From Digestion to Colonic Fermentation: How Plant-Based Proteins Shape Gut Microbiota Composition and Function

It is estimated that over 90% of dietary proteins are digested in the small intestine, but factors such as protein quantity and source, especially for plant proteins, can significantly influence the amounts reaching the colon. There is growing evidence that dietary proteins play a critical role in shaping the gut microbial ecosystem and, consequently, host health. This is because undigested proteins serve as substrates for colonic fermentation, thereby reshaping microbial composition and modulating the production of metabolites that can exert both beneficial and potentially deleterious effects on intestinal and systemic health. While there is evidence suggesting that higher animal meat intake, particularly processed red meat, can modify gut microbiota composition and function, it remains unclear to what extent different sources, forms, and levels of plant-based protein intake influence the gut microbiota. This review outlines the fate of plant proteins in the gastrointestinal tract, discusses factors influencing their transit into the colon, and examines the impact of protein quantity, source, and form on gut microbiota composition and metabolic activity. We also present major open questions important to understanding the health outcomes mediated by the crosstalk between plant proteins and gut microbiota.