The Effect of Exercise with or Without Metformin on Glucose Profiles in Type 2 Diabetes: A Pilot Study

The study's goals were 1) to confirm the previously observed increase in postprandial glucose levels immediately after exercise in people with type 2 diabetes who are being treated with metformin; 2) to determine how long the increased glucose persists; 3) to examine the effect of skipping a dose of metformin before or after exercise. We recruited 10 participants with type 2 diabetes who were taking metformin. They completed 4 experimental conditions in random order: 1) morning and evening metformin doses, without exercise (M-M); 2) morning and evening metformin doses, with exercise (M-Ex-M); 3) exercise with evening metformin dose only (Ex-M); and 4) morning metformin dose only, with exercise (M-Ex). Exercise consisted of walking for 50 minutes at a moderate intensity at 11 am on the first day of each condition. Glucose was measured for 72 hours using continuous glucose monitoring systems. Standardized breakfasts were provided for 3 days in each condition, and standardized lunches and dinners were provided on the first day. Compared to M-M, M-Ex-M increased the average 2-hour incremental postprandial area under the curve following the 5 standardized meals (p<0.01) but did not affect daily mean glucose or fasting glucose concentrations. M-Ex (p<0.05), but not Ex-M (p=0.08) increased mean glucose concentrations compared to M-Ex-M on day 1. There were no differences among the 3 exercise conditions for fasting or postprandial glucose concentrations. The addition of a bout of exercise to metformin led to an increase in postprandial glucose levels without affecting mean glucose concentrations. Removing a metformin dose before or after exercise did not attenuate this negative effect.