Reduced postprandial energy expenditure in women predisposed to type 2 diabetes

Type 2 (non-insulin dependent) diabetes is so common that it has been hypothesized that in the course of evolution the predisposition to it may have conferred some advantage, before or during the reproductive years. It is frequently preceded by gestational diabetes. In order to test the basis for the hypothetical advantage, energy expenditure was investigated in 10 women with documented transient diabetes in a previous pregnancy. They were studied early in a subsequent pregnancy while glucose tolerance wa still normal and 9 were re-studied after pregnancy. Their results were compared with normal matched controls. During pregnancy, resting energy expenditure was similar in the study group and controls (6.58 (5.77-7.55) median (range) vs 6.91 (6.56-7.36) MJ day-1, respectively). However, the energy response to a mixed meal (42 kJ, kg-1 lean body mass) was decreased in the study group (45 (33-68) vs 76 (50-89) kJ, p < 0.05). After pregnancy resting energy expenditure was again similar in the two groups, but the decrease in postprandial thermogenesis persisted (78 (59-84) vs 92 (79-105) kJ, p < 0.05). The patients were resistant to exogenous insulin, 0.05 U kg-1 intravenously (slope of the plasma glucose decline in the 15 min after insulin; during pregnancy patients 52 (37-92) vs controls 111 (104-121) mumol l-1 min-1, p < 0.01; after pregnancy 130 (88-156) vs controls 186 (152-221) mumol l-1 min-1, p < 0.01). The postprandial energy saving in these women could constitute an evolutionary advantage. Insulin resistance may be the mechanism for limiting postprandial thermogenesis.