Effectiveness of Regular Oat β-Glucan Enriched Bread Compared to Whole Grain Wheat Bread on Long-Term Glycemic Control in Adults at Risk of Type 2 Diabetes: A Randomized Controlled Trial

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, i.e. β-glucans, have been shown to lower blood cholesterol and postprandial glycemia. Despite such data and the European Food Safety Authority (EFSA) 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. To assess the long-term effectiveness of daily consumption of β-glucan enriched bread, compared to whole-grain wheat bread, on glycated hemoglobin (HbA1c) and glycemic control in adults at risk of type 2 diabetes. A 16-week randomized, double-blind dietary intervention was conducted in 194 adults (58 ± 8 years; Body Mass Index (BMI) 32 ± 5 kg/m2; HbA1c 5.6 ± 0.3% (38 ± 3 mmol/mol); Low-Density Lipoprotein (LDL)-cholesterol 3.6 ± 1.0 mmol/L) across sites in Germany, Norway, and Sweden. Participants consumed at least 3 slices/day of either β-glucan enriched bread (6 g β-glucan/day) or control bread, 6 days/week. After 16 weeks, there was no significant between-group difference in HbA1c (Δ = -0.01%, 95% CI: -0.03 to 0.06; p = 0.49). Similarly, no differences were observed in fasting glucose (Δ = -0.02 mmol/L, 95% CI: -0.11 to 0.14), insulin (Δ = -0.76 pmol/L, 95% CI: -0.99 to 2.5), or LDL-cholesterol (Δ = -0.11 mmol/L, 95% CI: -0.27 to 0.05) (all p > 0.05). Contrary to expectations from efficacy studies, this effectiveness trial did not support 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. ClinicalTrials.gov (NCT04994327).