A University of Copenhagen study published in Nature Communications, conducted in collaboration with NASA, reveals why constipation is a well-known problem for astronauts in space. By examining blood samples from 52 astronauts who have participated in months long missions to the International Space Station, researchers identified gastrointestinal changes that occur shortly after the astronauts leave Earth and gravity behind.
The researchers discovered that altered gut motility prompts bacteria to ferment dietary proteins rather than depleted fibers. This international research effort leverages longitudinal metabolic data from multiple spaceflight missions, shedding light on the links between microgravity, gut microbial activity, and systemic metabolic function.
In Plain English: The Clinical Takeaway
- Microgravity and Digestion: The lack of gravity in space probably causes food to move more slowly through the intestine.
- The Protein Fermentation Shift: With dietary fiber depleted and food lingering longer in the digestive tract, gut microbes start breaking down protein instead.
- Systemic Signalling: These protein-derived metabolites enter the bloodstream and can affect the brain through the gut-brain axis, potentially impacting mood or reduced ability to focus.
Metabolic Shifts and the Gut-Brain Axis in Space
To decode how spaceflight alters human metabolism, the investigative team analyzed blood metabolites—small molecules in the circulation—from 52 astronauts who completed multi-month deployments aboard the International Space Station. The findings indicate that within weeks of leaving Earth, microbial populations in the gut shift their metabolic focus. As joint first author and associate professor at the Department of Nutrition, Exercise and Sports Giorgia La Barbera noted, blood profiles show clear signs that gut bacteria ferment protein to a greater extent than usual, persisting until the return to terrestrial gravity.
Coauthor Henrik Roager detailed the mechanical background behind this alteration: “The lack of gravity in space probably causes food to move more slowly through the intestine, and this fits with the fact that we are seeing signs of increased protein fermentation. This may also help explain constipation in astronauts.” According to senior author and professor at the Department of Nutrition, Exercise and Sports Lars Ove Dragsted, products of protein fermentation are often associated with negative health consequences, such as kidney damage, potential effects on mood or reduced ability to focus, among others.
Overcoming Research Variability Through Longitudinal Data
Human metabolism studies are frequently hampered by high inter-individual variability, making clinical interpretation complex. However, the unique cohort of 52 astronauts spanning numerous missions across multiple years provided a dataset that helped to reduce that variability. Joint first author and assistant professor Jan Stanstrup emphasized the strength of this approach, highlighting how consistency across diverse flight missions elevated confidence in the metabolic findings.
| Research Parameter | Clinical Detail |
|---|---|
| Cohort Size | 52 astronauts across multi-month International Space Station missions |
| Primary Specimen | Blood metabolites |
| Key Physiological Marker | Increased protein fermentation resulting from slowed transit time |
| Primary Publication | Nature Communications, in collaboration with NASA and the University of Copenhagen |
Translational Implications for Terrestrial Healthcare
Beyond orbital applications, these insights carry relevance for terrestrial populations, particularly bedridden patients. They also experience constipation and likely also have increased protein fermentation that may aggravate health conditions. Clinicians can leverage this knowledge to help these patients.
As space agencies plan extended exploration missions to the Moon and beyond, the study authors point out that these current findings could prove significant. To offset the adverse impacts of space missions on gastrointestinal health, investigators propose potential remedies including prebiotic supplements, boosted dietary fiber intake, or alternative interventions that stimulate peristalsis and accelerate bowel transit times.
References
- University of Copenhagen. Why constipation is common in astronauts.
- Nature Communications. Research conducted in collaboration with NASA.
