The response of protein and energy metabolism to food intake in lean and obese man.

Ten obese and five lean subjects were given continuous intravenous infusions of [1-14C]leucine for 24-h periods to measure rates of protein turnover in the whole body. Food was given as equal hourly meals during the first 12 h (day) and subjects were fasted for the remaining 12 h (night). In both lean and obese subjects rates of body protein synthesis and leucine oxidation were higher during the feeding phase, but body protein breakdown was higher during fasting. Simultaneous measurements of metabolic rate showed that overall the rates of protein synthesis were correlated with the oxygen consumption, but this correlation resulted mainly from differences due to feeding. Within a homogeneous group of obese women this correlation was not apparent when fed and fasted states were examined separately. The diurnal pattern of feeding and fasting was accompanied by storage and withdrawal from store of both protein and energy. There was no detectable difference in the pattern of storage between lean and obese subjects.