Overview
- A longitudinal study published June 29, 2026, analyzed 488 plasma samples from 52 astronauts and found blood metabolite patterns that signal gut bacteria moved from fermenting fiber to fermenting protein during missions.
- The metabolic changes emerged within weeks of launch, stayed roughly stable across two- to nine-month missions on the ISS, and mostly reversed within days after astronauts returned to Earth.
- Dietary variation explained about 27.5% of the observed shifts, including drops in caffeine and fish markers, but the remaining changes are consistent with slower gut transit in microgravity rather than diet alone.
- The study is observational so it cannot prove microgravity as the sole cause; authors recommend testing countermeasures such as more slowly fermented carbohydrates (dietary fiber), prebiotics, or pro‑peristalsis treatments in controlled trials.
- Some metabolites elevated in flight have been linked in other research to cell ageing, brain effects, or kidney risk in vulnerable patients, so researchers say the findings matter for astronaut health planning on long missions and may also inform care for bedridden patients on Earth.