Thermic effect of glucose and amino acids in man studied by direct and indirect calorimetry

1. In order to reinvestigate the classical concept of specific dynamic action of food, the thermic effect of ingested glucose (50 g) or essential amino acids (50 g) or both was measured in seven healthy male subjects dressed in shorts, by using both direct and indirect calorimetry simultaneously. Experiments were performed under conditions of thermal comfort at 28°.

2. Energy ‘balance’ (heat production minus heat losses) was negative during the control period (mean heat deficit: −16.0 ± 0.8 kJ/m²per h.

3. Metabolic rate increased 13.6 ± 1.8% after the glucose load, 17.2 ± 1.4% after amino acids, and 17.3 ± 2.9% after both glucose and amino acids: thus there was no additive thermic effect when both nutrients were given together.

4. In contrast to the metabolic rate, heat losses were not significantly altered after nutrient ingestion; consequently, the energy ‘balance’ became rapidly positive.

5. These results show that: (a) the food-induced thermogenesis, for a moderate energy intake, is less dependent on the nature of the nutrients than was classically admitted; (b) this increased heat production mainly induces changes in heat storage rather than in heat losses during the first hours following ingestion of a meal.