Tracing the pathway from plate to bloodstream
The prebiotic-to-SCFA pathway has clear steps. Fermentable fiber survives the upper gut, colonic bacteria ferment it to short-chain fatty acids (butyrate, propionate, acetate), and these acids then act locally and systemically. Butyrate is consumed largely by colonocytes as fuel, propionate is mostly cleared by the liver where it can influence glucose handling, and acetate enters general circulation.
Each acid has a somewhat different fate, so the mix produced shapes which downstream effects predominate.
Immune signaling and the gut-brain connection
SCFAs do more than feed cells. They bind receptors such as GPR43 and GPR41 on gut and immune cells and inhibit histone deacetylases, which can promote regulatory T cells and support an anti-inflammatory tone. Some SCFAs and related signals also reach the brain via the bloodstream and vagal pathways, one node of the gut-brain axis.
Most of this detail comes from cell and animal studies; human effects are real but more modest and variable. This is general educational information, not medical advice.