L-Carnitine
Brief description
L-Carnitine is a non-protein amino acid that is made in the brain, liver, and kidneys. It helps the body turn fat into energy, however, it is thought to have many mechanisms of action and further research is needed to understand them better (see below).
Dietary sources of L-Carnitine include meat, fish, poultry and milk.
Mechanism of action:
L-Carnitine plays a role in the oxidation of fatty acids in skeletal and cardiac muscle by transporting long chained fatty acids in the mitochondria (providing energy).
Can improve cholesterol markers via inhibition of β-hydroxy β-methylglutaryl (HMG)-CoA reductase activity.
Evidence base
Weight loss: A systematic review of 24 trials (n=1520 participants) found supplementation was able to reduce body weight (after subgroup analysis) by 1.53kg and 1.29kg in obese (P=0.01) and overweight (P< 0.001) individuals, respectively.
No weight loss change was observed in normal weight individuals. When combined with a low-calorie diet and exercise, findings were even more significant(1).
Cholesterol: Supplementation of >2g/day was able to significantly reduce: total cholesterol (ES = −1.05 mg/dL, 95% CI: −1.71, −0.39; p = 0.002); triglycerides (ES = −2.51 mg/dL; 95% CI: −3.62, −1.39, p < 0.001;12 meta-analyses); and LDL (bad cholesterol) (ES = −4.81 mg/dL; 95% CI: −6.04, −3.59; p < 0.001;11 meta-analyses). L-Carnitine was also able to increase HDL-C (good cholesterol) (ES = 0.66 mg/dL, 95% CI: 0.20, 1.12, p = 0.005; 11 meta-analyses). All significant findings were with interventions <18weeks(2).
Blood glucose: Findings from multiple systematic reviews demonstrated supplementation of 1000-2000mg/day was able to significantly lower fasting blood glucose HbA1c and insulin levels(3). Findings extended to those overweight and obese, and or diabetic(4).
Recommended serving & duration.
2g/day is suggested in most studies.
Safety & tolerability
Generally reported as safe and well tolerated(5-7).
Nausea and stomach discomfort (at 2g/day dosage) was reported in the meta-analysis of 37 trials(1).
Muscle cramps, diarrhoea, flu-like symptoms, and headache with higher doses (>5g/day)(3).
If in any doubt whether L-carnitine is safe for you to consume, please consult with your local healthcare provider. Particularly, if you are <18 years, pregnant or breastfeeding.
References:
Talenezhad N, Mohammadi M, Ramezani-Jolfaie N, Mozaffari-Khosravi H, Salehi-Abargouei A. Effects of l-carnitine supplementation on weight loss and body composition: A systematic review and meta-analysis of 37 randomized controlled clinical trials with dose-response analysis. Clin Nutr ESPEN. 2020;37:9-23.
Musazadeh V, Alinejad H, Esfahani NK, Kavyani Z, Keramati M, Roshanravan N, et al. The effect of L-carnitine supplementation on lipid profile in adults: an umbrella meta-analysis on interventional meta-analyses. Front Nutr. 2023;10:1214734.
Fathizadeh H, Milajerdi A, Reiner Ž, Kolahdooz F, Asemi Z. The effects of L-carnitine supplementation on glycemic control: a systematic review and meta-analysis of randomized controlled trials. Excli j. 2019;18:631-43.
Zamani M, Pahlavani N, Nikbaf-Shandiz M, Rasaei N, Ghaffarian-Ensaf R, Asbaghi O, et al. The effects of L-carnitine supplementation on glycemic markers in adults: A systematic review and dose-response meta-analysis. Front Nutr. 2022;9:1082097.
Liu A, Cai Y, Yuan Y, Liu M, Zhang Z, Xu Y, et al. Efficacy and safety of carnitine supplementation on NAFLD: a systematic review and meta-analysis. Syst Rev. 2023;12(1):74.
Brass EP, Koster D, Hiatt WR, Amato A. A systematic review and meta-analysis of propionyl-L-carnitine effects on exercise performance in patients with claudication. Vasc Med. 2013;18(1):3-12.
Kamoen V, Vander Stichele R, Campens L, De Bacquer D, Van Bortel L, de Backer TL. Propionyl-L-carnitine for intermittent claudication. Cochrane Database Syst Rev. 2021;12(12):Cd010117.
