Scientists may finally know why astronauts face constipation in space — and how to prevent it during missions to the Moon and Mars

In order to find it out, researchers analyzed blood samples of 52 astronauts who spent 2-9 months in space.

One of the known side effects of space flights is constipation, but scientists may finally know why it occurs. By working with NASA, researchers from the University of Copenhagen followed the link between microgravity and altered gut bacteria, which may lead to intestinal issues. According to the study published in the journal Nature Communications , findings may help prevent constipation and maintain overall health of astronauts during long-term missions beyond our planet.

The study analyzed blood samples of 52 different astronauts who spent between 2 and 9 months in space (International Space Station) between 2006 and 2018. By observing the samples, the researchers suggest that low gravity levels slow down the digestion process and ferment proteins at a higher rate than usual. The phenomenon of protein fermentation occurs when there is an excess of protein in the intestines, beyond what is needed for energy. This usually happens when a person’s diet lacks fiber, which is necessary for peristalsis, or the peristaltic waves of the esophagus.

“The lack of gravity in space probably reduces the peristaltic movements in the intestines, and this may partly explain why protein fermentation was increased. This could also be the reason why astronauts faced constipation on the ISS,” Henrik Roager, one of the researchers and associate professor at the Department of Nutrition, Exercise and Sports explains. According to him, scientists also noted that protein fermentation was particularly intense several weeks after leaving the spaceship and before returning to Earth.

“Due to the nature of the study, we were able to analyze blood samples from 52 different astronauts who flew several missions between 2006 and 2018. That’s quite unique, since studies usually follow one group of people and their health status throughout the course of an experiment. However, in this case, we managed to see exactly how protein fermentation responded to a space flight due to the variety of samples,” joint first author and assistant professor Jan Stanstrup added.

The authors noted that in 488 plasma samples they reviewed, they found numerous metabolites changed due to space travel. These molecules circulate in our bodies and indicate the state of our organs, nutrition, and other vital functions, such as intestinal activity. By analyzing them, scientists can determine how a person’s health is affected by various external factors, such as a low-gravity environment. Lars Ove Dragsted, senior author of the study and professor at the Department of Nutrition, Exercise and Sports, notes that protein fermentation is usually associated with impaired kidney function and may lead to mood disorders and a decrease in attention span.

“To maintain a healthy gut microbiome and prevent constipation, astronauts need to adjust their diet to include more fiber or receive special treatment which will reduce the time food spends in the intestines. This way, protein fermentation will be minimized and the negative effects of a low-gravity environment on the digestive system will be prevented,” Henrik Roager suggests. According to him, these findings may also be useful for patients with similar conditions on Earth since protein fermentation is often observed among people with diet-related diseases, although to a lesser extent than among astronauts.