Although exercise is a central therapeutic modality in insulin-dependent diabetic patients, its prescription and expected effects have remained far less precise than the concurrent modalities of insulin and diet. To quantify the potential benefit of exercise on meal glycemic excursions, eight insulin-dependent diabetic subjects were studied on two separate days during breakfast and lunch, with and without 45 min of moderate exercise, starting 30 min after breakfast. All other variables were kept constant, including their usual insulin doses, which were given subcutaneously in the abdomen. Fasting glycemias were brought to comparable levels by overnight insulin infusion (rest day: 110 ± 9 mg/dl; exercise day: 105 ± 9 mg/dl). Postprandial exercise reduced peak glycemia for breakfast (270 ± 22 versus 203 ± 22 mg/dl) and lunch (270 ± 16 versus 170 ± 20 mg/dl, P < 0.05) for the group as a whole on rest day and exercise day, respectively. Three types of individual responses were seen. Five subjects showed an improved glycemic excursion with exercise during both breakfast and lunch. In two subjects only the lunch response was significantly improved. One subject showed no effect of exercise. The failure to demonstrate a lowering of glycemia with breakfast appears to be related to the persistent use of fatderived fuels in these subjects. This is suggested by a lower respiratory quotient (RQ), and elevated free fatty acid and 3-hydroxybutyrate concentrations. Plasma “free” insulin and glucagon concentrations could not account for these observations. Thus, the majority of subjects showed improved glucoregulation related to exercise performed postprandially. If adequately insulinized, conventionally treated diabetic individuals can benefit from strategically timed exercise.

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