52 astronauts left Earth for months in orbit, and within weeks their gut bacteria changed how they processed food, revealing why spaceflight can trigger constipation and potentially affect brain health

Constipation in space is more than an uncomfortable side effect. Astronauts often face it during long missions, but scientists have not fully understood why. Now, blood tests from 52 astronauts reveal a possible clue. Their gut bacteria began fermenting more protein within weeks of reaching the International Space Station. The finding links microgravity, slower intestinal movement and gut microbiome changes, offering new clues for future Moon and Mars missions.