New Study Challenges Assumptions About Single-Food Interventions for Blood Sugar Control in persons at risk of type 2 diabetes

The 16-week randomized controlled trial, known as the CarbHealth study, involved nearly 200 participants across Germany, Norway, and Sweden. Participants were asked to replace their commonly consumed bread with study bread (a ß-glucan enriched or a wholegrain control bread) and to consume at least 3 slices 6 days a week, mimicking real-life conditions.

The study bread was specifically designed at The Norwegian food research Institute (Nofima).  It qualifies for a European Food Safety Authority (EFSA) health claim for foods containing oat beta-glucan that can reduce post-prandial (after-meal) glycemic (blood sugar) responses.

Despite previous evidence from controlled clinical studies suggesting that oat β-glucans can reduce blood glucose and cholesterol levels, this large-scale effectiveness trial found no significant improvements in key metabolic markers such as HbA1c, fasting glucose, insulin, or blood lipids.

“We designed a high-fiber ß-glucan enriched oat bread specifically for this study, aiming to test whether a simple dietary swap could yield measurable health benefits in everyday life,” says professor Jutta Dierkes at the Department of Clinical Medicine.

“However, our findings suggest that changing just one food item—even one with proven short-term benefits—is not enough to improve long-term glycemic control.”

The results contrast with earlier efficacy studies conducted under ideal conditions, which formed the basis for health claims approved by EFSA. These studies showed that β-glucans can lower postprandial blood glucose and cholesterol levels.

The CarbHealth trial, however, highlights the gap between controlled research environments and real-world dietary behavior.

“Our study underscores the importance of a whole-diet approach rather than relying on single-food substitutions,” said co-author Professor Jutta Dierkes. “Even though the oat bread met EFSA’s criteria for β-glucan content, the flexible, real-life consumption patterns likely diluted its potential impact.”

“Functional foods like β-glucan-enriched bread can assist in consuming a healthy diet”, explains associate professor Hanne Rosendahl-Riise at the Department of Clinical Medicine. “yet broader dietary changes as well as environments facilitating healthy choices are needed to achieve meaningful health outcomes”.

Article: https://ajcn.nutrition.org/article/S0002-9165(25)00370-3/fulltext