Does l-carnitine result in weight loss?

Posted 13 September 2016

A recent review (October 2016) in Obesity Reviews of the use of l-carnitine in weight-loss concludes in the summary (abstract) that “[W]e conclude that receiving the carnitine resulted in weight loss”. [1] Without reading the full article, this study may be used by supplement sellers to support their claims that this ingredient is effective for weight-loss.

This study was a systematic review and meta-analysis of randomized controlled trials, which examined the effect of the carnitine on adult weight loss. However, note: Nine studies of a total of 911 of adequate methodological quality were included in the review. The authors write: “Results from meta-analysis of eligible trials revealed that subjects who received carnitine lost significantly more weight (MD: −1.33 kg; 95% CI: −2.09 to −0.57) and showed a decrease in body mass index (MD: −0.47 kg m−2; 95% CI: −0.88 to −0.05) compared with the control group.” [1]

Wow! Carnitine works! Not so fast.

But, as often is the case, researchers do not differentiate in the abstract, or study, the difference between clinically significant versus statistical difference. In other words, if I take 100 women and give them l-carnitine, and they lose in 1 year 200 grams versus 1 gram for 100 women taking a placebo, that would be statistically significant (200 gms vs 1 gm). But clinically irrelevant.

So what does the study actually conclude? That including 9 of a total of 911 studies, that on average subjects given l-carnitine lost 1.33 kg more than those taking placebo. However: the range of weight-loss, i.e., from the 9 studies varied from one showing the highest average weight-loss of 2.09 Kg to one showing the lowest average weight-loss of 0.57 kg. The carnitine dosage varied from 1.8 g per day to 4 g per day in the trials.

The study that found that on average that 0.57 kg was lost, is titled “L-carnitine supplementation combined with aerobic training does not promote weight loss in moderately obese women”.[2] In other words, the value of 1.33 kg is an average of the average of each of the 9 studies, the lowest being 0.57 kg and concluding that l-carnitine is ineffective.

The study showing the best weight-loss evaluated 60 obese premenopausal women with type II diabetes who were divided into two groups, case and control. For about 8 weeks, the case group received L-carnitine supplement (2 grams daily) combined with the low calorie diet, and the control group received placebo plus low-calorie diet. The average weight-loss for the case group vs control group was 1.99 kg. The case group weighed 83.8 ± 8.21 before the intervention which dropped to 79.14 ± 7.65 and the control group, from 84.23 ± 7.8 to 81.56 ± 7.2. But what we are unable to evaluate from the study, is whether ALL of the case group lost effective weight, some may have lost nothing: i.e., if three lost 4 kg and three lost zero grams, the average weight-loss will be 2 kg ± 2.

One has to purchase the article to be able to read the nuances. In the discussion is this point: “Although the analysis indicated that dosage of carnitine had positive, but not significant, impact on weight change, insufficient power of analysis precluded us to have any recommendation regarding the best dosage of the carnitine”.

So in conclusion, one has to be very, very careful how studies are interpreted – even systematic review and meta-analysis of randomized controlled trials.

[1] M. Pooyandjoo, M. Nouhi, S. Shab-Bidar, K. Djafarian and A. Olyaeemanesh. The effect of (L-)carnitine on weight loss in adults: a systematic review and meta-analysis of randomized controlled trials. Obesity Reviews 2016;17 (10):970–976.

[2] Villani RG, Gannon J, Self M, Rich PA. L-carnitine supplementation combined with aerobic training does not promote weight loss in moderately obese women. Int J Sport Nutr Exerc Metab 2000; 10: 199–207.

[3] Barzegar A, Alipour B, Panahi F, Karamzad N. Effect of L-carnitine supplementation on serum adipokines (leptin and visfatin) levels in obese type II diabetes mellitus women with hypocaloric diet. Life Sci J 2013; 10: 359–65.

M. Pooyandjoo, M. Nouhi, S. Shab-Bidar, K. Djafarian and A. Olyaeemanesh. The effect of (L-)carnitine on weight loss in adults: a systematic review and meta-analysis of randomized controlled trials. Obesity Reviews 2016;17 (10):970–976.

Summary

This study provides a systematic review and meta-analysis of randomized controlled trials, which have examined the effect of the carnitine on adult weight loss. Relevant studies were identified by systematic search of PubMed, Embase, Cochrane Central Register of Controlled Trials and reference lists of relevant marker studies. Nine studies (total n = 911) of adequate methodological quality were included in the review. Trials with mean difference (MD) of 95% confidence interval (CI) were pooled using random effect model. Results from meta-analysis of eligible trials revealed that subjects who received carnitine lost significantly more weight (MD: −1.33 kg; 95% CI: −2.09 to −0.57) and showed a decrease in body mass index (MD: −0.47 kg m−2; 95% CI: −0.88 to −0.05) compared with the control group. The results of meta-regression analysis of duration of consumption revealed that the magnitude of weight loss resulted by carnitine supplementation significantly decreased over time (p = 0.002). We conclude that receiving the carnitine resulted in weight loss. Using multiple-treatments meta-analysis of the drugs and non-pharmacotherapy options seem to be insightful areas for research. © 2016 World Obesity

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