Evidence for reduced thermic effect of insulin and glucose infusions in Pima Indians

Several authors have reported a reduced thermic effect of food in obese subjects. The hyperinsulinemic-euglycemic clamp technique has been used to measure one component of the thermic effect of food, insulin and insulin-mediated glucose disposal. We used this technique to measure the thermic responses to insulin and glucose infusions in 120 glucose-tolerant Pima Indians, a population with a high prevalence of obesity. During high-dose insulin infusions (400 mU/m2 per min) the measured increase in energy expenditure (MEE), 150 +/- 6 cal/min, was greater than the predicted increase in energy expenditure (PEE), 72 +/- 2 cal/min, for glucose storage as glycogen. During low-dose insulin infusions (40 mU/m2 per min) the mean MEE, 6 +/- 5 cal/min, was not significantly different from zero and was not greater than the mean PEE, 9 +/- 1 cal/min. These data were in contrast to results obtained from Caucasians by others and suggested a markedly reduced thermic effect of low-dose insulin and glucose infusions in Pima Indians. We also studied 23 glucose-tolerant male Caucasians and compared their results with the results from male Indians matched for glucose storage rates and obesity. The results showed that the thermic response to insulin and glucose infusions was similar in the two racial groups during high-dose insulin infusions but was markedly reduced in the Indians compared with the Caucasians during low-dose insulin infusions.