why diets don't work....

For the Overweight, Bad Advice by the Spoonful

scientists recently have come to understand that the brain exerts astonishing control over body composition and how much individuals eat. “There are physiological mechanisms that keep us from losing weight,” said Dr. Matthew W. Gilman, the director of the obesity prevention program at Harvard Medical School/Pilgrim Health Care.

Scientists now believe that each individual has a genetically determined weight range spanning perhaps 30 pounds. Those who force their weight below nature’s preassigned levels become hungrier and eat more; several studies also show that their metabolisms slow in a variety of ways as the body tries to conserve energy and regain weight. People trying to exceed their weight range face the opposite situation: eating becomes unappealing, and their metabolisms shift into high gear.

The body’s determination to maintain its composition is why a person can skip a meal, or even fast for short periods, without losing weight. It’s also why burning an extra 100 calories a day will not alter the verdict on the bathroom scales. Struggling against the brain’s innate calorie counters, even strong-willed dieters make up for calories lost on one day with a few extra bites on the next. And they never realize it. “The system operates with 99.6 percent precision,” Dr. Friedman said.

The temptations of our environment — the sedentary living, the ready supply of rich food — may not be entirely to blame for rising obesity rates. In fact, new research suggests that the environment that most strongly influences body composition may be the very first one anybody experiences: the womb.

According to several animal studies, conditions during pregnancy, including the mother’s diet, may determine how fat the offspring are as adults. Human studies have shown that women who eat little in pregnancy, surprisingly, more often have children who grow into fat adults. More than a dozen studies have found that children are more likely to be fat if their mothers smoke during pregnancy.

The research is just beginning, true, but already it has upended some hoary myths about dieting. The body establishes its optimal weight early on, perhaps even before birth, and defends it vigorously through adulthood. As a result, weight control is difficult for most of us. And obesity, the terrible new epidemic of the developed world, is almost impossible to cure.