Impact of minimally processed versus milled whole grains on glycaemic control in type 2 diabetes: A 12-week...

Whole grains are widely promoted within a healthy diet, with dietary advice encouraging the replacement of refined grains with whole grains. However, data from small trials indicates that milling or processing whole grains may influence the glycaemic response.

To identify if clinically relevant HbA1c differs with processed (milled) or less processed (unmilled) whole grain intakes in type 2 diabetes management.

We conducted a 12-week randomised parallel trial in adults with type 2 diabetes. Participants received free and delivered whole grain foods that differed in degree of processing. Each intervention was of four foods from whole grain wheat, rice, and oats, in sufficient amounts (4.5-9kg per fortnight) to accommodate family size. Participants were advised to replace the grain foods they normally consumed with the provided products. The primary outcome was glycated haemoglobin (HbA1c). All analyses were performed using an intention-to-treat approach, with outcome variables investigated using a generalised linear model.

160 adults with type 2 diabetes (mean age 58.5 ± 11.5 years; BMI 33.7 ± 7.3 kg/m²; HbA1c 56.4 ± 14.3 mmol/mol) were randomised, with 143 (89%) providing end-of-intervention blood samples. HbA1c was lower following the less processed whole grain intervention compared with the more processed whole grain intervention (mean difference -2.2 mmol/mol, 95% CI -4.2, -0.1), despite no change observed in body weight between interventions. Whole grain, refined grain, and nutrient intakes did not differ between groups, with intervention foods providing approximately 20% of dietary energy. Among the secondary or exploratory outcomes, improvements were indicated only in self-reported bowel habits with less processed whole grains.

Less processed whole grain foods were associated with improved glycated haemoglobin compared with more processed whole grain foods in adults with type 2 diabetes. These findings indicate that the degree of grain processing influences metabolic outcomes, support food reformulation, and distinguishing between refined grains, milled whole grains (wholemeal), and intact whole grains in dietary guidance, food marketing and labelling.

ACTRN12622000060741.