Being underweight makes your heart and lungs less efficient, so you have less stamina and strength.
See the scientific wording
Underweight status reduces cardiovascular endurance and strength.
Contradicted by evidence
Observational2 moderate-quality studies contradict this claim, though the evidence is not conclusive.
What the research says
2 studies reviewedSupporting (0)
No supporting studies found yet
We'll keep looking as more research is published.
Contradicting (2)
The Relationships Between Weight Status and Physical Fitness Among Chinese Children and Youth
Cross-Sectional StudyHuman2019
The study found that kids who are overweight or obese do worse on fitness tests, but being underweight didn't make them worse. So the claim that being underweight hurts stamina is not supported.
Body mass index and physical fitness in Brazilian adolescents.
Cross-Sectional StudyHuman2019
The study found that being underweight doesn't make you much worse at fitness—it's about the same as normal weight, and both are better than being overweight.
Quality-weighted scoring: we follow the GRADE framework — each study is rated High, Moderate, Low, or Very Low based on study design, methodology rigor, and risk of bias. A single high-quality RCT can outweigh several weaker observational studies.
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Score breakdown, mechanism chain, raw evidence, ideal studies needed & 2 contradicting studies
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