L-carnitine is a nutrient and weight-loss supplement.
Some evidence suggests that supplementing with L-carnitine may promote weight loss. However, studies have provided mixed and inconclusive results.
For this reason, a group of Iranian researchers combined the results of several L-carnitine trials in a meta-analysis.
Here is a summary of their findings.
L-carnitine is a nutrient found in high amounts in meat.
It has essential functions in the body and is involved with fatty acid oxidation (fat burning) and glucose metabolism.
Yet, some researchers believe dietary carnitine intake to be important, and evidence suggests it may promote weight loss by increasing calorie expenditure.
This was a systematic review and meta-analysis of studies examining the effect of L-carnitine on weight loss.
This was a systematic review and meta-analysis of randomized controlled trials testing the effects of L-carnitine on weight loss.
It was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines (1).
Using electronic databases, the researchers searched for all relevant articles. Nine studies, which recruited a total of 911 participants, were selected based on quality criteria.
In all of the studies, the participants supplemented with L-carnitine for at least one month.
Bottom Line: This was a systematic review and meta-analysis of randomized controlled trials examining the effects of L-carnitine on weight loss.
The Selected Studies
Nine studies were selected based on pre-specified criteria. Below are summaries of some of the included studies.
Coelho Cd, et al. The supplementation of L-carnitine does not promote alterations in the resting metabolic rate and in the use of energetic substrates in physically active individuals. Arquivos Brasileiros de Endocrinologia e Metabologia, 2010.
11 physically-active Brazilians supplemented with 1.8 grams of L-carnitine per day for one month. Carnitine supplementation did not affect body composition or calorie intake, compared to a placebo.
Derosa G, et al. The effect of L-carnitine on plasma lipoprotein(a) levels in hypercholesterolemic patients with type 2 diabetes mellitus. Clinical Therapeutics, 2003.
46 diabetic patients supplemented with 2 grams of L-carnitine per day for 3 months. Supplementing with L-carnitine did not cause a greater decrease in body mass index (BMI), compared to a placebo.
Derosa G, et al. Comparison between orlistat plus l-carnitine and orlistat alone on inflammation parameters in obese diabetic patients. Fundamental and Clinical Pharmacology, 2011.
258 diabetic patients were randomly assigned to supplement with 120 mg of orlistat three times per day, or the same amount of orlistat plus 2 grams of L-carnitine once per day, for one year.
Those who supplemented with orlistat and L-carnitine lost significantly more weight, compared to those who only took orlistat.
254 diabetic patients were randomly assigned to receive either 10 mg of sibutramine plus 2 grams of carnitine, or sibutramine alone, every day for one year. Supplementing with L-carnitine led to significantly greater weight loss.
Elmslie JL, et al. Carnitine does not improve weight loss outcomes in valproate-treated bipolar patients consuming an energy-restricted, low-fat diet. Bipolar Disorders, 2006.
30 patients with bipolar disorder supplemented with 33 mg of L-carnitine per pound (15 mg per kilogram) of body weight daily for 26 weeks while following a moderately calorie-reduced diet.
Supplementing with L-carnitine did not significantly affect weight loss, compared to a placebo.
Pistone G, et al. Levocarnitine administration in elderly subjects with rapid muscle fatigue: effect on body composition, lipid profile and fatigue. Drugs & Aging, 2003.
42 healthy older people supplemented with 4 grams of L-carnitine every day for one month while following an exercise program.
Those who supplemented with L-carnitine lost significantly more fat mass and gained greater muscle mass, compared to a placebo.
Rafraf M, et al. Effect of L-carnitine supplementation in comparison with moderate aerobic training on serum inflammatory parameters in healthy obese women. The Journal of Sports Medicine and Physical Fitness, 2015.
22 obese women from Iran supplemented with 2 grams of L-carnitine per day for two months. Half of them followed an aerobic training program.
Supplementing with L-carnitine alone, or in combination with aerobic training, did not significantly affect body weight.
Villani RG, et al. L-Carnitine supplementation combined with aerobic training does not promote weight loss in moderately obese women. International Journal of Sport Nutrition and Exercise Metabolism, 2000.
18 overweight Australian women supplemented with 4 grams of L-carnitine for two months. They also walked for 30 minutes four days per week. Supplementing with L-carnitine did not affect total body mass or fat mass.
Finding: L-Carnitine May Cause Weight Loss
Supplementing with L-carnitine led to a 1.33 kg greater weight loss, on average, compared to a placebo.
L-carnitine supplementation led to significant weight loss in diabetic and non-diabetic individuals, as well as obese and normal-weight people.
Additionally, the analysis indicated that the weight loss effects of L-carnitine are strongest in the beginning but decrease over time.
However, the relevance of these findings is unclear because the included studies varied widely in their design.
Bottom Line: This meta-analysis concluded that supplementing with L-carnitine may cause slight weight loss.
The main limitation of this meta-analysis was its study selection.
The included studies differed in their methods and not all were weight-loss trials. This makes interpreting the findings difficult.
The meta-analysis itself didn’t appear to have any methodological limitations, but the paper lacked detail, clarity and contained some incorrect references.
Summary and Real-Life Application
In short, this meta-analysis of randomized controlled trials suggests that supplementing with L-carnitine for more than a month may promote modest weight loss.
However, the evidence is inconclusive and limited overall. More high-quality studies are needed.