Today, at the start of the new year, millions of Americans will resolve to lose weight, but by tomorrow, or next week, or maybe next month, most of them will have given up trying. Few will have lost weight, and even fewer will sustain the loss. Still, at any given time of the year, an astonishing 15 to 35 percent of Americans are trying to lose weight. They buy low-calorie and low-fat foods, deny themselves desserts, drink only artificially sweetened beverages, join commercial weight-loss clubs (and buy their special and especially expensive prepared meals), visit "fat farms," take diet pills of one sort or another, submit to liposuction, and exercise obsessively to burn calories. Every new remedy is greeted with a wave of enthusiasm, from amphetamines and thyroxine in the 1960s to Olestra, fenfluramine and phentermine (fen-phen), and now sibutramine in the 1990s. The goal is to reach the elusive American ideal -- to be slim, fit, and forever young.
But there is a dark side to this national preoccupation. Since many people cannot lose much weight no matter how hard they try, and promptly regain whatever they do lose, the vast amounts of money spent on diet clubs, special foods, and over-the-counter remedies, estimated to be on the order of $30 billion to $50 billion yearly, is wasted. More important, failed attempts to lose weight often bring with them guilt and self-hatred. After all, even overweight people are likely to share common prejudices about themselves as lazy, undisciplined, and self-indulgent. To add injury to insult, the latest magical cures are neither magical nor harmless. Olestra causes a loss of essential nutrients; dexfenfluramine is associated with potentially fatal pulmonary hypertension; and fen-phen may be associated with serious valvular disease of the heart.
As common as efforts to lose weight are in the general population, they are virtually ubiquitous among adolescent girls and young women. In middle schools, high schools, and colleges throughout the country, girls who are far from overweight believe they are obese, or "gross." They often adopt bizarre diets, starve themselves, take laxatives, or binge and purge. Anorexia and bulemia are epidemic in this population -- and dangerous, with a mortality rate as high as 20 percent. Although many girls caught up in these practices are well aware of the hazards, they would rather risk death than fall short in their attempts to attain the contemporary esthetic ideal of extreme thinness.
Given the enormous social pressure to lose weight, one might suppose there is clear and overwhelming evidence of the risks of obesity and the benefits of weight loss. Unfortunately, the data linking overweight and death, as well as the data showing the beneficial effects of weight loss, are limited, fragmentary, and often ambiguous. Most of the evidence is either indirect or derived from observational epidemiologic studies, many of which have serious methodologic flaws. Many studies fail to consider confounding variables, which are extremely difficult to assess and control for in this type of study. For example, mortality among obese people may be misleadingly high because overweight people are more likely to be sedentary and of low socioeconomic status. Thus, although some claim that every year 300,000 deaths in the United States are caused by obesity, that figure is by no means well established. Not only is it derived from weak or incomplete data, but it is also called into question by the methodologic difficulties of determining which of many factors contribute to premature death.
Nevertheless, the totality of evidence suggests that as weight increases, so does mortality, but only modestly. The usual measure of leanness or fatness is the body-mass index, calculated by dividing the weight in kilograms by the square of the height in meters, and the optimal body-mass index is usually considered to be about 21.0. Above that level, the risk of death increases little until a body-mass index of about 27 or 28 is reached. Translated into familiar terms, a body-mass index of 27 to 28 corresponds to a weight of 162 to 168 lb (74 to 76 kg) for a 5'5" (165 cm) woman and 188 to 195 lb (85 to 89 kg) for a 5'10" (178 cm) man. Only for those with a body-mass index well above 28 does the relative risk of death reach 2.0. Furthermore, the association is highly age-dependent, as shown by Stevens et al. elsewhere in this issue of the Journal. It declines steadily with age until about 74 years, after which there appears to be no correlation between body-mass index and mortality.
Even granting the existence of an association between increasing body weight and higher mortality, at least for younger people, it does not follow that losing weight will reduce the risk. We simply do not know whether a person who loses 20 lb will thereby acquire the same reduced risk as a person who started out 20 lb lighter. The few studies of mortality among people who voluntarily lost weight produced inconsistent results; some even suggested that weight loss increased mortality.
All of this is not to say that being overweight (here defined as having a body-mass index over about 28) is not risky. Being substantially overweight -- that is, having a body-mass index of 30 or so -- is correlated with serious health problems, including coronary heart disease, hypertension, diabetes, and a variety of musculoskeletal problems. It has been shown that hyperglycemia, hyperlipidemia, and hypertension are ameliorated by a loss of as little as 10 to 15 percent of body weight. Thus, even though we do not know whether weight loss is beneficial in mildly or moderately obese people who are otherwise healthy, it does appear to have beneficial effects in patients with disorders such as hypertension and diabetes. Moreover, avoiding weight gain in the first place substantially reduces the likelihood that these conditions will develop.
