Study Finds Why Astronauts Struggle With Constipation in Space

A study published in the journal Nature Communications has traced why astronauts commonly struggle with constipation in space. Researchers analyzed 488 blood samples collected from 52 astronauts, both while they were aboard the International Space Station and after they returned to Earth. The astronauts had spent between two and nine months in space, and the samples were examined for changes in molecules linked to the body, gut food and gut microbes.

The researchers found that in microgravity, gut motility — the movement that pushes food through the digestive system — becomes much slower. Normally, gut microbes rely mainly on fiber and carbohydrates to produce energy from food; in space, the study found, they instead rely far more heavily on protein. In total, about 40 components in the astronauts' bodies changed, most of them linked to gut microbes breaking down protein for energy.

Because digestion and the separation of waste slow down in microgravity, stool forms more slowly, and astronauts pass it less often. Over long stretches in space, the researchers found, this can affect health and lead to a build-up of unwanted toxins — a concern for future missions that could keep astronauts in space for years at a time.

The changes began within a few days of launch, the study found, and reversed within a few days of the astronauts landing back on Earth. Adjusting astronauts' diets could help reduce the changes to some extent, but a lasting solution will require further research.