Many things change in space, including how the intestines function. Constipation is a known side effect of space travel, but until now, little has been known about why it happens.

Constipation is a familiar problem for astronauts, but the biological reason it develops during spaceflight has remained uncertain.

Researchers from the University of Copenhagen working with NASA have now found evidence of what may change in the digestive system when gravity disappears. They analyzed blood samples from 52 astronauts who spent months aboard the International Space Station and detected gastrointestinal changes that appeared within weeks of leaving Earth.