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Figure 1. Illustration of potential modulators and general mechanisms influencing gut microbiota composition and host health. Panel (A) illustrates the potential modulators of the human microbiota. Specifically, modulators that promote eubiosis are highlighted in green, while modulators that contribute to dysbiosis are highlighted in red; Panel (B) shows several mechanisms through which bifidobacteria exert beneficial effects on the host. Specifically, bifidobacteria strengthen the intestinal barrier by increasing mucus production and preventing the colonization of opportunistic pathogens, thereby protecting against infections (a). Additionally, bifidobacteria interact with the host’s immune system, stimulating the production of anti-inflammatory cytokines that regulate immune responses and reduce inflammation (b). Bifidobacteria also produce neuroactive molecules, such as GABA, which may influence the nervous system, alleviating stress and supporting mental well-being (c). Furthermore, bifidobacteria generate metabolites like lactate and acetate, which can be utilized by other gut bacteria, such as SCFA-producing bacteria, to synthesize beneficial compounds like butyrate and propionate, contributing to gut health and metabolic regulation (d). GABA: Gamma-aminobutyric acid; SCFA: short-chain fatty acid.