Weight-reducing diets, the thermic effect of feeding and energy balance in young women.

Six healthy women participated in a longitudinal study. In session one baseline data collection was made: (1) a record of customary food intake by the weighed inventory method; (2) the measurement of resting metabolic rate (RMR) and the thermic effect of feeding (TEF) a meal (2.09 MJ Ensure) together with the collection of blood samples; (3) the measurement of weight, height and assessment of body composition. On three subsequent occasions similar data were collected following periods of energy intake restriction, or free diet. Group mean (range) energy intake for session one (7 days) was 8.97 MJ (6.93-12.24); for session two (14 days) was 4.06 MJ (3.61-4.66); for session three (4 days) 1.75 MJ (1.15-2.20). No record was made for session four (free diet for 21 days). Subjects were 98-118 percent of ideal body weight at the study onset. All lost weight in sessions two and three, mean (range) 2.4 kg (1.0-3.7) and 1.4 kg (0.7-2.6) respectively. A mean of 2.2 kg (1.3-2.7) was gained in session four. Mean RMR was 122 kJ per 30 min in session one and fell by 12 percent of the mean baseline value in session two. Thereafter values returned to basal levels. TEF in session one increased mean (range) 30 percent (13-45) over RMR. There were no changes in session two. In session three TEF was 17 percent (10-28) and similar results were recorded in session four. The study suggests that TEF can be sensitive to alterations in energy intake and that this adaptive mechanism is highly variable among individuals. This has implications for the prediction of changes in body weight in response to varying levels of food intake.