The Study
Skeletal muscle carnitine loading increases energy expenditure, modulates fuel metabolism gene networks and prevents body fat accumulation in humans
This study shows that when some young men took carnitine with carbs every day, they didn't gain as much fat as others who only took carbs. It also found changes in their muscles and energy use. But because we don't know for sure how people were picked for each group, we can't say for certain that the carnitine caused these changes — it just shows a link.
Analysis score
Maximum 90 for a randomized controlled trial.
Where the score came from
This study looked at whether taking carnitine with sugar every day helps the body burn more fat during light exercise and avoid gaining fat.
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 545 / 100
Quality score
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
Key takeaways
Summary
Based on the study abstract and findings.
- 1Yes, avoiding fat gain without changing exercise is meaningful, but the supplement also required high sugar intake, which may not be healthy long-term.
- 2After 12 weeks, the carnitine group burned 6% more energy during light exercise, used more fat for fuel, and didn't gain fat—while the sugar-only group gained 1.8 kg of fat.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
The Journal of Physiology
Year
2013
Authors
F. Stephens, B. Wall, K. Marimuthu, C. Shannon, D. Constantin-Teodosiu, I. MacDonald, P. Greenhaff
Related Content
Claims (6)
If young, healthy guys boost their muscle carnitine by 20% with supplements, their muscles might be moving fat into energy factories way more—like four times more at rest.
Taking L-carnitine with carbs for 12 weeks might turn up the activity of 73 genes that help the body burn fuel better — especially those involved in how insulin works and how fats are used — in healthy young guys, compared to just taking carbs.
If healthy young guys take a certain amount of L-carnitine with carbs every day for 12 weeks, they might store more carnitine in their muscles, burn more energy during light exercise, and avoid gaining fat compared to just taking carbs.
If healthy young guys take L-carnitine and carbs for 12 weeks, they might burn 6% more energy during light workouts — mostly by burning more fat, not carbs.
When you do light, steady exercise like walking, your body burns more fat compared to carbs than when you're going harder, like running.
If healthy young guys take L-carnitine with carbs twice a day for 12 weeks, they don’t gain the extra body fat that usually comes from just taking carbs — even though both groups are eating more calories than they need.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.