Occasional physical inactivity combined with a high-fat diet may be important in the development and maintenance of obesity in human subjects

Background: A better understanding of the environmental factors that contri bute to obesity is imperative if any therapeutic effect on the increasing p revalence of overweight and obesity in the United States is to be achieved. Objective: This study examined the effect of the interaction of diet compos ition and physical inactivity on energy and fat balances. Design: Thirty-five normal-weight and obese subjects were randomly assigned to either a 15-d isoenergetic high-carbohydrate (HC) or high-fat (HF) diet according to a crossover design. During the first 14 d, body weight and ph ysical activity were maintained. On day 15, subjects spent 23 h in a whole- room indirect calorimeter and were fed a diet similar to that consumed duri ng the previous 7 d while remaining physically inactive. Results: Energy intakes required to maintain body weight stability during t he first 14 d were similar between diets. Normal-weight and obese subjects consuming both diets had a positive energy balance on the sedentary day (da y 15), suggesting that subjects were less active in the calorimeter. There was no significant effect of diet composition on total energy balance and t otal protein-energy balance on day 15; however, carbohydrate balance was mo re positive with the HC (2497.8 +/- 301.2 kJ) than with the HF (1159 +/- 30 1.2 kJ) diet (P = 0.0032). Most importantly, fat balance was more positive with the HF (1790.8 +/- 510.4 kJ) than with the HC (-62.8 +/- 510.4 kJ) die t (P = 0.0011). Conclusion: Chronic consumption of a high-carbohydrate diet could provide s ome protection against body fat accumulation in persons with a pattern of p hysical activity that includes frequent sedentary days.