Chestnut flour-enriched bread reduces postprandial glycaemic response in healthy adults: a randomised, controlled crossover study.

Elevated postprandial glycaemic excursions contribute to cardiometabolic disease risk, highlighting the importance of dietary strategies to attenuate postprandial glycaemia for prevention. Chestnut (Castanea spp.) is rich in dietary fibre, resistant starch and bioactive (poly)phenols that may modulate carbohydrate digestion, yet evidence in human studies remains limited. We investigated the effects of a chestnut flour-enriched bread on postprandial glycaemic and insulinaemic responses in healthy adults. In a randomised crossover trial, fourteen healthy participants consumed isocaloric meals providing 50 g available carbohydrate as either chestnut flour-enriched bread (50% chestnut flour/50% wheat flour) or control bread (100% wheat flour), following an overnight fast. Capillary blood glucose and insulin were measured over 180 min, and incremental area under the curve (iAUC) was assessed for each. The (poly)phenol composition of the wheat and chestnut flours and the control (wheat only) and chestnut flour-enriched breads was characterised using RP-HPLC-HRFTMS. Chestnut flour-enriched bread, containing (+)-catechin, myricetin, gallic, gentisic and p-coumaric acids (∼480 mg total (poly)phenols), significantly reduced glucose iAUC by 27% compared with control bread (∼100 mg total (poly)phenols) (p = 0.0319, paired t-test; main effects of the meal: p = 0.0243, ANOVA). Glucose concentrations were 16% lower at 120 min (p = 0.0131) and 14% lower at 150 min (p = 0.0071). Total insulin exposure did not differ between the meals, but chestnut enrichment reduced the insulin peak time by approximately 24 min (p = 0.0430). Partial substitution of wheat flour for chestnut flour in bread significantly attenuated postprandial glycaemia in healthy adults, mainly by lowering late-phase glucose excursions without raising insulin demand. These findings support the potential of chestnut flour as a functional ingredient for improving glycaemic control.