Over time, the human body became remarkably good at guarding its energy reserves through complex biological defenses wired into the brain. As we found in our recent research, our brains also have powerful mechanisms for defending body weight – and can sort of “remember” what that weight used to be. For our ancient ancestors, this meant that if weight was lost in hard times, their bodies would be able to “get back” to their usual weight during better times. The fact that our bodies have this capacity to “remember” our previous heavier weight helps to explain why so many people regain weight after dieting. Research is also showing that good health isn’t the same thing as “a good weight.”