You've probably heard of the calorie-restriction diet: You eat at least 30 percent fewer calories than normal humans, about 1,750 instead of 2,500 for an adult male. If you keep yourself on the verge of starvation, CR devotees claim, you can extend your life span past 100 years, perhaps 120. (The theory is that the body switches into an emergency defensive state and slows your metabolism, producing fewer cell-damaging free radicals.)
A few years ago, I tried the CR diet for a book I was writing about health. I spent hours a week filling in spreadsheets with apple calories, weighing food, and watching friends eat. I was perpetually hangry, though CR fans say that you get used to it. In fact, you start to love it. You feel energized. "I literally get high from it," said one CR expert I visited.