Lachnospiraceae in the Food–Gut Axis: A Critical Review of Dietary Modulation, Immune Regulation, and Translational Barriers

The interplay between diet, gut microbiota, and host immunity is central to food science. The Lachnospiraceae family ferments dietary fibers to produce short-chain fatty acids (SCFAs), notably butyrate and propionate, with immunomodulatory potential. This critical review distinguishes established findings from hypotheses. Strain-level functional heterogeneity is substantial; findings from one genus cannot be generalized. Specific substrates (inulin, pectin, resistant starch, and arabinoxylan) and food processing methods shape SCFA profiles. Mechanistically, SCFAs regulate immunity via histone deacetylase inhibition, G-protein-coupled receptor activation, and Treg/Th17 modulation. However, most mechanistic data derive from rodent models; human evidence remains largely correlational and cross-sectional. Three major knowledge gaps exist: the lack of strain-level functional characterization, the absence of causal human intervention trials for the vast majority of Lachnospiraceae strains (with Anaerobutyricum soehngenii being the sole exception, tested only in metabolic disease), and limited translation into food systems. Regulatory barriers (generally recognized as safe [GRAS] status exists only for A. soehngenii CH106 and strictly for food use; no other strain has GRAS or qualified presumption of safety [QPS]), safety concerns (rare opportunistic pathogenicity), and technological challenges (oxygen sensitivity and viability in food matrices) further hinder development. Postbiotics (preparations of inactivated microbial cells or their components) and metabolite-based preparations (e.g., purified SCFAs or fermentation supernatants), alongside synbiotic formulations, offer practical near-term alternatives. Importantly, under the International Scientific Association for Probiotics and Prebiotics (ISAPP) definition, purified metabolites without cellular biomass do not qualify as postbiotics. We conclude that although Lachnospiraceae hold promise for immunomodulatory functional foods, current evidence does not support clinical or commercial claims. Priority research directions include longitudinal human cohorts, strain-level culturomics, and multi-omics integration. This review provides a realistic, food science-centered framework for future investigations.