Given the ambiguous benefits of weight loss, why are physicians and public health officials joining in the general enthusiasm for losing weight? Some influential public figures who were steeped in the struggle against tobacco use are describing obesity as a "disease," calling it the "second leading cause of preventable death" in the United States -- an arguable assertion. One reason may be that weight loss seems an easy way to reap better health outcomes in the population at large. In the year before fen-phen was removed from the market, approximately 18 million people took the drug combination -- prescribed by doctors. But as we have seen, losing weight and sustaining the loss are not nearly as easy as they sound; the benefits may be quite limited, and the risks of some methods may be large.
A second reason for the medical campaign against obesity may have to do with a tendency to medicalize behavior we do not approve of. In this age of political correctness, it seems that obese people can be criticized with impunity, because the critics are merely trying to help them. Some doctors take part in this blurring of prejudice and altruism by overstating the dangers of obesity and the redemptive powers of weight loss. On the other hand, some who object to society's prejudice against obesity engage in an overly rigid biologic determinism. They assert that obesity is no more within a person's control than eye color and thus has nothing to do with habits. Either way, the result is to see overweight people in medical terms, rather than as ordinary people who happen to be heavier than average, probably from some mixture of nature, nurture, and choice.
Why is it that people cannot seem to lose weight, despite the social pressures, the urging of their doctors, and the investment of staggering amounts of time, energy, and money? The old view that body weight is a function of only two variables -- the intake of calories and the expenditure of energy -- has given way to a much more complex formulation involving a fairly stable set point for a person's weight that is resistant over short periods to either gain or loss, but that may move with age. According to this concept, changes in feedback mechanisms under the control of the central nervous system alter both appetite and metabolism to defend the set point and prevent large fluctuations in weight. Of course, the set point can be overridden and large losses can be induced by severe calorie restriction in conjunction with vigorous, sustained exercise, but when these extreme measures are discontinued, body weight generally returns to its preexisting level. From studies of twins, it appears that hereditary factors play an important part in a person's weight and probably influence the slow change in the set point that occurs over a life span.
Undoubtedly, the best public health approach is to concentrate on measures to prevent obesity. A progressive fattening of the population is not inevitable. We need to do a better job of educating people about healthful diets, including the calorie content of common foods, without promoting fetishes. Encouraging lifelong, regular exercise in children may well have the greatest effect in terms of preventing obesity, as well as numerous other benefits. If the time children now spend in front of the television eating junk food and watching advertisements for more junk food was instead spent in physical activity, leanness would be virtually ensured. Healthful eating habits and regular exercise become even more critical in young adulthood, when a tendency toward obesity typically appears. Although we are still uncertain whether overweight is a direct cause of the illnesses associated with it and whether reductions in weight are beneficial, few would claim that becoming obese is consistent with optimal health.
Physicians can have their most important role in counseling patients about how to prevent obesity. But what should they tell patients who are already overweight? Because the causes of obesity are highly heterogeneous, doctors need to tailor their advice to each patient. Many overweight persons are happy and in reasonably good health, some overeat because they are depressed, and still others are depressed because they are overweight. In our view, doctors should provide advice if an overweight patient asks for help in planning a weight-loss program and recommend weight loss if a patient is suffering from health problems that can be ameliorated by weight loss, such as hypertension, diabetes, or osteoarthritis, or if a patient is so obese that he or she is clearly in jeopardy (for example, if the patient is virtually immobilized). In other situations, doctors should be cautious about exhorting patients to lose weight, especially when they are only mildly obese. Until we have better data about the risks of being overweight and the benefits and risks of trying to lose weight, we should remember that the cure for obesity may be worse than the condition.
Finally, doctors should do their part to help end discrimination against overweight people in schools and workplaces. We should also speak out against the public's excessive infatuation with being thin and the extreme, expensive, and potentially dangerous measures taken to attain that goal. Many Americans are sacrificing their appreciation of one of the great pleasures of life -- eating -- in an attempt to look like our semi-starved celebrities. Countless numbers of our daughters and increasingly many of our sons are suffering immeasurable torment in fruitless weight-loss schemes and scams, and some are losing their lives. Doctors can help the public regain a sense of proportion.
Jerome P. Kassirer, M.D.
Marcia Angell, M.D.
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