Influence of Barley Grain Architecture on Colonic Fermentation and Metabolism: A Narrative Review

The human health effects of barley are considered to arise mainly from its undigested carbohydrates, yet how its grain composition translates to physiological effects is not fully understood. Most studies focus on total dietary fibre content rather than on how carbohydrates are arranged within the grain, leaving open questions about how barley grain structure may influence fermentation within the colon. The organisation of cell walls, starch granules, and the surrounding non-starch polysaccharides decides what escapes digestion in the gastrointestinal tract and is therefore accessible to gut microbes during colonic fermentation. This narrative review explores how barley grain morphology may influence the onset, duration, and location of gut fermentation, and how this may affect metabolic pathways. Therefore, we propose hypotheses linking processing formats to fermentation patterns and host signalling, aiming to address clear gaps in our understanding of this area. Closing these gaps could enable processing strategies that modulate colonic fermentation dynamics and target specific colonic responses.