiar with the dangers of overeating that they never stop to think how odd it is that the human body can make such a colossal blunder. After all, the body is usually a miracle of self-regulation. Spend all day at the gym, and you still won’t end up with more muscle than you can carry around (unless you dose up on steroids). Shower every hour, and you still won’t end up with skin that’s six inches thick. But scarf a few dozen extra Twinkies, and you just might end up saddled with a sizable spare tire of fat. Clearly a better-designed body would compensate for this mistake by jettisoning extra calories. After all, few humans can use an extra 100-pound energy reserve. A more intelligent body would reach a set fat threshold and then stop accumulating any more. But the human body never developed this skill because it never found itself in this situation— until now.
Tens of thousands of years ago, it was critical that our ancestors ate every calorie that came their way. Obesity—the result of being able to find and eat vastly more of the nutrients that you need to survive in a harsh, physically demanding world—was virtually impossible. (In fact, it’s only in the last 50 years that scientists have collected worldwide obesity statistics—until then, obesity seemed like the relatively rare problem of a few compulsive eaters.) Your genes have been passed down from the most successful humans in those prehistoric days, and they had bodies that craved all the food they could get.
In other words, the sweeping timescale of evolution has honed your appetite-control system into a powerful force for preventing starvation—not for managing weight. If it’s any comfort, blame the cavemen. If they had found a way to eat themselves to diabetes and coronary heart disease 50,000 years ago, the forces of evolution would probably have solved the problem by now.
Source of Information : Oreilly - Your Body Missing Manual