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Blood tests reveal why astronauts get constipated in space | ScienceDaily (opens in a new tab)

sciencedaily.com · 2026-09-28

Short answerEvidenceSource

Short answer

Mixed

Mixed.

2 claims go further than the study. 2 other points were not covered by the paper.

  • 2 supported
  • 2 overstated
  • 2 not covered

Checked against the study summary. The full text wasn't available, so some details couldn't be settled either way.

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Follow the evidence trail
1
2

NewsLink checks it

Mixed

Two of six claims overstate the study. Two of six check out. Two claims the study doesn't address.

  • 2 supported
  • 2 overstated
  • 2 not covered
Open claim evidence
3
Then inspect each claim

Evidence layer

Claim by claim

Each claim gets a verdict. Expand it to see the evidence directly below.

6 claims in this story

Showing all 6 claimsChoose a verdict to focus the list.

Claim 1 of 6OverstatedThe article says microgravity probably slows food movement through the intestine, which may help explain constipation in astronauts.View evidenceHide evidence

Why this verdict

The abstract supports only a tentative mechanism: increased protein-fermentation signatures may possibly reflect prolonged intestinal transit time caused by microgravity. The story’s phrasing that microgravity 'probably' slows intestinal movement is stronger than the abstract’s uncertainty, and the constipation explanation is not established in the abstract-level profile as a measured clinical endpoint.

1

Study evidence

The authors interpret the flight-induced changes in circulating metabolites as reflecting increased protein fermentation by the gut microbiota, possibly due to prolonged intestinal transit time caused by microgravity.

“The flight-induced changes in metabolites reflected increased protein fermentation by the gut microbiota, possibly reflecting prolonged intestinal transit time caused by microgravity.”
2

Study evidence

Authors propose that increasing intake of slow-fermented carbohydrates on the ISS could reduce gut microbial protein fermentation observed during spaceflight and thereby might improve gastrointestinal health in astronauts on future long-term missions.

“Increasing the consumption of slow-fermented carbohydrates at ISS to reduce protein fermentation might improve gastrointestinal health in astronauts in future human long-term spaceflights.”
Claim 2 of 6OverstatedThe article says the findings could matter for longer missions to the Moon and Mars, and might also help bedridden patients on Earth who experience constipation.View evidenceHide evidence

Why this verdict

The paper profile supports a speculative implication for future long-term human spaceflight and GI health. But the abstract-level paper profile does not specifically mention Moon or Mars missions, bedridden patients on Earth, or constipation as an application, so the story extends the implication beyond what is documented here.

1

Study evidence

Authors propose that increasing intake of slow-fermented carbohydrates on the ISS could reduce gut microbial protein fermentation observed during spaceflight and thereby might improve gastrointestinal health in astronauts on future long-term missions.

“Increasing the consumption of slow-fermented carbohydrates at ISS to reduce protein fermentation might improve gastrointestinal health in astronauts in future human long-term spaceflights.”
Claim 3 of 6Not coveredThe findings came from an investigation of metabolites in astronauts’ blood using a non-targeted approach, and the article says the samples came from three studies conducted aboard the International Space Station.View evidenceHide evidence

As statedthree studies

Why this verdict

The profile supports longitudinal plasma metabolomics using LC–MS in 52 ISS astronauts and describes broad/untargeted metabolomic profiling. However, the abstract-level profile does not verify the specific statement that samples came from three ISS studies, so that part cannot be confirmed at this evidence depth.

1

Study evidence

Spaceflight altered the circulating plasma metabolome; around 40 circulating compounds were affected.≈40 metabolites

“we characterized the plasma metabolome of astronauts (n = 52) before, during, and after missions on board the International Space Station (ISS) using liquid chromatography coupled with mass spectrometry.”
Claim 4 of 6Not coveredThe journal reference listed is a Nature Communications paper titled 'Longitudinal metabolomics profiles reveal increased gut microbial protein fermentation during Spaceflight' with DOI 10.1038/s41467-026-74979-w.View evidenceHide evidence

Why this verdict

The supplied paper profile does not include the article title, journal issue details, or DOI as verifiable metadata, so the bibliographic reference cannot be confirmed from the abstract-level profile provided.

