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Three major factors modulate body weight: metabolic factors, diet, and physical activity, each influenced by genetic traits. Despite recent advances in these areas, the prevalence of obesity in Westernized societies has increased. In contrast to monogenic animal models and rare human genetic syndromes, predisposition to common forms of obesity is probably influenced by numerous susceptibility genes, accounting for variations in energy requirements, fuel utilization, muscle metabolic characteristics, and taste preferences. Although recent increases in obesity prevalence cannot be explained by changes in the gene pool, previously 'silent' genetic variants may now play important permissive roles in modern societies. Available data suggest that variations in resting energy expenditure, thermic effect of food, and fuel utilization exist but, by themselves, are unlikely to explain the onset of obesity. Regarding diet, the best available trend survey data indicate that fat and energy intake have fallen, in this and other Westernized countries. Diverging trends of decreasing energy intake and increasing body weight suggest that reduced physical activity may be the most important current factor explaining the rising prevalence of obesity. Subsistence in modern societies requires extreme adaptations in previously useful energy-conserving diet and exercise behaviors. Recognizing the difficulties in sustaining energy-restricted diets in the presence of fast foods and social feasts, the current trend toward increasing body weight is not likely to be reversed solely through recommendations for further reductions in energy intake. In all likelihood, activity levels will have to increase in response to an environment engineered to be more physically demanding. Am J Med. 1998;105:145-150. [C] 1998 by Excerpta Medica, Inc.

PURPOSE: To compare recent changes in diet and physical activity with trends in body weight and obesity prevalence, using large survey studies representative of the US population. MATERIALS AND METHODS: Secular-trends survey studies were made from databases of NHANES 11 and III, USDA Nationwide Food Consumption Survey, Behavioral Risk Factor Survey System, and Calorie Control Council Report providing data on obesity prevalence, body mass index, calorie and fat intake, exercise-related physical activity, and consumption of low-calorie food extracted from surveys for the adult US population and specific subgroups. RESULTS: In the adult US population the prevalence of overweight rose from 25.4% from 1976 to 1980 to 33.3% from 1988 to 1991, a 31% increase. During the same period, average fat intake, adjusted for total calories, dropped from 41.0% to 36.6%, an 11% decrease. Average total daily calorie intake also tended to decrease, from 1,854 kcal to 1,785 kcal (-4%). Men and women had similar trends. Concurrently, there was a dramatic rise in the percentage of the US population consuming low-calorie products, from 19% of the population in 1978 to 76% in 1991. From 1986 to 1991 the prevalence of sedentary lifestyle represented almost 60% of the US population, with no change over time. CONCLUSIONS: Reduced fat and calorie intake and frequent use of low-calorie food products have been associated with a paradoxical increase in the prevalence of obesity. These diverging trends suggest that there has been a dramatic decrease in total physical activity related energy expenditure. Efforts to increase the average American's total exercise- and nonexercise-related physical activities may be essential for the prevention of obesity. Am J Med. 1997;102:259-264. [C] 1997 by Excerpta Medica, Inc.

PURPOSE: Although weight reduction generally lowers blood pressure, it is unclear whether the resPOnse is due to concurrent dietary changes or to reduced body mass itself. in this study, the independent effects of energy restriction and weight reduction were examined prospectively in 24 obese, hypertensive, normoglycemic women whose dietary intake was tightly controlled. SUBJECTS AND METHODS: Sodium, potassium, and calcium intake, the polyunsaturated/saturated fat ratio, and the proportional composition of carbohydrate, fat, and protein were constant throughout the 5-month protocol. Hemodynamic and neuroendocrine status was evaluated in four 10-day hospital phases.- two prior to weight loss (energy balance and then 800-kcal intake), and two after an average loss of 13 kg to normal body weight (800 kcal and then return to energy balance). RESULTS: Fasting serum insulin, trilodothyronine inreverse trilodothyronine ratio, resting metabolic rate, and heart rate declined, and sodium and potassium balances were negative during energy restriction. Catecholamines, renin, aldosterone, plasma volume, cardiac output, and blood pressure showed no consistent response to changes in energy intake. By contrast, weight reduction independently lowered blood pressure, plasma volume, cardiac output, and plasma renin activity. Body fat pattern remained unchanged. CONCLUSION: These results demonstrate that weight loss has a blood pressure-lowering effect that is distinct from energy restriction and that is related to changes in blood volume and cardiac output., Evidence exists that people who are overweight are more prone to high blood pressure. When patients are placed on restricted diets to lose weight, blood pressure also decreases. Three factors involved in dieting may account for these decreases: lower caloric intake, reduced sodium intake, and decreased body fat content. No study has conclusively shown that any of the decrease in blood pressure is attributable to the decreased body fat alone rather than to the caloric and sodium restrictions. This study examined the separate effects of caloric restriction and decreased body fat on lowering blood pressure. The study followed 24 women who were mildly obese and had mild to moderate hypertension (high blood pressure). The women were placed on a restricted-calorie diet to decrease body fat, but were given constant levels of sodium and other nutrients, as well as carefully proportioned diets, to eliminate other factors from contributing to decreased blood pressures. Once the women had reached a nearly normal weight, caloric content was increased to a maintenance level to factor out caloric restriction in blood pressure results. The subjects lost an average of 17 percent of their body weight during the study. Blood pressures in the subjects were significantly lower at the end of the study than at its beginning. Analysis of blood pressure data taken throughout the study revealed that decreases in blood pressure were statistically related to decreased body fat, but not to caloric restriction. Metabolic measurements of insulin and other substances followed the pattern expected for caloric restriction, but did not closely correlate with blood pressure. Thus, blood pressure decreases seen in subjects who restrict calories are not only a short-term effect of caloric deprivation, but also an effect of body fat reduction. (Consumer Summary produced by Reliance Medical Information, Inc.)

OBJECTIVE: Currently recommended rates of weight loss for obese persons are not based on demonstrated health risks. The authors attempt to determine a medically safe rate of weight loss based on currently available data on the risk of gallstone formation during active weight loss. METHODS: All prospective studies published in the English language on the formation of gallstones in obese persons during active weight loss were reviewed and evaluated. A statistical analysis was performed using studies of at least 4 weeks' duration that included information on diet composition, rates of weight loss, length of follow-up, and incidence of gallstone formation. A statistical model was fit to the data from the studies that met the criteria. RESULTS: Nine subject groups derived from five published reports met the criteria for inclusion in the analysis. When the results of these groups were evaluated statistically, a curvilinear relationship between incidence of gallstone formation and rate of weight loss was demonstrated. The relationship was best described by an exponential regression curve, with an adjusted [r.sup.2] of 0.98 and a dramatically increasing risk of gallstone formation at rates of weight loss above 1.5 kg per week. CONCLUSION: Risk of gallstone formation in obese persons during active weight loss seems to increase in an exponential fashion. The data suggest that rates of weight loss should not exceed an average of 1.5 kg per week.