# NASA-University of Copenhagen astronaut gut health study > Live situation record from CLSTR: https://clstr.news/situations/nasa-university-of-copenhagen-astronaut-gut-health-study > Updated: 2026-08-21T16:05:52.000Z. Sources: 6. Developments: 2. A collaborative study by NASA and the University of Copenhagen has identified biological mechanisms behind frequent constipation and gastrointestinal issues among astronauts. By analyzing blood metabolites from 52 astronauts who served on the International Space Station between 2006 and 2018, researchers determined that microgravity is the primary driver of these changes. The research, published in Nature Communications, indicates that microgravity slows the transit of food through the digestive tract. This delay causes a shift in the gut microbiome; once dietary fiber and carbohydrates are exhausted, gut bacteria switch to fermenting proteins for energy. This process produces metabolites such as ammonia and hydrogen sulfide. While dietary factors like caffeine or fat intake contribute to metabolic shifts, they account for less than one-third of the observed changes, confirming microgravity as the main cause. ## Timeline ### 2026-08-21: NASA and researchers identify cause of astronaut constipation A NASA-funded study reveals that microgravity causes food to move slower through the gut, forcing bacteria to ferment protein instead of carbohydrates, leading to constipation in astronauts. 2 sources. https://clstr.news/cluster/nasa-and-researchers-identify-cause-of-astronaut-constipation ### 2026-08-17: NASA and University of Copenhagen study links microgravity to astronaut constipation Researchers from the University of Copenhagen and NASA found that microgravity may cause constipation in astronauts by slowing intestinal movement and increasing protein fermentation by gut bacteria. 4 sources. https://clstr.news/cluster/nasa-and-university-of-copenhagen-study-links-microgravity-to-astronaut-constipation --- Cite as: NASA-University of Copenhagen astronaut gut health study. CLSTR, https://clstr.news/situations/nasa-university-of-copenhagen-astronaut-gut-health-study