Discovering a new paradigm: Gut microbiota as a central modulator of sexual health

Table 1 Short-chain fatty acids: Composition, absorption, and circulatory levels

Short-chain fatty acid	Relative abundance (%)	Fecal concentration (g/kg)	Main absorption route	Plasma concentration (μM)	Biological function
Acetate	About 60%	About 60 g/kg	Absorbed via MCTs in the colon; partially crosses the BBB	100-200	Primary energy source for peripheral tissues, precursor for lipogenesis, contributes to appetite regulation and gut-brain communication
Propionate	About 20%	About 10-20 g/kg	Mainly used by hepatocytes, with a small fraction entering the circulation	1-15	Plays a crucial role in hepatic gluconeogenesis and cholesterol metabolism, modulates inflammatory pathways
Butyrate	About 20%	About 3.5-32.6 g/kg	Primary energy source for colonocytes; also crosses the BBB	1-15	Essential for maintaining gut barrier integrity, possesses anti-inflammatory and neuroprotective properties

MCTs: Monocarboxylate transporters; BBB: Blood-brain barrier.