Researchers Now Understand Why Astronauts Can't 'Go'

Astronauts' stubborn bowels are finally getting a scientific explanation—and it's about more than bathroom inconvenience. In a NASA-funded study of more than 400 blood samples from 52 astronauts who spent at least two months on the International Space Station, researchers found that life in microgravity appears to slow the movement of food through the intestines, reports Live Science. That gives gut bacteria extra time to chew through fiber and then switch to digesting protein instead—a shift known as protein fermentation. The process, which kicked in within weeks of arriving in orbit and often lasted until astronauts were back on Earth, helps explain why constipation is so common in space, per CNET.

But the study, published in Nature Communications, flags a longer-term concern: Protein fermentation produces compounds such as ammonia and hydrogen sulfide that, in high amounts and over long durations, have been linked to kidney problems, inflammation, and possible effects on mood and concentration. That could pose a risk on future Mars-length missions. Potential fixes under discussion: more dietary fiber, probiotics, and ways to stimulate peristalsis—the gut's muscular conveyor belt—through drugs or even massage.