A higher-carbohydrate, lower-fat diet reduces fasting glucose concentration and improves β-cell function in individuals with impaired fasting glucose

Abstract

The objective was to examine the effects of diet macronutrient composition on insulin sensitivity, fasting glucose, and β-cell response to glucose. Participants were 42 normal glucose-tolerant (NGT; fasting glucose <100 mg/dL) and 27 impaired fasting glucose (IFG), healthy, overweight/obese (body mass index, 32.5 ± 4.2 kg/m(2)) men and women. For 8 weeks, participants were provided with eucaloric diets, either higher carbohydrate/lower fat (55% carbohydrate, 18% protein, 27% fat) or lower carbohydrate/higher fat (43:18:39). Insulin sensitivity and β-cell response to glucose (basal, dynamic [PhiD], and static) were calculated by mathematical modeling using glucose, insulin, and C-peptide data obtained during a liquid meal tolerance test. After 8 weeks, NGT on the higher-carbohydrate/lower-fat diet had higher insulin sensitivity than NGT on the lower-carbohydrate/higher fat diet; this pattern was not observed among IFG. After 8 weeks, IFG on the higher-carbohydrate/lower-fat diet had lower fasting glucose and higher PhiD than IFG on the lower-carbohydrate/higher-fat diet; this pattern was not observed among NGT. Within IFG, fasting glucose at baseline and the change in fasting glucose over the intervention were inversely associated with baseline PhiD (-0.40, P < .05) and the change in PhiD (-0.42, P < .05), respectively. Eight weeks of a higher-carbohydrate/lower-fat diet resulted in higher insulin sensitivity in healthy, NGT, overweight/obese individuals, and lower fasting glucose and greater glucose-stimulated insulin secretion in individuals with IFG. If confirmed, these results may have an impact on dietary recommendations for overweight individuals with and without IFG.

Fig. 1

Effects of the 8-week diet intervention on A. fasting glucose, B. insulin sensitivity, and C. PhiD. The higher-CHO/lower-fat diet (open bars) was associated with lower fasting glucose (P<0.01) and higher PhiD (P<0.05) within IFG participants (right side), and higher S_I (P<0.05) within NGT participants (left side), relative to the lower-CHO/higher-fat diet (hatched bars). Data adjusted for baseline outcome, gender, and weight change.

Fig. 2

Within IFG, fasting glucose concentration was associated with PhiD both at baseline (A. cross-sectionally; −0.40, P<0.05), and over the course of the intervention (B. change over 8 weeks; −0.42, P<0.05).