CARBOHYDRATE-TOLERANCE IMPROVES WITH FASTING IN OBESE SUBJECTS WITH NONINSULIN-DEPENDENT (TYPE-II) DIABETES

To determine the effects of shortterm fasting on carbohydrate tolerance, 10 obese women with noninsulin-dependent diabetes mellitus (NIDDM) were studied with meal tolerance tests before and after 3 days of fasting. After 3 days' fast, basal serum glucose declined from 15.2 ± 0.9 to 7.5 ± 0.7 mmol/L (273 ± 17 to 135 ± 13 mg/dL) (mean ± SEM, p < 0.001) and the glycemic response to the test meal (area under the glucose curve) improved by 31%. There were no changes in basal or postprandial insulin levels but a slight increase in serum c-peptide. Resting metabolic rate and the thermic effect of food were unchanged. There was a slight but insignificant change in basal and postprandial free fatty acid levels and a significant elevation of basal beta-hydroxybutyrate levels. Blood lactate rose significantly (from 0.9 to 2.0 mM) during the initial meal tolerance test, but no rise in lactate was seen in the meal tolerance test after fasting. Two subgroups of patients were identified based on the degree of glycemic improvement after shortterm fasting. Those with lesser improvement in serum glucose showed overnight rises in serum glucose during the period of fasting (the dawn phenomenon), while those patients who normalized serum glucose showed a steady fall in serum glucose. This finding may help to predict the glycemic response to long-term calorie restriction. Carbohydrate tolerance improves in obese diabetic (NIDDM) women after 3 days of fasting, in contrast to the impairment of glucose tolerance seen in lean or obese nondiabetic subjects after fasting. The improvement in carbohydrate tolerance is probably due to a combination of reduced hepatic glucose output and improved insulin action rather than enhanced sulin secretion.