Effects of acute versus chronic L-carnitine L-tartrate supplementation on metabolic responses to steady state exercise in males and females.
Level 2 - randomized trial
Randomized, double-blind crossover trial
PubMed 16286670 · doi:10.1123/ijsnem.15.4.386
What was done
Twelve healthy active adults (6 men, 6 women) completed 60 minutes of steady-state exercise at 60% VO2max on three separate occasions under randomized, double-blind crossover conditions. Participants received acute L-carnitine L-tartrate (LCLT), chronic LCLT, or placebo. Diet and exercise were replicated for 2 days before each trial, and substrate oxidation rates along with hematological responses were measured.
What was found
In males, the rate of carbohydrate (CHO) oxidation differed significantly between placebo and chronic trials (P = 0.02) but not between placebo and acute trials (P = 0.70). Total CHO oxidation in males was higher following chronic supplementation versus placebo (mean ± SD: 93.8 ± 17.3 g/hr vs. 78.2 ± 23.3 g/hr). In females, no significant differences were observed in CHO oxidation rate or total CHO oxidation across trials. Neither sex showed effects on fat oxidation or hematological responses.
Why it matters
This study shows that chronic L-carnitine supplementation can shift substrate use toward increased carbohydrate oxidation during steady-state exercise in males, directly challenging common assumptions that carnitine promotes fat oxidation.
Limits
The sample size is very small (n = 12 total, 6 per sex subgroup), limiting statistical power. The abstract does not specify the exact dosages or duration of the chronic supplementation protocol.
Cited by
- supports The scientific evidence supporting carnitine supplementation to increase fatty acid oxidation is weak.