Narrative reviewindependent cross-checkabstract checked I-SOD-116 standard review
A person breathes out about 1 kg of CO2 a day
Review of carbon dioxide removal and recycling in space.
Overview
O'Sullivan C et al.. NPJ Microgravity 2026 · PMID 42120392 · DOI 10.1038/s41526-026-00608-x
Space life-support engineering uses about 1 kg of carbon dioxide per crew member per day as the design value.
Does the study support the specific claim? No · Methodological quality: moderate
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Review CO2 removal in spacecraft.
- How was the study done?
Technical review.
- How many people, animals or samples were studied?
Not applicable.
- What was actually found?
Each person produces about 1 kg of CO2 per day.
- How large was the observed effect?
Not applicable.
- What do the results mean in everyday life?
The body makes hundreds of times more CO2 each day than a can of soda contains.
- What are the study's limitations?
Indirect source.
- What does it say about Elawady's specific claim?
Refutes the CO2 comparison in the claim.
- Do the results apply to Germany and Europe?
Universal.
- What can explicitly not be concluded from this study?
Not a nutrition study.
Scientific in-depth review
1. Full reference
- Authors
- O'Sullivan C et al.
- Journal
- NPJ Microgravity
- Year
- 2026
- Identifier
- PMID 42120392 DOI 10.1038/s41526-026-00608-x
- Verification
- verified – PubMed efetch 2026-10-26 + Crossref 2026-10-26
- Retracted
- no
- Corrections
- none
- Extent checked
- abstract only
- Conflicts of interest and funding
Not stated in abstract record
2. Research question
What technologies remove and recycle CO2 in spacecraft?
3. Study design and population
- Study design
- Narrative review – Narrative technical review
- Population
Not applicable
- Country
International
- Period
2026
- Sample size
Not applicable
- Inclusion and exclusion criteria
Not applicable
4. Methods and endpoints
- Exposure / intervention
Not applicable
- Comparator
Not applicable
- Endpoints
CO2 removal capacity
- Statistical methods
Not applicable
5. Actual results
- Results
Full-text passages (PMC13392110, checked 2026-10-26): a tested method 'was not capable of capturing the target scale of one crew member, i.e., 1 kg per day'; the ISS carbon dioxide removal assembly 'processes over 4 kg/day of CO2 produced by the crew'.
- Absolute risks
not applicable
- Authors' conclusion
Technical review (not health-related).
6. Strengths
- Engineering design value used by space agencies
7. Weaknesses
- Indirect source for human physiology
- Approximate per-person figure
8. Risk of bias
- Orienting tool
- none applicable
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- not assessable
- Rationale
Used only as a source for daily human CO2 output.
9. Assessment of the statistical interpretation
~1 kg/day vs 1.8 g per 300 mL soda: ~550-fold difference (stats/C-SOD-13_co2_budget.py).
10. Relevance to the specific claim
Gives the daily CO2 output of one person (~1 kg/day), showing that one 300 mL soda (~1.8 g) contains about 0.2% of daily metabolic CO2 production.
11. Independent contrary findings
None.
12. Transferability to Germany and Europe
Universal physiology.
13. Overall methodological judgement
Adequate order-of-magnitude source.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | moderate |
| Risk of bias | not assessable |
| Precision of results | moderate |
| Directness | indirect |
| Reproducibility | replicated |
| Consistency with the overall evidence | consistent |
| Regional transferability | high |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
None.
15. Linked fact checks
- Elawady: the harm of soda is the carbonated water itself, not the sugar or sweetener; one 300 ml Pepsi delivers more carbon dioxide than the body produces in a whole day, and colas contain sodium bicarbonate that neutralises stomach acid and increases reflux. – Studies contradicting or limiting the claim