Observational studies suggest diets high in whole grains (WG) may confer metabolic benefits over diets based on refined grains (RG) for overweight/obese individuals, thus preventing the development of type 2 diabetes (T2D). However clinical data have been inconclusive, in part due to metabolic heterogeneity. Therefore, we investigated a WG and RG diet in individuals at high risk (HR) or low risk (LR) of developing T2D based on 1 hour glycemic level during an OGTT (oral glucose tolerance test). We conducted a double-blind randomized crossover trial in 15 overweight/obese adults. Participants were administered a 4 hour, 75g OGTT and stratified as HR or LR of developing T2D (HR: 1 hour OGTT glucose (GLU) ≥155 mg/dl; LR: 1 hour OGTT GLU <155 mg/dl). Isocaloric WG and RG diets were provided for two 8 week periods with 10 week washout. Macronutrients were matched except for WG or RG (50g/1000 kcal). Fifteen subjects completed the trial, 10 HR (38±3 years, 33±2 kg/m2, 1 hour OGTT GLU 201±8 mg/dl) and 5 LR (38±4 years, 35±2 kg/m2, 1 hour OGTT GLU 126±5 mg/dl). Groups differed only by 1 hour OGTT (p<0.05). Weight loss was similar but only HR reached statistical significance (-2.1 kg, p<0.05). HR-WG improved insulin sensitivity (Matsuda Index, +21%, p<0.05). Further, HR-RG had a significant negative association between change in BMI and Matsuda Index vs. WG (r2=0.41, p<0.01). LR-RG reduced GLU clearance (iAUC 180 minutes, +27%, p<0.05 vs. WG). In agreement, LR-RG increased OGTT insulin (iAUC p<0.05 at 120, 180 and 240 minutes) and c-peptide (iAUC p<0.05 at 60 and 120 minutes). Interestingly, 1 hour OGTT GLU predicted change in waist circumference in WG (n=15, r2=0.36, p=0.02), suggesting those with more impaired GLU tolerance may acquire greater benefit from WG. We observed differential effects of a WG and RG diet in overweight/obese adults. These data suggest a WG diet may improve measures of glucose metabolism in individuals at high risk of developing T2D, whereas a RG diet may impair glucose metabolism in lower risk individuals.
J.T. Mey: None. A. Hari: None. J. Godin: Employee; Self; Nestlé. Employee; Spouse/Partner; Nestlé. A. Ross: None. J.P. Kirwan: None.