Scientific deep-dive
Capsaicin and Capsinoids for Weight Loss: Eight Measures, Eight Nulls
A dose-response meta-analysis of 13 randomized trials and 838 participants found no effect of capsinoids on body weight, BMI, waist circumference, fat mass, fat-free mass, waist-hip ratio, visceral fat or body fat percentage.
Part of Weight-loss supplements and diet trends: what the trials show
Capsinoids, the non-pungent relatives of the compound that makes chili hot, are sold on the theory that they raise energy expenditure. A systematic review and dose-response meta-analysis pooled 13 randomized trials and 838 participants and measured eight things: body weight, BMI, waist circumference, waist-hip ratio, fat mass, fat-free mass, visceral fat area and body fat percentage. None of them changed.[1]
The eight nulls
| Measure | P value |
|---|---|
| Body weight | 0.230 |
| Body mass index | 0.182 |
| Waist circumference | 0.611 |
| Waist-hip ratio | 0.599 |
| Fat mass | 0.946 |
| Fat-free mass | 0.917 |
| Visceral fat area | 0.836 |
| Percentage body fat | 0.973 |
Several of those p values sit close to 1. These are not near-misses in an underpowered analysis; they are results centered on no difference at all.
The subgroup that gets quoted
The same paper reports one positive finding: in trials conducted on overweight participants that lasted twelve weeks or longer, there was a significant and modest reduction in body weight. That sentence is the one you will meet on a product page, usually without the eight nulls it sits inside.[1]
A subgroup finding inside an overall null result is a hypothesis, not a conclusion. Split any dataset enough ways and some slice will reach significance. That does not make it false. It makes it something for the next trial to test, and that is what the authors ask for: well-designed randomized trials with larger samples and longer duration.
What about the brown fat studies?
Capsinoids have been shown to activate brown adipose tissue and to increase energy expenditure in laboratory conditions,[2] and that is the mechanism the marketing rests on. The mechanism is real. The meta-analysis above is what happened when the mechanism was tested against the outcome: eight measures of body composition, none of which moved.
Capsinoids can raise energy expenditure in the lab, yet across 13 trials none of eight body composition measures moved.
For where the evidence sits on other supplements sold for weight, our supplement evidence grader carries a graded entry with its primary study for sixteen of them, our review of GLP-1 supplements covers berberine, lemon flavonoid, saffron and probiotics, and CLA and green tea extract get the same treatment. For what does move body composition during weight loss, see protein targets and the lab panel and bone density and exercise.
Frequently Asked Questions
References
- 1.Sheikhhossein F, Amini MR, Askari M, et al. The effects of capsinoids supplementation on body composition and anthropometric measures: A systematic review and dose-response meta-analysis of randomized controlled trials Clinical Nutrition ESPEN. 2022. PMID: 36513480.
- 2.Yoneshiro T, Aita S, Kawai Y, Iwanaga T, Saito M. Nonpungent capsaicin analogs (capsinoids) increase energy expenditure through the activation of brown adipose tissue in humans American Journal of Clinical Nutrition. 2012. PMID: 22378725.
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