The thermic effect of food in normal-weight and overweight pregnant women

Abstract

A defective thermic response to food may be an energy-sparing adaptation in both obesity and pregnancy. To evaluate the combined effect of obesity and pregnancy on postprandial thermogenesis, the thermic effect of food was assessed for a 240 min period following a high-carbohydrate meal and a typical mixed meal in nine normal-weight non-pregnant, eight overweight non-pregnant, eight normal-weight pregnant and six overweight pregnant women using indirect calorimetry. A test meal that provided 60% of each subject's measured daily requirement for basal metabolism was used. Pregnant women were studied during weeks 30–35 of gestation. Neither obesity nor pregnancy altered the thermic effect of food, although the response to the mixed meal was greater ( P <0·01) than that to the high-carbohydrate meal in all cases. The mean responses for the high-carbohydrate and mixed meals were 26·9 (SD 6·0) and 30·1 (SD 6·2)% baseline energy expenditure respectively, and 7·4 (SD 1·6) and 8·3 (SD 1·6)% of the meal energy load respectively. Obesity and pregnancy were associated with hyperinsulinaemia ( P <0·005) following both test meals, suggesting that postprandial thermogenesis was not altered by insulin resistance in this group. The incremental glucose response was elevated ( P <0·001) in the pregnant women following both test meals; overweight women tended to have a greater incremental glucose response following the high-carbohydrate meal, but it was not significant ( P = 0·065). These results do not provide evidence of an impaired thermic response to food in either overweight or third trimester pregnant women.