NEGATIVE-ENERGY BALANCE WITH EXERCISE IN IDENTICAL-TWINS - PLASMA-GLUCOSE AND INSULIN RESPONSES

The effects of long-term (93 days) negative energy balance on plasma g lucose and insulin were investigated by means of exercise with constan t energy intake in seven pairs of young sedentary male identical twins . Results showed a significant decrease in fasting (-24%, P < 0.02) an d postprandial insulin (-16%, P < 0.05). Fasting and postprandial plas ma glucose and glucagon were not modified. Mean glucose disposal rate measured during a euglycemic-hyperinsulinemic clamp performed in five twin pairs was increased by 34% (P = 0.13). No significant intrapair s imilarity was found for the responses of fasting and postprandial insu lin levels and of glucose disposal rate. Changes in glucose disposal r ate were significantly greater in high compared with low losers for co mputerized tomography-measured abdominal visceral fat (3.0 +/- 1.1 vs. 0.3 +/- 0.5 mg . kg(-1) . min(-1), P < 0.05) despite similar losses i n total body fat. We conclude that 1) a long-term negative energy bala nce generated by exercise training significantly reduces plasma insuli n levels, whereas insulin sensitivity tends to be improved; 2) trainin g-induced changes in insulin sensitivity are associated with changes i n abdominal visceral fat; and 3) data from this experiment conducted w ith a small number of twin pairs suggest that the genotype does not se em to be a major determinant of the changes in insulin levels and sens itivity brought about by negative energy balance with exercise.