In vitro digestion under simulated saliva, gastric and small intestinal conditions and fermentation of nicotinamide mononucleotide, and its effects on the gut microbiota

•Nicotinamide mononucleotide (NMN) was slightly digested during in vitro digestion.•NMN was progressively degraded into nicotinamide ribose (NR), nicotinamide (NAM), ribose and niacinate (NA).•NMN was utilized by gut microbiota to promote the production of short chain fatty acids.•NMN significantly improved the composition of the beneficial gut bacteria in both healthy and obese individuals.