Can low-fiber or low-plant-diversity eating patterns shift the gut microbiome toward less favorable metabolites and inflammation-related signaling?

Low-fiber and low–plant-diversity patterns are credibly associated with gut microbial features linked to less favorable metabolite production and inflammation-related signaling. The evidence is moderate in confidence and primarily observational, so these patterns indicate risk associations rather than deterministic effects.

Microbial-metabolite evidence

• In the American Gut cohort, eating >30 distinct plant foods/week was associated with greater bacterial and metabolome alpha diversity and enrichment of putative SCFA-producing taxa, including Faecalibacterium prausnitzii and Oscillospira. Lower plant diversity therefore plausibly provides less support for these functions.
• Among older adults, a healthful plant-based pattern was associated with greater microbiome evenness, more polysaccharide-degrading species, and lower plasma trimethylamine N-oxide (TMAO); unhealthful plant-based patterns showed opposite or null associations.
• An intervention targeting ≥30 plant foods/week increased butyrate and isobutyrate production in adults with moderate chronic kidney disease. However, SCFA changes vary substantially with fiber type, dose, food matrix, intervention duration, and baseline microbiota; TMAO is also influenced by overall diet and kidney function.

Inflammation-related signaling and mechanisms

• In a prospective cohort of 307 generally healthy men, higher fiber intake—particularly fruit-derived pectin—was associated with carbohydrate-degrading taxa and lower circulating C-reactive protein (CRP); the inverse pattern linked lower fiber with higher CRP.
• Across four cohorts, diets richer in legumes, whole grains, nuts, and vegetables were associated with more SCFA-producing microbes, fewer pathobionts, and lower intestinal inflammatory markers.
• Mechanistically, microbial fiber fermentation produces SCFAs, which plausibly support epithelial-barrier integrity and immune regulation. Effects differed by Prevotella copri carriage, underscoring individualized microbial responses.

Bottom line

• Low fiber and probably low plant diversity are associated with a less favorable microbial-metabolic and inflammatory profile. For a 71-year-old man, increasing the variety of fiber-containing plant foods is a biologically plausible strategy, but expected biomarker or microbiome changes should not be assumed to be uniform.