Scientists identify why astronauts often struggle with bowel movements in space
A NASA-backed study has found that microgravity alters astronauts' gut bacteria, causing constipation that could pose greater health risks on future long-duration Mars missions.
Constipation is a fairly common problem among astronauts, and a new NASA-supported study now offers a possible explanation. Researchers analyzed more than 400 blood samples from 52 astronauts who had spent at least two months aboard the International Space Station between 2006 and 2018.
Gut bacteria shift their behavior
Scientists searched the blood samples for metabolites — compounds produced during the body's metabolic processes — and identified 40 significant compounds, many linked to how gut bacteria break down protein. Within just a few weeks in space, astronauts' gut bacteria began processing more protein instead of relying mainly on complex carbohydrates and fiber, as they typically do on Earth. Researchers attribute this to microgravity, which appears to slow the movement of food through the intestines.
Dietary changes in space, including shifts in caffeine, fish and fat intake, may also play a role. However, diet accounts for less than a third of the observed metabolite changes, leading researchers to conclude that microgravity is the primary driver.
Potential health risks
What concerns scientists most is that increased protein fermentation produces byproducts such as ammonia and hydrogen sulfide, which have been linked to kidney damage, mood changes, reduced concentration, and gut inflammation. On short missions these effects are unlikely to pose a serious risk, but on longer missions, such as a journey to Mars, the buildup of these compounds could become more concerning.
Possible countermeasures for future missions include a higher-fiber diet, probiotics, and methods to stimulate intestinal peristalsis, potentially through medication or massage. Researchers note that current data mainly reflects stays aboard the space station, and it remains unclear how the issue might evolve during much longer flights.
The findings could also have relevance on Earth, as similar changes in gut function may occur in people who are bedridden or largely sedentary for extended periods.
