The trouble with the science of obesity as it has been practiced for the last sixty years is that it begins with a hypothesis—that “overweight and obesity result from excess calorie consumption and/or inadequate physical activity,” as the Surgeon General’s Office recently phrased it—and then tries and fails to explain the evidence and the observations. The hypothesis nonetheless has come to be perceived as indisputable, a fact of life or perhaps the laws of physics, and its copious contradictions with the actual observations are considered irrelevant to the question of its validity. Fat people are fat because they eat too much or exercise too little, and nothing more ultimately need be said.

The more closely we look at the evidence and at obesity itself, the more problematic the science becomes. Lean people will often insist that the secret to their success is eating in moderation, but many fat people insist that they eat no more than the lean—surprising as it seems, the evidence backs this up—and yet are fat nonetheless. As the National Academy of Sciences report Diet and Health phrased it, “Most studies comparing normal and overweight people suggest that those who are overweight eat fewer calories than those of normal weight.” Researchers and public-health officials nonetheless insist that obesity is caused by overeating, without attempting to explain how these two notions can be reconciled. This situation is not improved by the prevailing attitude of many nutritionists, obesity researchers, and public-health authorities that it is evidence of untoward skepticism to raise such issues, or to ask questions that lead others into contemplating the contradictions themselves.

For the past decade, public-health authorities have tried to explain the obesity epidemic in the United States and elsewhere. In 1960, government researchers began surveying Americans about their health and nutrition status. The first of these surveys was known as the National Health Examination Survey. It was followed by an ongoing series of National Health and Nutrition Examination Surveys (NHANES), of which there have been four so far. According to these surveys, through the 1960s and early 1970s, 12–14 percent of Americans were obese. This figure rose by 8 percent in the 1980s and early 1990s, and another 10 percent by the turn of this century.

This doubling of the proportion of obese Americans is consistent through all segments of American society, although obesity remains more common among African Americans and Hispanics than among whites and other ethnic groups, and most common among those in the lowest income brackets and poorly educated. Children were not exempt from this trend. The prevalence of overweight in children six to eleven years old more than doubled between 1980 and 2000; it tripled in children aged eleven to nineteen.*65