Slower Eating Prolongs Intestinal Transit Time and Reduces Fecal Short-Chain Fatty Acids in Healthy Men: A Preliminary Randomized Crossover Trial.

BACKGROUND & AIMS: Fast eating is associated with obesity and metabolic disorders; however, the underlying physiological mechanisms remain unclear. This study investigated whether eating speed affects energy absorption, intestinal transit time, gut microbiota composition, and microbial fermentation in healthy men.

METHODS

In this randomized crossover trial, eight healthy men completed two 8-day interventions separated by a washout period of ≥3 weeks: a fast-eating condition (60% of usual eating time) and a slow-eating condition (200% of usual eating time). All meals were standardized across both interventions. Digestible energy intake (DEI), metabolizable energy intake (MEI), gastric emptying, intestinal transit time, gut microbiota composition, and fecal and circulating short-chain fatty acids (SCFAs) were assessed.

RESULTS

Compared with fast eating, slow eating significantly increased meal duration and chewing frequency (both p < 0.001). DEI (95.0% vs. 94.7%, p = 0.269) and MEI (92.2% vs. 91.8%, p = 0.237) did not differ between conditions. Gastric emptying parameters, gut microbiota diversity, and microbial composition also remained unchanged. However, intestinal transit time was significantly longer during slow eating (35.1 ± 9.1 h vs. 25.7 ± 5.1 h, p = 0.025). Total fecal SCFAs concentrations were significantly lower during slow eating (p = 0.015), primarily because of reduced acetic acid (p = 0.012) and butyric acid (p = 0.029) concentrations. Circulating SCFAs concentrations did not differ between conditions. Additionally, changes in fecal SCFAs concentrations were strongly associated with changes in fecal moisture content (rs = 0.857, p=0.011).

CONCLUSION

Under controlled dietary conditions, slower eating did not affect energy absorption efficiency, gastric emptying, or overall gut microbiota composition. However, it significantly prolonged intestinal transit time and reduced fecal SCFAs concentrations. These findings suggest that eating speed may influence intestinal transit and fecal SCFAs concentrations without substantially affecting digestive efficiency or overall gut microbiota composition.