The Study
Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis
This study shows that people with higher levels of carnitine in their blood are more likely to have heart disease, especially if they also have high levels of a gut bacteria byproduct called TMAO. It doesn’t prove that carnitine causes heart disease, but it shows a strong link and a possible reason why.
Analysis score
Maximum 72 for a cohort study.
Where the score came from
When people eat red meat, a substance called L-carnitine gets broken down by certain gut bacteria into a chemical called TMAO, which can cause heart disease. People who eat meat regularly have more of these bacteria and make more TMAO. Vegans and vegetarians don’t make much TMAO from L-carnitine.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 561 / 100
Quality score
Groups of people are followed over time to see who develops an outcome. Strong for identifying risk factors and associations, but cannot prove causation as firmly as RCTs.
Key takeaways
Summary
Based on the study abstract and findings.
- 1Yes, this matters: your gut bacteria may turn a nutrient in red meat into a harmful chemical that increases heart disease risk over time.
- 21.
- 3Meat-eaters made more TMAO than vegans after eating L-carnitine.
- 42.
- 5High L-carnitine and TMAO together meant higher heart disease risk.
- 63.
- 7Mice given L-carnitine had 2x more artery damage — unless their gut bacteria were wiped out.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
Nature medicine
Year
2013
Authors
Robert A. Koeth, Zeneng Wang, B. Levison, J. Buffa, Elin Org, Brendan T Sheehy, Earl B. Britt, Xiaoming Fu, Yuping Wu, Lin Li, Jonathan D. Smith, J. DiDonato, Jun Chen, Hongzhe Li, Gary Wu, James D. Lewis, M. Warrier, J. M. Brown, Ronald M. Krauss, W. Tang, Frederic D. Bushman, A. Lusis, S. L. Hazen
Related Content
Claims (5)
If you eat meat and take L-carnitine, your gut bacteria might turn it into a substance that could clog your arteries. But if you're vegan or vegetarian, your gut bugs don’t do this much, so you’re less likely to make that substance.
If someone has high levels of L-carnitine in their blood, they might be more likely to have heart problems — but only if they also have high levels of another substance called TMAO.
Giving mice a supplement called L-carnitine every day makes artery disease about twice as bad, but if you wipe out their gut bacteria with antibiotics, that effect goes away — meaning the gut bugs are behind the harm.
In mice, certain nutrients and a gut chemical they produce can slow down the body's ability to remove cholesterol — but only if the gut bacteria are active.
The kinds of gut bacteria you have, especially if you eat a lot of meat, might be linked to higher levels of a substance in your blood called TMAO, which could mean your diet over time helps shape which bacteria stick around.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.