Astronaut blood metabolites suggest increased gut protein fermentation during spaceflight

University of Copenhagen researchers working with NASA analyzed blood samples from 52 astronauts who spent months aboard the International Space Station. Samples came from three studies conducted across different missions and years. The team used non-targeted metabolomics to identify changes in circulating metabolites during spaceflight, including signals potentially reflecting intestinal bacterial activity.

The analysis indicated increased gut protein fermentation within weeks of arrival in space, with changes persisting until astronauts returned to Earth. Smaller metabolic changes were associated with fish and caffeine consumption. The source provides no numerical effect sizes or statistical estimates. Researchers hypothesize that microgravity slows intestinal transit, allowing bacteria to exhaust available fiber and increasingly ferment protein, potentially contributing to constipation.

These findings could inform research on dietary fiber, prebiotics or treatments that promote intestinal motility during prolonged missions. However, blood metabolites provide indirect evidence of gut processes; the report does not describe direct transit measurements or establish that fermentation caused constipation. Associations between protein-fermentation products and kidney or neurobehavioral effects do not demonstrate such harm in these astronauts. Suggested applications to bedridden patients and proposed countermeasures remain untested in the reported analysis. The account is based on university-provided material rather than a detailed presentation of the primary study.