Supplements · 5 min read ·

Fat burners: do they work?

Caffeine, green tea, carnitine, garcinia… They promise to "burn" fat. What summaries of studies show — and why a fat burner may contain something that is not on the label.

In a nutshell

1What the summaries say

Strong evidence 315 studies A systematic review of 315 randomised trials of 14 supplements and alternative therapies for weight loss: only 52 studies had a low risk of bias and only 16 of them found a significant difference in weight (0.3–4.9 kg). According to the authors, there is little high-quality evidence of efficacy.1

2Individual ingredients

Strong evidence −0.04 kg Green tea: in six studies outside Japan, people taking green tea lost only 0.04 kg more than with placebo — practically the same. The eight Japanese studies differed so much that the authors could not combine them; the difference in them ranged from 0.2 to 3.5 kg in favour of green tea. Overall, the effect was small and not statistically significant.2
Moderate evidence −1.3 kg Carnitine: in 9 studies with 911 people, those taking carnitine lost 1.33 kg more than with placebo. But the longer they took it, the smaller the difference became.3
Moderate evidence −0.5 to −0.9 kg Garcinia, CLA and chromium: people lost only slightly more with them than with placebo — 0.88 kg with garcinia, 0.7 kg with CLA (after at least 6 months) and 0.5 kg with chromium. For CLA, the authors write that it did not convincingly show a clinically relevant effect.4,5,6
Weak evidence 13 studies Caffeine: a summary of 13 small studies with 606 people suggests that caffeine slightly lowers weight and body fat. But the results of individual studies varied a lot.7

3Risks

EFSA assessment 800 mg EFSA: in clinical trials, green tea extracts with 800 mg of EGCG a day or more raised liver blood tests (transaminases) — a sign of liver damage. Supplements contain 5–1,000 mg of EGCG per daily dose. EFSA considers green tea prepared the usual way generally safe.8
Data 317 products Over ten years, the US FDA warned about 776 supplements containing unapproved drugs. 317 of them were for weight loss, and 85% of those contained sibutramine.9

Related articles: Weight loss.

What to take from this

Sources

Written on , based on studies available at that date. Newer research may change the conclusions.

  1. Batsis J. A. et al. (2021). A systematic review of dietary supplements and alternative therapies for weight loss. Obesity 29:1102–1113. doi.org/10.1002/oby.23110
  2. Jurgens T. M. et al. (2012). Green tea for weight loss and weight maintenance in overweight or obese adults. Cochrane Database Syst Rev CD008650. doi.org/10.1002/14651858.CD008650.pub2
  3. Pooyandjoo M. et al. (2016). The effect of (L-)carnitine on weight loss in adults: a systematic review and meta-analysis of randomized controlled trials. Obes Rev 17:970–976. doi.org/10.1111/obr.12436
  4. Onakpoya I. et al. (2011). The use of Garcinia extract (hydroxycitric acid) as a weight loss supplement: a systematic review and meta-analysis of randomised clinical trials. J Obes 2011:509038. doi.org/10.1155/2011/509038
  5. Onakpoya I. J. et al. (2012). The efficacy of long-term conjugated linoleic acid (CLA) supplementation on body composition in overweight and obese individuals: a systematic review and meta-analysis of randomized clinical trials. Eur J Nutr 51:127–134. doi.org/10.1007/s00394-011-0253-9
  6. Onakpoya I., Posadzki P., Ernst E. (2013). Chromium supplementation in overweight and obesity: a systematic review and meta-analysis of randomized clinical trials. Obes Rev 14:496–507. doi.org/10.1111/obr.12026
  7. Tabrizi R. et al. (2019). The effects of caffeine intake on weight loss: a systematic review and dose-response meta-analysis of randomized controlled trials. Crit Rev Food Sci Nutr 59:2688–2696. doi.org/10.1080/10408398.2018.1507996
  8. EFSA ANS Panel (2018). Scientific opinion on the safety of green tea catechins. EFSA Journal 16:e05239. doi.org/10.2903/j.efsa.2018.5239
  9. Tucker J. et al. (2018). Unapproved pharmaceutical ingredients included in dietary supplements associated with US Food and Drug Administration warnings. JAMA Netw Open 1:e183337. doi.org/10.1001/jamanetworkopen.2018.3337

This is general information and does not replace a doctor. Food supplements are not medicines; buy them from trusted sellers and talk to a doctor if you are ill or take medicines.