Increasing plant protein sources in the diet modulates gut microbiota and tryptophan metabolism in men at cardiometabolic risk.

Plain-language summary

This study set out to see how swapping some animal protein for plant protein affects gut bacteria and tryptophan processing in men at risk for heart and metabolic problems. It put 19 men with high triglycerides and waist size on two different diets for a month each: one heavy on plant protein (64%) and another more animal-based (36%). The plant-heavy diet changed certain gut bacteria and shifted how tryptophan was broken down, moving it away from harmful byproducts toward pathways tied to better metabolic health, likely due to the extra fiber from plants.

Key findings

• A flexitarian diet high in plant protein (64%) changed gut bacteria compared to a more animal-based diet (36%).
• The plant-heavy diet increased fecal xanthurenic acid and decreased the potential for harmful indole production.
• The diet shifted tryptophan metabolism toward beneficial pathways like kynurenine and indole propionic acid.
• These changes may be driven by higher fiber intake, particularly from legumes.