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 II 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.