Effects of four weeks L-carnitine L-tartrate ingestion on substrate utilization during prolonged exercise.
Level 2 - randomized trial
Individual randomized crossover trial
PubMed 16521850 · doi:10.1123/ijsnem.15.6.665
What was done
In a randomized, placebo-controlled, double-blind crossover trial, 15 trained males completed two 4-week supplementation periods receiving either 3 g/day L-carnitine L-tartrate (LCLT) or 3 g/day placebo. Participants performed exercise testing at baseline (0 wk) and after 4 weeks (4W), consisting of 90 minutes of steady-state cycling to measure substrate oxidation followed by a 20 km cycling time trial.
What was found
Total carbohydrate and fat oxidation during 90 minutes of steady-state cycling showed no significant changes from week 0 to week 4 within either condition (mean ± SD): - Carbohydrate oxidation: Placebo 99 ± 36 g (0 wk) vs 111 ± 27 g (4W); LCLT 107 ± 33 g (0 wk) vs 112 ± 32 g (4W). - Fat oxidation: Placebo 99 ± 28 g (0 wk) vs 92 ± 21 g (4W); LCLT 94 ± 18 g (0 wk) vs 90 ± 22 g (4W). Subsequent 20 km time trial duration improved significantly after placebo (from 31:29 ± 3:50 to 29:55 ± 2:58 min:s, P < 0.01), but showed no significant change with LCLT (from 31:46 ± 4:06 to 31:19 ± 4:08 min:s).
Why it matters
This study finds no evidence that 4 weeks of oral L-carnitine L-tartrate supplementation enhances fat oxidation or improves endurance performance in trained individuals.
Limits
The study was small (n = 15) and included only trained males, limiting generalizability to untrained individuals or females. The abstract does not report muscle carnitine content or specify the washout duration between crossover periods.
Cited by
- supports The scientific evidence supporting carnitine supplementation to increase fatty acid oxidation is weak.