Claim 5 of 6SupportedScientists analyzed blood samples from 52 astronauts who spent months aboard the International Space Station and found signs that the digestive system begins changing relatively soon after astronauts leave Earth.View evidenceHide evidence

As stated52 astronauts

Why this verdict

The abstract-level profile supports the core claim: plasma samples from n=52 ISS astronauts were profiled before, during, and after missions, and metabolite changes were observed shortly after launch. Interpreting these as signs of digestive/GI-related change is consistent with the paper’s protein-fermentation interpretation, though the profile does not give detailed mission-duration wording beyond ISS missions.

1

Study evidence

Spaceflight altered the circulating plasma metabolome; around 40 circulating compounds were affected.≈40 metabolites

“we characterized the plasma metabolome of astronauts (n = 52) before, during, and after missions on board the International Space Station (ISS) using liquid chromatography coupled with mass spectrometry.”
2

Study evidence

The authors interpret the flight-induced changes in circulating metabolites as reflecting increased protein fermentation by the gut microbiota, possibly due to prolonged intestinal transit time caused by microgravity.

“The flight-induced changes in metabolites reflected increased protein fermentation by the gut microbiota, possibly reflecting prolonged intestinal transit time caused by microgravity.”
Claim 6 of 6SupportedThe researchers reported that gut bacteria begin to ferment protein to a greater extent than usual within weeks after astronauts arrive in space, and that the change continues until they are back on Earth.View evidenceHide evidence

As statedwithin weeks

Why this verdict

The paper profile says flight-induced metabolite changes were interpreted as reflecting increased gut microbial protein fermentation, were observed shortly after launch, and subsided within days after landing. The story’s wording is broadly consistent, provided it is understood as an indirect metabolomics-based interpretation rather than a direct measurement of bacterial fermentation activity.

1

Study evidence

Spaceflight altered the circulating plasma metabolome; around 40 circulating compounds were affected.≈40 metabolites

“we characterized the plasma metabolome of astronauts (n = 52) before, during, and after missions on board the International Space Station (ISS) using liquid chromatography coupled with mass spectrometry.”
2

Study evidence

The authors interpret the flight-induced changes in circulating metabolites as reflecting increased protein fermentation by the gut microbiota, possibly due to prolonged intestinal transit time caused by microgravity.

“The flight-induced changes in metabolites reflected increased protein fermentation by the gut microbiota, possibly reflecting prolonged intestinal transit time caused by microgravity.”
Then look for missing context

Context layer

What the story left out

Important study details the story did not include.

  • Diet-related metabolite changes related to caffeine, fish, and fats affected fewer than one third of spaceflight-responsive metabolites.

    The paper treats diet-related signals as a secondary confounder/modifier analysis. The story’s caveats mention interpretive difficulty and individual metabolic variation but do not report the specific diet-related finding.

    From secondary/stratified analyses within a longitudinal observational cohort

  • The authors suggest increasing slow-fermented carbohydrates on the ISS as a possible countermeasure to reduce protein fermentation and improve GI health in future long-term missions.

    The story discusses possible relevance to long missions and other constipation contexts, but it does not reflect the paper’s specific proposed countermeasure involving slow-fermented carbohydrates.

    From narrative inference / recommendation

  • The abstract does not establish clinical GI outcomes such as constipation, nor does it directly measure gut transit time or gut fermentation products.

    This is an interpretation-changing limitation for claims about constipation or slowed intestinal transit. The story mentions uncertainty about mechanism, but it still presents constipation implications without clearly stating that constipation and transit time were not established as measured outcomes in the abstract-level profile.

    From in silico; narrative inference / recommendation

4 things the story did carry across
  • Longitudinal plasma metabolomics in 52 astronauts sampled before, during, and after ISS missions using LC–MS.
  • Spaceflight affected about 40 circulating compounds, with changes observed shortly after launch and subsiding within days after landing.
  • The increased gut microbial protein fermentation conclusion is an interpretation of plasma metabolite patterns, not a direct demonstration of microbial activity or causality.
  • Prolonged intestinal transit in microgravity is presented by the paper as a possible mechanism, not a proven cause.
Then read the study layer

Study layer

Study at a glance

Scan the study first. Expand only the parts you want to inspect.

Pieces of work

4

Evidence read

study summary

Lead result

human in vivo

1Lead resulthuman in vivoCharacterize how spaceflight alters the circulating plasma metabolome over time (before, during, after ISS missions) in astronauts.longitudinal repeated-measures observational studyExpand

In plain English

Longitudinal repeated-measures plasma metabolomics (LC–MS) in n=52 astronauts sampled before, during, and after ISS missions to identify circulating metabolites whose levels change with spaceflight and characterize their temporal dynamics.

