Summary of the National Obesity and Weight Control Symposium: Columbia-Presbyterian Medical Center, April 1993
Theodore B. Vanitallie
This conference dealt in part with issues raised by the inclusion in the 1990 Dietary Guidelines for Americans of a new unisex standard for body weight, which encouraged heavier weight for adults over 35 years of age. Since currently the public health emphasis in regard to appropriate body weights is clearly on weight control and the prevention of obesity, the endorsement of this standard by a committee of the U.S. Department of Agriculture and the Department of Health and Human Services poses a dilemma. Whereas the data for the 1985 ‘Desirable Body Weight Ranges” is based on the Metropolitan Relative Weights validated by mortality and morbidity in the long-term follow-up of the Framingham Heart Study, the data base for the 1990 Suggested Weights for Adults” is obscure.
To aid readers in appreciating the impact of the change in standards, we reproduce here the differing standards endorsed in the 1985 (based on the 1959 Metropolitan Desirable Weight Table) and in the 1990 Dietary Guidelines for Americans. For previous discussions of the rationale for establishing standards of desirable body weight, readers are referred to Willett et al. (New guidelines for Americans: Justified or injudicious? Am J Clin Nutr1991;53:1102-3) and Simopoulos and VanItallie (Body weight, health and longevity. Ann Intern Med 1984;100:285-95).
This symposium was sponsored by various components of the Columbia-Presbyterian Medical Center, including its American Institute of Life-Threatening Illness and Loss, the Institute for Health and Weight Sciences-Center for Healthful Living (New York), The Center for Genetics, Nutrition and Health (Washington, DC), the Duke University Diet and Fitness Center and the Comprehensive Weight Control Center at New York Hospital-Cornell University Medical Center. During the 3-day meeting, scientists representing institutions throughout the United States presented the results, and their analyses of the implications, of recent research concerned with the great variety of effects of obesity on health and longevity, the causes of obesity and its various treatments.
The meeting opened with a consideration of the evolutionary aspects of diet and the persistent impact of the adaptations developed by humans during their early existence as hunters and food gatherers on their ability to cope with an industrialized society characterized by an abundant and palatable food supply and a sedentary life-style. It was pointed out that human beings appear to have evolved on a diet low in saturated fats and balanced in amounts of [omega]-6 a [omega]-3 fatty acids from seeds, green leafy vegetables, fish and meat from wild animals and birds. Furthermore, trans-fatty acids occur rarely in nature whereas they contribute about 7% of calories in today’s U.S. food supply. Viewed in this perspective, it is not surprising that people who five in industrialized societies are at high risk of becoming obese and of developing nutrition-related killer diseases such as coronary heart disease, certain cancers, stroke and diabetes mellitus.
Considering the high prevalence of obesity in the United States with its associated toll in excess morbidity and mortality, great concern was expressed over the relaxation of weight standards for Americans implicit in the 1990 Nutrition Guidelines developed jointly by the U.S. Department of Agriculture and the Department of Health and Human Services. It was pointed out that the results of many epidemiologic investigations, including recent data from a 38-year follow-up of the Framingham Heart Study and from the Nurses’ Health Study, indicate clearly that even a small increase in adiposity over that associated with an optimal weight range (a body mass index [BMI] of 21 to 25 kg/[m.sup.2]) is associated with a significantly increased risk of developing coronary heart disease, hypertension, noninsulin-dependent diabetes mellitus and other obesity-associated diseases. The longer obesity persists the greater the risk; moreover, weight gain during adult life adds to the risk of developing such health problems as coronary heart disease and diabetes. Accordingly, the conferees found it difficult to understand why the U.S. Dietary Guidelines provide for a liberalization of weight standards as people age.
As regards the causes of obesity, recent studies from a number of research centers have shown that an appreciable part of human obesity, perhaps as much as 79%, has a genetic component. However, the contribution of genetic endowment to man’s predisposition to become obese is complex and appears to have a number of phenotypic expressions. Also, the ability of a genetically predisposed individual to develop obesity depends on the exposure of that individual to a suitable obesity-promoting environment. Thus, the development of obesity represents a complex interaction between the susceptible individual and an environment that fosters obesity.
Among the possible causes of obesity that were discussed, sedentary life-style and a diet high in fat content were ranked high. Over time, fat may not be as satiating as the other macronutrients. Moreover, compared to dietary carbohydrate, dietary fat is converted more efficiently to depot fat. Indeed, it is easier to fatten humans and laboratory animals on a high-fat than on a high-carbohydrate diet. As the content of saturated fatty acids and trans-fatty acids increases in the diet, there occurs a corresponding decrease in the C20-22 polyunsaturated fatty acids in muscle membranes, which can lead to hyperinsulinemia prior to onset of obesity – a situation aggravated by increasing obesity.
Among the many inherited characteristics that could predispose an individual to excessive weight gain are:
* a relatively low physical activity level;
an imbalance of autonomic tone with sympathetic nervous
* a relative increase in insulin sensitivity predating and
possibly heralding an increase in weight gain;
* a relative impairment of ability to utilize one’s own fat
stores (manifested by a higher than normal respiratory
quotient [RQ] in the postabsorptive state);
* a reduced resting metabolic rate;
* a reduced thermic response to food ingestion;
* abnormal arachidonic acid metabolism; and
* various hormonal imbalances, such as overproduction of cortisol.
As regards the treatment of obesity, it was pointed out that while, in theory, behavior therapy should be very effective in the long-term management of obesity, in practice, it has been disappointing as a therapeutic modality. Despite the extensive use of behavior therapy during the weight loss and weight maintenance phases of obesity treatment, a large proportion of formerly obese patients (up to 95%) have regained all or most of weight lost in 2 to 5 years. Because of frustration over the relative ineffectiveness of conventional behavior therapy, a modified version of behavior therapy has been proposed based on the proposition that weight control is a learned life management skill. Thus, the goal of the new model is to break the recurring patterns of behavior and cognition associated with losses of control over food and weight gain.
It was emphasized that in the treatment of obesity by various low-calorie regimens, all too many therapists and weight-control programs neglect accumulated scientific knowledge about the physiologic responses of obese patients to stringent calorie restriction. Hence, calorie prescriptions designed to induce weight loss often fail to take into account the fact that the energy requirement for weight maintenance can vary widely in overweight patients and hence, their responses to a diet that is fixed in energy content vary also. Moreover, it is not unusual for treatment programs to permit patients to reduce weight too rapidly – that is, at rates at which the fat-free mass constitutes an undesirably high proportion of the weight loss. If continued for many weeks, such “poor quality” weight loss is associated with an increased incidence of avoidable side effects which, in extreme cases, can include the development of sudden ventricular arrhythmias.
Recent developments in the pharmacologic management of obesity were discussed, with particular emphasis placed on the potential usefulness of the newer serotonin agonists. It was noted that agents that are nonaddicting and relatively free from untoward side effects may prove to be useful in assisting patients to maintain reduced weight after therapeutic weight loss. The proposition that long-term treatment with an antiobesity medication can help patients avoid weight regain while they are participating in a professionally supervised maintenance program urgently needs testing.
Obesity is becoming increasingly common among children and adolescents and, at present, about 26% of adult Americans ages 20 to 74 years are overweight. In view of the alarmingly high prevalence of obesity in the United States and the fact that so many illnesses are caused or made worse by this condition, many of the conferees expressed dismay that American medical schools offer so little teaching about obesity and weight control. It was agreed that a reexamination of this situation is an urgent priority. A future conference to address this problem is planned for 1994 under the same sponsorship.
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COPYRIGHT 1993 Lippincott/Williams & Wilkins
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