Whole-Grain Processing and Glycemic Control in Type 2 Diabetes: A Randomized Crossover Trial

OBJECTIVE To consider the effects of whole-grain processing, specifically milling, on glycemic control in free-living adults with type 2 diabetes. RESEARCH DESIGN AND METHODS Participants of this crossover trial were randomized to two interventions of 2 weeks, separated by washout. They were advised to replace the grain foods they normally consumed with intervention foods. Intervention foods were nutrient-matched whole-grain products of wheat, oats, and brown rice that differed in their degree of processing. No other lifestyle advice was given. Continuous glucose monitoring systems were worn. Other cardiometabolic risk factors and alkylresorcinols (a biomarker of whole-grain intake) were measured pre- and postintervention. RESULTS Thirty-one adults with type 2 diabetes (63 ± 13 years old, BMI 32.4 ± 7 kg/m2, HbA1c 7.5 ± 3.4% [59 ± 14 mmol/mol]) commenced the trial; 28 (90%) completed both interventions. The increase in alkylresorcinols did not differ between interventions, and there was no difference in reported energy intake. Postprandial responses were 9% (95% CI 3–15) lower following breakfast and 6% (1–10) lower following all meals of less-processed whole grains when compared with finely milled grains. Day-long glycemic variability also was reduced when measured by 24-h SD (−0.16 mmol/L [95% CI −0.25 to −0.06]) and mean amplitude of glycemic excursion (−0.36 [95% CI −0.65 to −0.08]). Mean change in body weight differed by 0.81 kg (95% CI 0.62–1.05) between interventions, increasing during the finely milled intervention and decreasing during the less-processed whole-grain intervention. This was not a mediating factor for the glycemic variables considered. CONCLUSIONS Consuming less-processed whole-grain foods over 2 weeks improved measures of glycemia in free-living adults with type 2 diabetes compared with an equivalent amount of whole-grain foods that were finely milled. Dietary advice should promote the consumption of minimally processed whole grains.