Key findings

  • Spaceflight altered the circulating plasma metabolome; around 40 circulating compounds were affected.≈40 metabolites
  • Metabolic changes appeared shortly after launch and largely subsided within a few days after landing.
“we characterized the plasma metabolome of astronauts (n = 52) before, during, and after missions on board the International Space Station (ISS) using liquid chromatography coupled with mass spectrometry.”
What this piece can’t prove
  • Summary and findings are based on the abstract; the abstract does not provide detailed methods, full metabolite identities, quantitative effect sizes, statistical model specifications, or p/q-values.
  • Abstract does not describe controls for dietary intake, medication use, or other potential confounders in detail.

2 further details could not be confirmed from the summary.

2in silicoInterpret flight-associated metabolite shifts as consistent with increased gut microbial protein fermentation (potentially reflecting prolonged intestinal transit time in microgravity).Expand

In plain English

Authors interpret the flight-associated shifts in the plasma metabolome as consistent with increased gut microbial protein fermentation, and propose this could reflect prolonged intestinal transit time in microgravity. The abstract frames this as an interpretive link from the set of metabolites altered during ISS missions to a microbial fermentation process rather than a direct experimental demonstration of microbial activity.

Key findings

  • The authors interpret the flight-induced changes in circulating metabolites as reflecting increased protein fermentation by the gut microbiota, possibly due to prolonged intestinal transit time caused by microgravity.
“The flight-induced changes in metabolites reflected increased protein fermentation by the gut microbiota, possibly reflecting prolonged intestinal transit time caused by microgravity.”
What this piece can’t prove
  • Interpretation is associative; plasma metabolite patterns do not by themselves establish microbial metabolic activity or causality.

2 further details could not be confirmed from the summary.

3human in vivoAssess potential modifiers/confounders and heterogeneity of the metabolomic response (diet-related signals; sex-specific differences).secondary/stratified analyses within a longitudinal observational cohortExpand

In plain English

Within a longitudinal plasma metabolomics study of astronauts (n = 52), the authors report that minor diet-related signals (attributed to caffeine, fish, and some fats) accounted for fewer than one third of metabolites that responded to spaceflight, and that no major sex-specific differences in metabolic response were observed. The abstract provides no statistical detail, diet measurement description, or power information for subgroup analyses.

Key findings

  • Minor diet-related metabolite changes related to intakes of caffeine, fish, and some fats were observed and accounted for fewer than one third of metabolites that responded to spaceflight.
  • No major sex-specific differences in metabolism were observed.
“Minor diet-related changes related to intakes of caffeine, fish, and some fats were also observed but affected less than one third of all metabolites responding to spaceflight.”
What this piece can’t prove
  • Dietary intake ascertainment and timing relative to metabolite sampling are not described, limiting assessment of confounding or exposure measurement error.
  • Power and sample size considerations for subgroup/interaction testing (sex-specific analyses) are not reported, limiting interpretation of null findings.

3 further details could not be confirmed from the summary.

4otherTranslate findings into a practical countermeasure suggestion (increase slow-fermented carbohydrates to reduce protein fermentation and support GI health).narrative inference / recommendationExpand

In plain English

The paper authors recommend increasing consumption of slow-fermented carbohydrates aboard the ISS as a countermeasure to reduce gut microbial protein fermentation observed during spaceflight, with the goal of improving gastrointestinal (GI) health in future long-term missions. This recommendation is presented as an implication drawn from longitudinal plasma metabolomics showing signatures consistent with increased microbial protein fermentation during flight.

Key findings

  • Authors propose that increasing intake of slow-fermented carbohydrates on the ISS could reduce gut microbial protein fermentation observed during spaceflight and thereby might improve gastrointestinal health in astronauts on future long-term missions.
“Increasing the consumption of slow-fermented carbohydrates at ISS to reduce protein fermentation might improve gastrointestinal health in astronauts in future human long-term spaceflights.”
What this piece can’t prove
  • The abstract presents the countermeasure as an implication; no interventional or controlled dietary trial testing increased slow-fermented carbohydrates is reported.
  • Causal linkage between increased protein fermentation signatures and adverse GI health outcomes is not established in this study.
  • Observations come from a cohort of 52 astronauts sampled longitudinally; generalizability to all mission profiles and longer-duration flights is uncertain.
  • Metabolomics-derived interpretation of microbial protein fermentation is indirect; the study does not report direct measures of gut transit time, microbial fermentation end-products in the gut, or clinical GI endpoints.
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