Effectiveness of regular oat β-glucan-enriched bread compared with whole-grain wheat bread on long-term glycemic control in adults at risk of type 2 diabetes: a randomized controlled trial.

Background: A high intake of whole grains is associated with reduced risk of type 2 diabetes and cardiovascular disease, and soluble fiber from oats and barley, that is, β-glucans, has been shown to lower blood cholesterol and postprandial glycaemia. Despite such data and the European Food Safety Authority health claims supporting β-glucan-induced reductions in glucose and cholesterol, effectiveness in real-life settings among individuals at elevated risk of developing type 2 diabetes remains unclear.

Objectives: This study aims to assess the long-term effectiveness of daily consumption of β-glucan-enriched bread, compared with whole-grain wheat bread, on glycated hemoglobin (HbA1c) and glycemic control in adults at risk of type 2 diabetes.

Methods: A 16-wk randomized, double-blind dietary intervention was conducted in 194 adults [58 ± 8 y; BMI: 32 ± 5 kg/m; HbA1c 5.6% ± 0.3% (38 ± 3 mmol/mol); LDL cholesterol 3.6 ± 1.0 mmol/L] across sites in Germany, Norway, and Sweden. Participants consumed ≥3 slices/d of either β-glucan-enriched bread (6 g β-glucan/d) or control bread, 6 d/wk.

Results: After 16 wk, there was no significant between-group difference in HbA1c [Δ = -0.01%, 95% confidence interval (CI): -0.03, 0.06; P = 0.49]. Similarly, no differences were observed in fasting glucose (Δ = -0.02 mmol/L; 95% CI: -0.11, 0.14), insulin (Δ = -0.76 pmol/L; 95% CI: -0.99, 2.5), or LDL cholesterol (Δ = -0.11 mmol/L; 95% CI: -0.27, 0.05) (all P > 0.05).

Conclusions: Contrary to expectations from efficacy studies, this effectiveness trial does not support the metabolic benefits of oat-derived β-glucan-enriched bread under real-life conditions. A simple bread replacement may not be sufficient to improve glucose homeostasis in individuals at risk of type 2 diabetes. This trial was registered with clinicaltrials.gov as NCT04994327.