Researchers have identified the biological mechanisms behind a common problem astronauts face during spaceflight: constipation. A new study published in Nature Communications analyzed blood samples from 52 International Space Station crew members who spent extended periods in orbit between 2006 and 2018, revealing unexpected changes in how their bodies process food.
Scientists discovered that microgravity causes food to move more slowly through the digestive tract, allowing gut bacteria to break down fiber completely before turning to protein fermentation instead. This metabolic shift produces compounds including ammonia and hydrogen sulfide, which appear in blood tests within weeks of arrival in space and persist until astronauts return to Earth. While these changes explain the constipation astronauts experience, they also raise concerns about longer-duration missions.
The protein fermentation byproducts have been linked to inflammation, potential kidney damage, and cognitive effects. Although short-term spaceflight poses limited health risks, extended journeys to Mars could allow these harmful compounds to accumulate to dangerous levels. Researchers suggest preventive measures including fiber-enriched diets, probiotics, and medications that stimulate intestinal movement to reduce protein fermentation during long-haul space exploration missions.
Originally reported by Livescience →
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