Systemic availability and metabolism of colonic-derived short-chain fatty acids in healthy subjects – a stable isotope study

Abstract

The short-chain fatty acids (SCFAs), acetate, propionate and butyrate are bacterial metabolites that mediate the interaction between diet, the microbiota and the host. In this study, the systemic availability of SCFAs and their incorporation into biologically relevant molecules was quantified. Known amounts of ¹³C-labelled acetate, propionate and butyrate were introduced in the colon of 12 healthy subjects using colon delivery capsules and plasma levels of ¹³C-SCFAs and of ¹³C-glucose, ¹³C-cholesterol and ¹³C-fatty acids were measured. The butyrate producing capacity of the intestinal microbiota was quantified as well. Systemic availability of colonic-administered acetate, propionate and butyrate was 36%, 9% and 2%, respectively. Conversion of acetate into butyrate (24%) was the most prevalent interconversion by the colonic microbiota and was not related to the butyrate-producing capacity in the faecal samples. Less than 1% of administered acetate was incorporated into cholesterol and < 15% in fatty acids. On average, 6% of colonic propionate was incorporated into glucose. The SCFAs were mainly excreted via the lungs after oxidation to ¹³CO₂ whereas less than 0.05% of the SCFAs were excreted into urine. These results will allow future evaluation and quantification of SCFAs production from ¹³C-labelled fibres in the human colon by measuring ¹³C-labelled SCFA concentrations in blood.

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