Decreased thermic effect of a mixed meal during overnutrition in human obesity.

Short-term mixed calorie overfeeding increases basal energy expenditure in man but its effects on the thermic effect of a meal (TEM) are unclear. The thermogenic and hormonal responses to an 800-kcal liquid mixed meal were measured in six lean and six obese subjects during weight maintenance, during 18 d of overfeeding 1000 kcal/d, and during 18 d of a 589 kcal/d diet (obese subjects only). There was no change in the TEM in lean subjects between weight maintenance and overfeeding. In the obese group the TEM was lower during both overfeeding (p less than 0.05) and underfeeding (p less than 0.05) compared with weight maintenance. Overfeeding increased rates of net postprandial glucose oxidation and decreased lipid oxidation in the lean subjects only. Alterations in glucose oxidation rates and the insulin response to meals may contribute to an impaired TEM in human obesity during overnutrition.