ATHLETES WITH IDDM EXHIBIT IMPAIRED METABOLIC CONTROL AND INCREASED LIPID UTILIZATION WITH NO INCREASE IN INSULIN SENSITIVITY

Physical exercise is traditionally recommended to diabetic patients as part of their treatment. Although healthy athletes exhibit enhanced s keletal muscle insulin sensitivity, the metabolic effects of vigorous training in patients with insulin-dependent diabetes mellitus (IDDM) a re not known. This study was designed to examine the effects of compet itive sports on fuel homeostasis and insulin sensitivity in athletes w ith IDDM. We studied 11 athletes and 12 matched sedentary men with IDD M. In each subject, we measured glycemic control, insulin-stimulated g lucose uptake in the whole body and forearm, rates of glucose and lipi d oxidation, and muscle glycogen, glycogen synthase, and glucose trans port protein (GLUT4) concentrations. The athletes had higher VO2max (5 2 +/- 1 vs. 42 +/- 1 ml . kg(-1) . min(-1), P < 0.001) and HbA(1c) lev els (8.4 +/- 0.4 vs. 7.2 +/- 0.2%, P < 0.05) than sedentary patients, but took smaller insulin doses (41 +/- 3 vs. 53 +/- 3 U/day, P < 0.05) . The insulin-stimulated rates of whole-body and forearm glucose uptak e and glucose oxidation were similar in the two groups, whereas both e nergy expenditure and lipid oxidation were increased in the athletes, Lipid oxidation correlated inversely with glycogen synthase activity. The mean glucose arterialized venous blood-deep venous blood (A-V) dif ference during the insulin infusion (60-240 min) correlated with the w hole-body glucose disposal throughout the insulin infusion (after 60 m in, r > 0.73, P < 0.001 for all 30-min periods). This association is a ccounted for by the relationship between glucose A-V difference and no noxidative glucose disposal. Muscle glycogen and GLUT4 protein content s were not different in the two groups. In conclusion, in athletes wit h IDDM: 1) competitive exercise performed at variable schedules and in tensities leads to a decrease in required insulin dose, impairment of metabolic control, and increase in lipid utilization; 2) insulin sensi tivity is not enhanced; and 3) glucose A-V difference, not blood flow, is the major determinant of body sensitivity to insulin. Thus, more i ntense glucose monitoring and education may be required for the mainte nance of good control in patients with IDDM involved in competitive sp orts.