Short-chain fatty acid kinetics and concentrations are higher after inulin supplementation in young and older adults: a randomized trial

Background

Beneficial short-chain fatty acids (SCFAs) are produced through intestinal microbial fiber fermentation. Using stable tracer methodology and compartmental modeling, we observed lower SCFA production in older (OAs) than in young adults (YAs) in both an accessible [that is, systemic circulation; whole-body production] and inaccessible [potentially representing intestine absorbing microbially produced SCFAs (U₂)] pool.

Objectives

We now investigated whether fiber supplementation increases SCFA production in OAs and whether concentrations reflect production rate changes.

Methods

In this randomized, placebo-controlled, double-blind crossover study, 21 YAs (20–29 y) and 40 OAs (59–87 y) adults were supplemented with inulin or placebo (maltodextrin) for 7 d (final intake: 30 g/d). Before and after interventions, participants collected stool and received an intravenous pulse containing [U-¹³C]-labeled SCFAs followed by blood draws. We measured plasma tracer enrichments, plasma and fecal concentrations by gas chromatography–mass spectrometry and performed compartmental analysis. Data are mean (95% confidence interval).

Results

Inulin evoked a 44% increase in butyrate production (μmol/min) in the inaccessible pool {YA: 28–44 [+16.2 (4.3, 28.1); P = 0.038], OA: 14–20 [+6.1 (2.2, 9.9); P = 0.011]} and were not different between YAs and OAs. In addition, a 34% increase in propionate production in YA only. We found a 50%–60% increase in fecal acetate, propionate, and butyrate and a 34% increase in plasma butyrate in OA, whereas in YA only 34% increase in fecal acetate. Plasma but not fecal concentrations correlated positively with SCFA production in the inaccessible pool (R² = 0.20–0.45; P < 0.001).

Conclusions

OAs have a lower SCFA production. Inulin intake increases SCFA production. Tracer pulse approach detects SCFA metabolism changes more sensitively than plasma or fecal concentration measurements (NCT04459156).