Scientists discover why astronauts struggle to poop in space

Astronauts often experience digestive issues in space, specifically constipation, which can be difficult to manage. A new study published in Nature Communications examined how spaceflight affects the human body and gut microbes, potentially explaining why astronauts struggle to pass stool normally. The researchers analyzed blood samples from 52 astronauts who spent between two to nine months aboard the International Space Station.

They tracked changes in hundreds of small molecules produced by the body, food, and gut microbes. The results indicated that microgravity slows down the movement of material through the intestines, causing food and waste to stay in the gut for longer periods. This situation prompts gut microbes to rely more on protein for energy rather than fibre and carbohydrates, leading to the production of compounds that may be harmful.

These compounds, including p-cresol sulfate, phenylacetylglutamine, and 4-ethylphenol sulfate, have been linked with slower intestinal transit in humans. Furthermore, the study revealed that these metabolic changes occurred early on during spaceflight and typically resolved within a few days after landing. While the study does not definitively establish that these compounds are causing disease in astronauts, it suggests that increased protein fermentation could potentially be detrimental to health.

The findings raise concerns for longer-duration missions, such as those to Mars, where astronauts would spend extended periods in space and on the planet. The researchers recommend that diet modifications could help mitigate the issue, as changes in gut microbes' reliance on protein fermentation can be influenced by dietary factors.