The prebiotic inulin improves substrate metabolism and promotes short-chain fatty acid production in overweight to obese men

Abstract

Background and Aims

Human gut microbiota play an important role in maintaining human health. Dietary fibers, i.e. prebiotics, are fermented by human gut microbiota into the short-chain fatty acids (SCFAs) acetate, propionate, and butyrate. SCFAs promote fat oxidation and improve metabolic health. Therefore, the prebiotic inulin might be an effective dietary strategy to improve human metabolism. We aimed to investigate the acute metabolic effects of ingesting inulin compared with digestible carbohydrates and to trace inulin-derived SCFAs using stable isotope tracer methodology.

Methods

In a double-blind, randomized, placebo-controlled crossover design, 14 healthy, overweight to obese men consumed a high-fat milkshake containing A) 24 g inulin of which 0.5 g was U-¹³C-inulin (INU) or B) 24 g maltodextrin placebo (PLA), with a wash-out period of at least five days. Fat oxidation was measured via an open-circuit ventilated hood and blood samples were collected up to 7 h after ingestion. Plasma, breath, and fecal samples were collected, and appetite and satiety scores were assessed.

Results

Fat oxidation increased in the early postprandial phase (0−3 h), and both plasma glucose and insulin were lower after INU ingestion compared with PLA (all P < 0.05). Plasma free fatty acids were higher in the early, and lower in the late postprandial period after INU ingestion. Inulin was fermented into SCFAs as indicated by higher plasma acetate concentrations after INU compared with PLA (P < 0.05). In addition, we found continuous increases in plasma ¹³C-SCFA enrichments (P < 0.05 from t = 120 onwards) and breath ¹³CO₂ enrichments after INU intake. There were no effects on plasma triglycerides, free glycerol, satiety hormones GLP-1 and PYY, and appetite and satiety scores.

Conclusions

Ingestion of the prebiotic inulin improves fat oxidation and promotes SCFA production in overweight to obese men. Overall, replacing digestible carbohydrates with the fermentable inulin may favor human substrate metabolism.

Clinical Trial Registry

The trial was registered at clinicaltrials.gov under number NCT02009670.