Fiber2026-06

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

Lépine Gaïa, Davila Anne-Marie, Cueff Gwendal, Pickering Gisèle et al. — Gut microbes

Summary

This study explored how swapping some animal protein for plant protein affects gut bacteria and metabolism in men at risk for heart disease. Researchers found that a diet higher in plant protein led to beneficial changes in gut microbes and how the body processes tryptophan, an amino acid, likely due to increased fiber intake from plant foods.

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Key points

Eating more plant protein can lead to beneficial changes in your gut bacteria.
These dietary shifts can influence how your body processes tryptophan, an important amino acid.
The increased fiber from plant foods likely plays a key role in these gut and metabolic changes.
Such dietary adjustments may contribute to better cardiometabolic health.

What the study looked at

This study investigated whether increasing plant protein intake could positively impact gut health and metabolism in men at higher risk for heart disease and diabetes. **What question did this study ask?** Researchers wanted to know if replacing some animal protein with plant protein could change the gut bacteria and how the body uses certain nutrients in men who have a higher risk of heart disease and diabetes. **How was the study designed and who participated?** The study involved 19 men with elevated triglycerides and a larger waistline, factors linked to cardiometabolic risk. They followed two different diets, each for four weeks, in a crossover design: one diet was rich in plant proteins (flexitarian), and the other had more animal protein. Scientists then analyzed their gut bacteria and various metabolic markers in stool and blood samples. **What did the study find?** The findings showed that the plant-heavy diet led to specific shifts in the types of bacteria living in the gut. It also altered how the body processed tryptophan, an essential amino acid, moving it towards pathways that are potentially more favorable for health. These changes were likely influenced by the higher fiber content found in plant-based foods, especially legumes.

Dietary takeaway

Incorporating more plant-based protein sources like beans, lentils, nuts, and whole grains into your daily meals can naturally increase your dietary fiber intake. This study suggests such a shift might positively influence your gut health and metabolism. However, it's important to remember that this is just one study, and more research is needed to draw definitive conclusions about long-term health benefits.

Abstract

This study investigated the effect of partially substituting dietary animal with plant protein (PP) sources on the fecal microbiota composition and metabolome in men with increased cardiometabolic risk. In a randomized, controlled, crossover feeding trial (NCT04236518), 19 men with high plasma triglycerides and waist circumference completed two 4-week isoenergetic diets: a flexitarian diet high in PP sources (FLEX, 64% PP) and a more animal-based control diet (CON, 36% PP). Fecal microbiota (shotgun metagenomics: taxa and metabolic pathways) and metabolome (targeted LC-MS) profiles were assessed before and after each diet and integrated with the host plasma metabolome. Delta values (Δ) were computed ( = 15 participants with all samples available), inter-individual variation was extracted to account for cross-over design, and OPLS-DA analyses comparing FLEX and CON Δ were performed. Variables were selected based on their contribution to the diet discrimination effect (VIP > 1.5) and significant differences between groups (-value < 0.05 from the paired Wilcoxon signed-rank test). The gut microbiota diversity remained unchanged, but FLEX reduced taxa associated with animal-based diets (e.g., ). Compared to CON, FLEX increased fecal xanthurenic acid and decreased the genetic potential for indole production. Combined with previously reported plasma changes (increased indole propionic acid and decreased indoxyl sulfate after FLEX), these findings suggest a shift away from indole production toward kynurenine and indole propionic acid-related tryptophan pathways, possibly driven by higher fiber intake, particularly from legumes. A one-month flexitarian diet thus modulated in men specific microbial taxa and metabolism, particularly tryptophan catabolism. These coordinated changes in microbial composition, functional potential, and metabolites indicate that diets higher in PP sources influence gut microbiota activities relevant to cardiometabolic health.

View on PubMed →DOI: 10.1080/19490976.2026.2677951