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A University of Copenhagen study conducted with NASA found blood metabolite patterns in 52 astronauts that suggest gut bacteria shifted toward protein fermentation during months aboard the International Space Station. Researchers say slower movement of food through the intestines in microgravity may help explain constipation, but the study does not establish that as the cause.
Blood samples from 52 astronauts who spent months aboard the International Space Station show signs that gut bacteria shifted toward protein fermentation within weeks of arriving in space, according to research from the University of Copenhagen conducted with NASA. The researchers say the pattern may help explain constipation during spaceflight, though it does not prove that microgravity or the bacterial changes cause the condition.
The team examined metabolites, small molecules circulating in the blood that can offer clues about processes in the body, including digestion and metabolism. The samples showed a recurring pattern that researchers interpreted as increased fermentation of protein by gut bacteria. Joint first author Giorgia La Barbera said the changes appeared within weeks of arrival in space and continued until astronauts returned to Earth.
In the researchers’ explanation, protein fermentation can increase when intestinal bacteria have used available dietary fiber and begin breaking down protein instead. The process also occurs on Earth. The team suspects that food may move more slowly through the intestine in microgravity, giving bacteria more time to ferment protein. Co-author Henrik Roager said this possibility fits the blood findings and may help explain constipation, but the supplied report does not establish a direct cause-and-effect relationship.
The study drew on samples from astronauts on different missions over several years. Joint first author Jan Stanstrup said the range of astronauts was unusual for this kind of research, in which differences in people’s metabolism can make patterns harder to interpret. The researchers reported that their method showed a consistent signal across the sample group. The supplied account does not give further details about the sampling schedule or the size of the changes.
Gut Health on Longer Missions
The findings could inform planning for missions that keep crews away from Earth for longer periods, including future journeys to the Moon and Mars. Constipation and changes in digestion can affect daily comfort and crew routines; a gut change that persists throughout a mission could become more relevant as time in space increases. The research points to a possible biological process that mission health studies may need to track alongside symptoms.
Senior author Lars Ove Dragsted said some products of protein fermentation have been associated with potential health concerns, including kidney damage and possible effects on mood or ability to focus. Those are associations cited by the researchers, not outcomes shown in this astronaut study. The report does not say that the astronauts experienced these effects. The blood pattern is a reason to investigate further, rather than evidence that spaceflight caused those harms.
The work may also be relevant to people on Earth who spend extended periods confined to bed and experience constipation. The researchers suggest that slowed intestinal movement could produce similar fermentation changes, but whether that happens in bedridden patients remains to be established. The study offers a possible line of inquiry, not a tested treatment for either astronauts or patients.
How Spaceflight May Change Digestion
Constipation is a familiar issue in spaceflight, but the precise reasons have not been fully understood. The Copenhagen and NASA collaboration approached the question by looking for metabolic signals in blood, rather than relying only on reported symptoms. Metabolites can reflect activity in the gut and other bodily processes, although they do not by themselves identify the cause of a change.
Protein fermentation happens when gut bacteria break down protein and produce metabolites. The researchers describe it as more likely when fiber has been used and material remains in the intestines for longer. Peristalsis—the coordinated contractions that move food and waste through the digestive tract—helps determine how quickly that material passes. The team proposes that microgravity may slow this movement, but the report presents that as a possible mechanism.
The researchers say the findings could guide future work on ways to support gut movement and fiber availability during spaceflight. They mention increased dietary fiber, prebiotics, and other treatments that promote peristalsis as potential approaches. The report does not establish that any of these measures prevent constipation or reduce fermentation in astronauts.
““We see changes in astronauts’ blood samples that indicate that the gut bacteria begin to ferment protein to a greater extent than usual within weeks after the astronauts arrive in space, and this change continues until they are back on Earth.””
— Giorgia La Barbera, joint first author and associate professor at the University of Copenhagen
Cause and Health Effects Still Open
The blood findings indicate a pattern consistent with increased protein fermentation, but the reported evidence does not show that the process directly caused constipation. The researchers’ explanation—that microgravity slows intestinal movement and gives bacteria more time to ferment protein—is a proposed mechanism. The account does not report a direct measurement linking transit time, fermentation and constipation symptoms in each astronaut.
It also remains unclear how large the metabolic changes were, whether they differed by mission or diet, and whether they led to measurable health effects. The researchers cite possible risks associated with fermentation products, but the supplied report does not say the study demonstrated kidney, mood or concentration problems in the astronauts. Whether similar changes occur in bedridden patients is also unresolved.
Testing Ways to Support Gut Transit
The researchers say the findings can inform potential countermeasures for longer missions. Approaches they identify include more dietary fiber, prebiotics, and other treatments intended to promote peristalsis and shorten gut transit time. These are research possibilities, not established recommendations for astronauts. The report does not specify when or how such measures will be tested.
Further work would need to determine whether changing diet or gut transit affects the blood metabolite pattern and constipation during spaceflight. As agencies plan longer journeys, researchers will need to establish which changes are consistent across crews, how they relate to symptoms, and whether any intervention improves digestive health without causing other problems. The study supplies a possible biological lead; the next practical milestone is testing the proposed links and responses.
Key Questions
What did the blood tests show?
Samples from 52 astronauts showed metabolite patterns that researchers said indicate increased protein fermentation by gut bacteria during spaceflight. The changes appeared within weeks of arrival and continued until return to Earth, according to the study’s first author.
Does the study prove why astronauts get constipated?
No. The researchers propose that microgravity may slow the movement of food through the intestines, allowing more protein fermentation. The reported findings suggest a possible explanation but do not establish that this process causes constipation.
What is protein fermentation?
It is a process in which gut bacteria break down protein and produce metabolites. The researchers say it may become more likely when available fiber has been used and material remains in the intestines longer.
Could the findings help people on Earth?
Researchers say the work may be relevant to people confined to bed who experience constipation. Whether they have the same fermentation changes has not been established in the reported study.
What might researchers try next?
The team identifies dietary fiber, prebiotics and other approaches intended to support intestinal movement as possibilities for future investigation. The report does not show that these measures have been tested as effective countermeasures for astronauts.
Source: rss
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