Food starch structure impacts gut microbiome composition

Starch is a major energy source for the human diet and is consumed in diverse forms. Resistant starch (RS) escapes small intestinal digestion and is fermented in the colon by the resident microbiota, with beneficial impacts on colonic function and host health, but the impacts of the micro- and nano-scale structure of different physical forms of food starch on the broader microbial community have not previously been described. Here, we use a porcine in vitro fermentation model to establish that starch structure dramatically impacts microbiome composition, including the key amylolytic species, and markedly alters both digestion kinetics and fermentation outcomes. We show that three characteristic food forms of starch that survive digestion in the small intestine each give rise to substantial and distinct changes in the microbiome, and fermentation products. Our results highlight the complexity of starch fermentation processes, and indicate that not all forms of RS in foods are degraded/fermented in the same way. This work points the way for the design of RS tailored degradation by defined microbial communities, informed by an understanding of how substrate structure influences the gut microbiome, to improve nutritive value and/or health benefits.