High-protein diets increase microbiota associated p-cresol production in the colon and reduce gut barrier function in a sex-dependent manner.

Protein is an essential nutrient, but the detrimental effects of excess dietary protein on gut health are often overlooked. Protein fermentation by colonic microbiota may impair barrier function by increasing toxic metabolite production. We previously identified sex-by-protein interactions affecting the microbiota and its metabolites in vitro. Do sex-by-protein interactions in colonic protein fermentation lead to a sexually dimorphic response in gut barrier function in vivo? We hypothesised that high-protein diets would elicit sex-specific effects on microbiota and barrier function. Twenty sibling-matched male (n = 10) and female (n = 10) piglets were fed high-protein (28%) or standard-protein (SP; 18%) diets for four weeks. Bacterial populations were assessed using 16 S rRNA sequencing, urinary metabolites via SPME/GC-MS, and gut barrier proteins via quantitative fluorescence immunohistology. High-protein diets increased bacteria-derived p-cresol and reduced E-cadherin and CD45 + protein expression without altering microbiota composition. Females on high-protein diets had greater abundances of Staphylococcus and Chryseobacterium, elevated p-cresol, and reduced ZO-1 expression compared to males. High-protein diets appear to reduce barrier function and increase protein-associated toxic metabolite production in sexually dimorphic manners in pigs. If these results are replicated in humans, it indicates requirements for sex-specific nutritional strategies.