Prior meal enhances the plasma glucose lowering effect of exercise in type 2 diabetes.

PURPOSE: To compare the changes in plasma glucose and insulin levels in response to 1 h of exercise performed at 60% of VO(2peak) either in the fasted state or 2 h after a standardized breakfast in subjects with type 2 diabetes. METHODS: Ten sedentary men with type 2 diabetes treated with oral agents and not under strict metabolic control were tested on two occasions (fasted and fed state) in a random order at a 1-wk interval. RESULTS: Plasma glucose was slightly but not significantly higher at the beginning of exercise performed in the fed state versus the fasted state (12.4 +/- 1.3 vs 11.1 +/- 1.1 mmol x L(-1) respectively; mean +/- SE, P = 0.06). However, after exercise, plasma glucose levels were much lower in the fed state (7.6 +/- 1.1 mmol x L(-1)) compared with the fasted state (10.0 +/- 1.0 mmol x L(-1); P = 0.009). Insulin levels were higher at the beginning of the exercise bout performed in the fed state (177 +/- 26 vs 108 +/- 19 pmol x L(-1); P < 0.05) and during exercise. Similar respiratory exchange ratio at identical workload indicated that the difference in glycemic response was not due to differences in whole body substrate utilization. Plasma concentrations of free fatty acids, glucagon, epinephrine, and norepinephrine were also similar during both experiments. CONCLUSIONS: One hour of aerobic exercise has a minimal impact on plasma glucose level when performed in fasted moderately hyperglycemic men with type 2 diabetes but induces an important decrease in plasma glucose level when performed 2 h after breakfast. Because glucose utilization increased similarly during exercise in both conditions, the higher insulin levels after the meal might have blunted glucose production, creating an imbalance between total glucose production and total peripheral utilization in the fed state in contrast to the fasted state.

Impact of time interval from the last meal on glucose response to exercise in subjects with type 2 diabetes.

We evaluate the influence of the time interval from the last meal on the blood glucose response to exercise in men with type 2 diabetes. Nineteen men with type 2 diabetes participated in an exercise training program carried out at 60% of maximal oxygen uptake (VO2peak) for 1 h, 3 times a week. Capillary whole blood glucose was measured immediately before and after each exercise session, and the time interval from the last meal (breakfast, lunch, or dinner) was recorded. Seven time intervals were considered (fasted overnight and 0-1, 1-2, 2-3, 3-4, 4-5, and 5-8 h postmeal). A total of 1,045 exercise sessions were analyzed. There was no change in blood glucose levels when individuals were in the fasted state (mean +/- SE, 8.1 +/- 0.2 vs. 8.1 +/- 0.1 mmol/L; before vs. after, respectively). However, blood glucose decreased by 28 +/- 1% at 0-1 h, by 33 +/- 1% at 1-2 h, by 35 +/- 1% at 2-3 h, by 38 +/- 2% at 3-4 h, by 43 +/- 2% at 4-5 h, and by 23 +/- 3% at 5-8 h (all P < 0.001). These results demonstrate that 1 h of ergocycle exercise has no clinical impact on blood glucose when performed in the fasted state in men with type 2 diabetes, whereas a significant decrease in blood glucose should be expected when the same exercise is performed postprandially.

Role of body fat loss in the exercise-induced improvement of the plasma lipid profile in non-insulin-dependent diabetes mellitus.

The study was designed to examine the impact of exercise training on the plasma lipid profile in non-insulin-dependent diabetes mellitus (NIDDM) and, more particularly, to determine the relationship between changes in body fat mass and changes in the lipid profile. Eleven men with NIDDM exercised for 1 hour thrice per week on an ergocycle over a 6-month period at 60% maximal oxygen uptake (Vo2max). Diet and hypoglycemic agents were kept constant throughout this period. Vo2max, body composition, fasting plasma glucose and insulin levels, glycosylated hemoglobin, and the lipid profile were determined at baseline, in the middle (3 months), and at the end (6 months) of the training program. When the subjects were considered as a group, the only significant effect of training was on Vo2max, which increased from 32.2 +/- 1.2 mL/kg/min at baseline to 38.0 +/- 1.7 mL/kg/min at 6 months (P < .001). When the data were analyzed on an individual basis, significant associations were observed between changes in body fat mass and changes in the low-density lipoprotein (LDL) cholesterol/high-density lipoprotein (HDL) cholesterol ratio (r = .62,P = .04) or triglyceride (TG) levels (r = .64,P = .03). These data indicate that fat loss, not training per se, favorably alters the lipid profile of subjects with NIDDM who participate in an aerobic physical-conditioning program.

