Thermic effect of a meal. 2. Role in chronic undernutrition.

The thermic effect of a standard liquid meal (TEM; energy 2.5 MJ; containing (g/kg) protein 100, fat 150, carbohydrate 750; volume 350 ml) was measured in a chronically undernourished (UN; n 9) group of human subjects and was compared with results from two control groups, one normal weight (NW)-for-height (BMI greater than 20; n 10) and the other underweight (UW)-for-height (BMI less than 18, n 10), using a ventilated-hood system over a period of 6 h after ingestion of the meal. Results indicated that the UN subjects had lower values for body-weight, height, percentage fat and fat-free mass (FFM) compared with those of either control group. Basal metabolic rates were lowest in the UN group in absolute terms; however, there were no significant differences among groups on an analysis of covariance (ANACOVA) with FFM as the covariate. TEM responses in the UN group were significantly higher when expressed either in absolute terms or as a percentage of the energy density of the meal. The post-meal total energy output was significantly lower (P less than 0.05) in the UW and UN groups as compared with the NW group in absolute terms; however, on adjusting for differences in FFM (by ANACOVA) there were no significant differences among groups. This would suggest that in the chronically undernourished thermogenic responses to a meal are unlikely to contribute towards any energy saving and may not constitute a part of any adaptive response to the undernourished state.