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 wholegrain 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 6 13 years old, BMI 32.4 6 7 kg/m 2 , HbA 1c 7.5 6 3.4% [59 6 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 (20.16 mmol/L [95% CI 20.25 to 20.06]) and mean amplitude of glycemic excursion (20.36 [95% CI 20.65 to 20.08]). 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.

The gut microbiota plays a fundamental role in human nutrition and metabolism and may have direct implications for type 2 diabetes and associated pre-conditions. An improved understanding of relationships between human gut microbiota and glucose metabolism could lead to novel opportunities for type 2 diabetes prevention, but human observational studies reporting on such findings have not been extensively reviewed. Here, we review the literature on associations between gut microbiota and markers and stages of glucose dysregulation and insulin resistance in healthy adults and in adults with metabolic disease and risk factors. We present the current evidence for identified key bacteria and their potential roles in glucose metabolism independently of overweight, obesity and metabolic drugs. We provide support for short-chain fatty acids (SCFA) mediating such effects and discuss the role of diet and gut microbiota x diet derived metabolites. From 5983 initially identified PubMed records, 45 original studies were eligible and reviewed. Alpha diversity and 45 bacterial taxa were associated with selected outcomes. Six taxa were most frequently associated with glucose metabolism: Akkermansia muciniphila, Bifidobacterium longum, Clostridium leptum group, Faecalibacterium prausnitzii and Faecalibacterium (inversely associated) and Dorea (directly associated). For Dorea and A. muciniphila, associations were independent of metabolic drugs and body measures. For A. muciniphila and F. prausnitzii, limited evidence supported SCFA-mediation of potential effects on glucose metabolism. We conclude that observational studies applying metagenomics sequencing to identify species-level relationships are warranted, as are studies accounting for confounding factors and investigating SCFA and postprandial glucose metabolism. Such advances in the field will, together with mechanistic and prospective studies and investigations into diet-gut microbiota interactions, have the potential to bring critical insight into roles of gut microbiota and microbial metabolites in human glucose metabolism and to contribute towards the development of novel prevention strategies for type 2 diabetes, including precision nutrition.

<b>Objective:</b> To consider the effects of wholegrain processing, specifically milling, on glycaemic control in free-living adults with type 2 diabetes. <p><b>Research Design and Methods:</b> Participants of this crossover trial were randomised to two interventions of two-weeks, separated by washout. They were advised to replace the grain foods they normally consumed with intervention foods. Intervention foods were nutrient matched wholegrain 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 wholegrain intake) were measured pre and post interventions. </p> <p><b>Results:</b> 31 adults with type 2 diabetes (63±13 years old, BMI 32.4±7, HbA1_c 7.5±3.4% (59±14mmol/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% (95%CI 1-10%) lower following all meals of less processed whole grains when compared with finely milled grains. Day-long glycaemic variability also reduced when measured by 24-hour standard deviation (-0.16mmol/l 95%CI -0.25 to -0.06) and MAGE (-0.36 95%CI -0.65 to -0.08). Mean change in body weight differed by 0.81kg (95%CI 0.62 to 1.05) between interventions, increasing during the finely milled intervention and decreasing during the less processed wholegrain intervention. This was not a mediating factor for the glycaemic variables considered.</p> <b>Conclusions:</b> Consuming less processed wholegrain foods over two weeks improved measures of glycaemia in free-living adults with type 2 diabetes when compared with an equivalent amount of wholegrain foods that were finely milled. Dietary advice should promote the consumption of minimally processed whole grains.

<b>Objective:</b> To consider the effects of wholegrain processing, specifically milling, on glycaemic control in free-living adults with type 2 diabetes. <p><b>Research Design and Methods:</b> Participants of this crossover trial were randomised to two interventions of two-weeks, separated by washout. They were advised to replace the grain foods they normally consumed with intervention foods. Intervention foods were nutrient matched wholegrain 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 wholegrain intake) were measured pre and post interventions. </p> <p><b>Results:</b> 31 adults with type 2 diabetes (63±13 years old, BMI 32.4±7, HbA1_c 7.5±3.4% (59±14mmol/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% (95%CI 1-10%) lower following all meals of less processed whole grains when compared with finely milled grains. Day-long glycaemic variability also reduced when measured by 24-hour standard deviation (-0.16mmol/l 95%CI -0.25 to -0.06) and MAGE (-0.36 95%CI -0.65 to -0.08). Mean change in body weight differed by 0.81kg (95%CI 0.62 to 1.05) between interventions, increasing during the finely milled intervention and decreasing during the less processed wholegrain intervention. This was not a mediating factor for the glycaemic variables considered.</p> <b>Conclusions:</b> Consuming less processed wholegrain foods over two weeks improved measures of glycaemia in free-living adults with type 2 diabetes when compared with an equivalent amount of wholegrain foods that were finely milled. Dietary advice should promote the consumption of minimally processed whole grains.