Counterregulatory response to insulin-induced hypoglycemia in trained and nontrained humans.

The aim of the present series of experiments was to investigate the hormonal counterregulatory response to insulin-induced hypoglycemia in trained and nontrained healthy individuals. Five endurance athletes and six controls were administered intravenous insulin infusion at a rate of 0.15 U/kg/h until plasma glucose reached 50 mg/dL. The mean duration of the infusion in the trained and nontrained subjects corresponded to 18.6 and 26.3 minutes (P less than .01), suggesting that the former were characterized by an increased insulin sensitivity. Plasma glucose levels were similar in the two groups at the end of the insulin infusion, as well as during the postinfusion recovery period. Forty-five minutes after the end of the infusion, plasma glucose levels were not significantly different from the preinfusion levels in the two groups. During this period of glycemia recovery, the increases in plasma glucagon, epinephrine, norepinephrine, and growth hormone were at least 50% lower in the trained than in the nontrained subjects. The increase in heart rate and oxygen uptake during the same period of time was significantly higher in the trained subjects. To determine whether this reduced hormonal response to hypoglycemia was due to reduced insulin levels or to an increased sensitivity to counterregulatory hormones, we investigated the effect of epinephrine on plasma glucose in two other groups of trained and nontrained subjects. In response to a constant epinephrine infusion of 0.01 or 0.1 micrograms/kg fat-free mass (FFM)/min, plasma glucose levels increased similarly in the two groups. In conclusion, these results indicate that trained subjects are characterized by a normal recovery from hypoglycemia despite a reduced response of counterregulatory factors.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered plasma free carnitine response to exercise in type 1 diabetic subjects.

The plasma carnitine response to prolonged exercise in 12 postprandial insulin-dependent diabetics was compared with that of eight normal controls. The diabetics reduced their morning dose of intermediate acting insulin and regular insulin to two-thirds and one-half, respectively. Insulin was injected subcutaneously into the abdominal wall. Exercise was performed on a treadmill for 90 min at 60% VO2 max. Respiratory exchange ratios (RER) decreased significantly (p less than 0.0001) during exercise in both the control and diabetic group. However, RER values were higher (p less than 0.05) in the diabetic group during most of the exercise period, corresponding to a significantly (p less than 0.05) lower proportion of the energy utilized from the oxidation of fat. In the diabetic group, mean plasma glucose at rest was 278 +/- 26 mg/dl, and decreased significantly (p less than 0.01) to 107 +/- 12 mg/dl after 90 min of exercise. In the control group, mean resting plasma glucose was 78 +/- 6 mg/dl, and dropped (p less than 0.05) to 67 +/- 3 mg/dl at 30 min of exercise. Thereafter, it showed no change. Mean resting plasma free insulin in the control group was lower compared to the diabetic group (10.2 +/- 2.0 vs 23.5 +/- 2.0 microU/ml, p less than 0.001). During exercise, insulin levels decreased significantly (p less than 0.01) in the control group while there was no change in the diabetic group. In both control and diabetic groups, percent basal total carnitine increased significantly (p less than 0.01) throughout exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of exogenous insulin on plasma free carnitine levels during exercise in normal man.

Preliminary data from our laboratory have shown that the decrease in plasma free carnitine levels normally found during prolonged exercise is blunted in type 1 diabetic man. This study was designed to test the hypothesis that this might be due to the sustained peripheral hyperinsulinemia seen during exercise in diabetics treated by subcutaneous insulin. Ten male subjects underwent 90 min of cycle ergometry at 60% of their maximal oxygen uptake capacity on two occasions, one with and the other without a constant 0.13 mU.kg-1.min-1 i.v. insulin infusion. Blood samples were taken at rest, during exercise, and after exercise for measurement of plasma glucose, insulin, C-peptide, free fatty acids, and carnitine. Plasma glucose dropped significantly (p less than 0.01) from basal during both infusions, but values at 30, 45, and 60 min of exercise were lower (p less than 0.05) during insulin infusion compared with the saline infusion. Exercise produced a significant (p less than 0.01) fall in plasma insulin in both infusions. However, from 30 to 90 min of exercise, the plateau insulin level was higher during the insulin infusion compared with the saline infusion (91.4 +/- 3.0 vs. 32.9 +/- 3.0 pmol/L; p less than 0.001). Plasma C-peptide decreased significantly (p less than 0.01) during exercise and recovery in both infusions, but values between infusions were not significantly different. Plasma free fatty acids increased significantly (p less than 0.01) at 90 min of exercise during the saline infusion, while during the insulin infusion this was noted during recovery only.(ABSTRACT TRUNCATED AT 250 WORDS)