Effects of sourdough and yeast fermented breads consumption on glycaemia in healthy populations: a systematic review

Bread is a vital source of energy and is widely consumed in human diets. As a carbohydrate-rich food, it is often considered to impair glycaemic homeostasis; however, clinical and molecular evidence suggest that its effects may vary depending on the characteristics of bread consumed. In particular, sourdough-fermented bread has been proposed to exert potentially beneficial effects on glycaemia via shifts in metabolites in the food matrix, as well as chemical and physical changes that occur during fermentation. However, evidence from human interventional studies on this topic is inconsistent due to differing experimental designs, heterogeneous populations, or a focus on sourdough fermentation that does not consider the effects of yeast fermentation. Our objective was to evaluate the evidence for a positive effect of fermented bread consumption on glycaemia and insulinaemia in healthy adults. To this end, we conducted a systematic review to identify and analyze relevant human studies, complemented by a characterization of the breads investigated and a discussion of possible mechanisms of action, following the EFSA dossier framework. We identified 27 studies that met our inclusion criteria. Taking into account the risk of bias in these studies, the consistency of the reported effects, and the biological plausibility based on food characteristics and potential mechanisms of action, we conclude that the available evidence for a beneficial effect of sourdough compared to yeast-fermented bread on glycaemic and insulinaemic homeostasis in healthy individuals is neither sufficient nor convincing. For the general effect of fermentation on glycaemic and insulinaemic homeostasis in healthy individuals, evidence is considered very low.