What You Can Change _. And What You Can't - Martin E. Seligman [93]
In one study, the “lucky” 10 percent of formerly fat people who dieted and stayed thin ate an average of 1,298 calories a day to stay at their new weight, whereas normal controls ate 1,950 calories to stay at that same weight. This demonstrates that dieters may never again be able to eat normal amounts of food if they want to stay thin. Yo-yo dieting—taking weight off, putting it all on again, and then trying to take it off once more—is a Sisyphean battle. The second time obese patients go on a VLCD, they lose weight more slowly, yet they take in exactly the same number of calories as the first time.15
This makes biological sense. Imagine a species only recently emerged from 100,000 years of famine. During this epoch, weeks or even a whole season go by with almost nothing to eat. Then there is a big kill or a bumper crop. Everyone gorges and then rations what is left until the next big kill. An epoch of famine and feast produces strong evolutionary pressure for a creature who gorges and stores up a lot of fat during periods of plenty, but releases fat’s life-sustaining energy with reluctance during shortages. The more the creature goes through the feast-famine cycle, the better it gets at storing fat and conserving energy.
Now imagine that this epoch suddenly ends and food is abundant. This creature eats a great deal and gets fat. Someone conceives a scheme to limit fat, and the creature voluntarily undereats. But its body can’t tell the difference between self-imposed starvation and actual famine. So the hoary survival defenses kick in: The body defends its weight by refusing to release fat, by lowering its metabolism, and by insistently demanding food. The harder the creature tries not to eat, the more vigorous these defenses become.16
This creature is Homo sapiens, the departed epoch is the Pleistocene, the time is now, and the doomed scheme is dieting.
Bulimia and Natural Weight
A concept that makes sense of your body’s vigorous defense against weight loss is natural weight. When your body screams “I’m hungry,” slows its metabolism, makes you lethargic, stores fat, craves sweets and renders them more delicious than ever, and makes you obsessed with food, what it is defending is your natural weight. It is signaling that you have dropped into a range it will not accept. Natural weight prevents you from gaining too much weight or losing too much. When you eat too much for too long, the opposite defenses are activated and make long-term weight gain difficult. A group of prisoners was paid to add 25 percent to their body weight by eating twice their usual calories for six months. The first few pounds came on easily, but then there was no weight gain.17
There is also a strong genetic contribution to your natural weight. Identical twins reared apart weigh almost the same throughout their lives. When identical twins are overfed, they gain weight and add fat in lockstep and in the same places. The fatness or thinness of adopted children resembles their biological parents—particularly their mother—very closely, but does not at all resemble their adoptive parents. This suggests that you have a genetically given natural weight that your body wants to maintain. I don’t know a formula for assigning a number to your natural weight, but it is probably considerably higher than your “ideal” weight. The average middle-aged American man, for example, weighs 16 percent more than his “ideal” weight.18
The idea of natural weight may help cure the new disorder that is sweeping young