The Study
Effect of short-term dietary intervention on fecal serotonin, gut microbiome-derived tryptophanase, and energy absorption in a randomized crossover trial: an exploratory analysis
This study watched what happened to 15 healthy people when they ate more, less, or just enough food for a few days. It found that their poop chemicals and gut bacteria changed — but it didn't prove that one thing caused another, just that they changed together.
Analysis score
Maximum 90 for a randomized controlled trial.
Where the score came from
When people ate extra food for 8 days, their gut bacteria made less of a chemical linked to serotonin, and their bodies absorbed more energy from food.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 568 / 100
Quality score
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
Key takeaways
Summary
Based on the study abstract and findings.
- 1Yes — eating more food may cause your gut microbes to change in ways that help your body pull more calories out of food, potentially making weight gain easier.
- 2Overfeeding reduced fecal serotonin by 0.005–0.001 p-values, increased energy absorption by 3–15%, and shortened gut transit time by 1–2 days.
- 3Bacteroides bacteria and tryptophanase genes dropped during overfeeding.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
Gut Microbes
Year
2025
Authors
E. Yoshimura, Yuka Hamada, Yoichi Hatamoto, T. Nakagata, H. Nanri, Yui Nakayama, Chiharu Iwasaka, Takanori Hayashi, Ippei Suzuki, Takafumi Ando, K. Ishikawa-Takata, Shigeho Tanaka, Rei Ono, Michihiro Araki, Hitoshi Kawashima, Yi-An Chen, Jonguk Park, Koji Hosomi, Kenji Mizuguchi, J. Kunisawa, M. Miyachi
Related Content
Claims (6)
Changes in diet or supplements can cause measurable changes in the types and amounts of bacteria in the gut within a few days.
When healthy young adults consume excess calories for eight days, their fecal serotonin levels drop compared to those on normal or reduced calorie diets, and this drop coincides with lower levels of Bacteroides bacteria and its tryptophanase enzyme.
When healthy young adults consume more calories than needed for a short time, their bodies absorb more usable energy from food than when they eat normal or reduced amounts.
In healthy young adults, higher levels of Bacteroides bacteria in the gut are consistently linked to higher activity of the tryptophanase gene, indicating a relationship between this bacterium and the breakdown of tryptophan by gut microbes.
When healthy young adults eat more calories than needed for a short time, food moves through their digestive tract faster, and this is linked to changes in fecal serotonin and Bacteroides bacteria levels.
In healthy young adults, larger fluctuations in fecal serotonin levels during overeating are linked to higher amounts of energy absorbed from food.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.