Microbiome byproducts significantly influence the microbial brain-gut axis through diverse mechanisms, including local neurotransmitter production (e.g., norepinephrine), central amino acid synthesis (e.g., tryptophan, tyrosine), short-chain fatty acids (SCFAs), and bile acid derivatives.

These processes can impact brain cell function, cognition, mood, and behavior (Kim, 2024).

SCFA's, primarily acetate, propionate, and butyrate, are generated during the fermentation of dietary fibers by gut bacteria.

They influence central nervous system functions by modulating inflammation, neurogenesis, and neurotransmitter synthesis.

While acetate and propionate are absorbed into the hepatic portal vein and distributed systemically, butyrate primarily fuels colonic cells (Kim, 2024). SCFAs also promote mitochondrial biogenesis and neurogenesis by acting on neural stem cells (Kim, 2024). In rodent studies, SCFA administration has reduced neuroinflammation (Spichak et al., 2021) and alleviated symptoms of autism spectrum disorder (ASD) and Parkinson’s disease (PD), particularly with butyrate.

SCFA production relies on fiber consumption and requires SCFA-producing microbes like Bacteroides, Bifidobacterium, Propionibacterium, Eubacterium, Clostridium, Roseburia, and Prevotella (Kelly et al., 2015).

These microbes thrive on prebiotics such as inulin, fructooligosaccharides, galactooligosaccharides, polyphenols, pectin, and resistant starch. Supporting these microbes underscores the importance of consuming whole grains, legumes, onions, leafy greens, nuts, seeds, spices, and berries.

Thus, nutrition (especially fiber) profoundly shapes the microbial brain-gut axis, emphasizing the role of diet in cognitive and emotional health.