Mixed
Long-term adherence to agrarian diets high in plant-based fiber increases gut microbial diversity and short-chain fatty acid (SCFA) production, whereas Western-style diets low in fiber decrease beneficial Firmicutes and increase pathogenic Proteobacteria.
Prioritize a diet rich in diverse plant fibers (fruits, legumes, whole grains) to support a diverse microbiome and high SCFA production. Avoid long-term adherence to Western-style diets high in fat/sugar and low in fiber, as these reduce beneficial bacteria and increase pathogenic risks. Note that short-term extreme low-carb diets may negatively impact microbiota diversity and SCFA levels.
Agrarian diets high in fruit/legume fibre are associated with greater microbial diversity and a predominance of Prevotella over Bacteroides. ‘Western’-style diets, high in fat/sugar, low in fibre, decrease beneficial Firmicutes that metabolise dietary plant-derived polysaccharides to SCFAs and increase mucosa-associated Proteobacteria (including enteric pathogens).
Why this rating
Based on multiple cross-sectional population studies (De Filippo, Yatsunenko, Wu) and controlled intervention studies showing consistent trends, though causality in observational studies is limited.
Source
Review article: dietary fibre-microbiota interactions
Hannah L. Simpson et al. · Alimentary Pharmacology & Therapeutics · 2015
DOI 10.1111/apt.13248
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