(P27-11-26) The Effects of Fresh Watermelon Consumption on Gut Microbiome in Adults With Overweight and Obesity

Objectives: The gut microbiome plays a vital role in digestion, immune regulation, and metabolic health, and is strongly influenced by diet. Watermelon contains bioactive compounds, including L-citrulline, which may benefit vascular and gastrointestinal health. However, the effects of watermelon consumption on the human gut microbiome remain poorly understood. The objective of this study was to investigate whether daily watermelon consumption favorably alters gut microbiome composition and bowel movement habits in individuals with overweight and obesity, compared with a calorie-matched control snack.

Methods: In a randomized, 4-week crossover trial, 32 adults with overweight/obesity consumed either fresh watermelon (330 g/day) or a low-fat cookie control (22.7 g/day), separated by a 4-week washout period. Stool samples collected at baseline and week 4 of each intervention underwent 16S rRNA sequencing to assess alpha and beta diversity, differential taxa changes, and relative abundance. Bowel movement habits were evaluated using a 7-day bowel movement questionnaire at baseline and week 4 of each intervention.

Results: Alpha and beta diversity did not differ significantly between interventions. The Firmicutes-to-Bacteroidetes ratio increased in the control group (P=0.021) but not in the watermelon group. In the watermelon intervention, Acetanaerobacterium elongatum and Intestinimonas butyriciproducens increased (P < 0.05), species linked with acetate and butyrate production and beneficial glucose and immune functions. Several species, including Alistipes onderdonkii and Ruminococcus champanellensis, which have been linked to improved glucose regulation, also decreased. The control intervention also produced increases in several species associated with positive metabolic or anti-inflammatory effects, making attribution of changes solely to watermelon difficult. No significant differences were observed in bowel movement habits.

Conclusions: Daily watermelon consumption produced increases in microbial species associated with improved metabolic and immune function; however, similar beneficial shifts were observed in the calorie-matched control group. Further research is needed to clarify watermelon-specific contribution to gut microbial changes.

Funding Sources: Supported by the National Watermelon Promotion Board