No Better Health Bargain
Weight loss was not the point of the study; the WHI is evaluating the effect of a low-fat diet on breast and colorectal cancer. "But a major dietary intervention study like this with such modest weight change underscores the dismal track record of failure to find dietary interventions that promote long-term weight loss," says Dansinger. Barbara Howard, president of the MedStar Research Institute, who led the WHI study, sees it differently. She was encouraged that some women increased their servings of fruit and vegetables to five a day, and notes that those were the women who lost the most weight. "It's hard for people to make changes," says Howard. "We need to be realistic in terms of what dietary modifications are possible."
Biology seems to work against long-term weight loss. Michael Rosenbaum, an associate professor of clinical medicine at the Columbia College of Physicians and Surgeons, believed leptin, a hormone secreted by fat cells, might be the culprit causing weight regain after dieting. "When your leptin level is low for you--and it's different for everybody--your body reacts by lowering your energy expenditure, increasing the efficiency of your muscles, and favoring restoration of leptin levels to their usual values," says Rosenbaum. That seems to trigger the weight return.
And there is no evidence that a previously fat body ever becomes accustomed to the drop in leptin. Rosenbaum points to the successful losers in the ongoing National Weight Control Registry, some 5,000 people who have lost 30 pounds or more and maintained the loss for at least a year. Registry participants used every imaginable diet. But maintaining their losses is a major effort. Most eat a low-calorie, low-fat diet, record food intake, and exercise an hour a day or more to override their bodies'biological drive to regain. "A person who maintains even a small degree of weight loss has done an amazing thing," Rosenbaum says. "Evolution favors fatness."
Diet yo-yo. That may be why some research indicates that frequent dieting leads to weight gain. In a 2004 study in the Journal of the American Dietetic Association of 149 obese women, those who had dieted before age 14 were more than twice as likely to have dieted 20 times or more and had the highest BMIs. The vast majority of the women, 79 percent, had not been able to maintain any permanent weight loss, though 9 percent kept off a loss of 20 pounds or more. Joanne Ikeda, a nutrition specialist at the University of California-Berkeley and the lead author of the study, says that these women had become very vulnerable to yo-yo dieting, which often leads to higher permanent weights. "There is a subset of people," says Ikeda, "and we can't identify those people yet, but their bodies become more and more efficient at fat storage and they become less able to take weight off."
Still, neither biology nor yo-yo dieting tells the whole story. Genes also play a role. Older studies of twins estimated that as much as 70 percent of adult body weight is inherited. In a 2004 study, James Romeis, a professor of health services research at St. Louis University, looked at the weight of Vietnam War-era twins who were at normal weight when they entered the military and gained as they grew older. "You end up with about 50 percent of weight gain or weight change being genetically influenced," Romeis says. "So, if you were born with the genes that contribute to weight gain, then you've got to work doubly hard to take it off."
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