Mint-family herbs trimmed BMI and waist, not body fat

The Lamiaceae family — mints, sages, thymes and their relatives — has an unusually long history in traditional medicine across many cultures, and extracts from these plants are widely sold as metabolic supplements. Traditional use is not evidence of effect, however, and the individual randomised trials in this area tend to be small, short and scattered across different genera and doses. What has been missing is a pooled estimate that asks whether these plants shift body size and fat distribution in the people most likely to take them: adults with metabolic syndrome or its component conditions. This review set out to provide it, and to grade how confident the answer deserves to be.

The authors searched PubMed, Scopus, ISI Web of Science, ProQuest, SID and MagIran from inception to 15 July 2025 for randomised controlled trials comparing Lamiaceae plants with placebo in adults aged 18 or over with metabolic syndrome or related conditions, including obesity, type 2 diabetes, dyslipidaemia and non-alcoholic fatty liver disease. Two reviewers independently screened, extracted data and assessed risk of bias with Cochrane RoB 2.0. Random-effects meta-analyses were run with prespecified subgroup analyses by duration (up to 8 weeks versus longer), metabolic status and genus, plus meta-regression. Certainty was graded with NutriGrade, the review followed PRISMA 2020 and was pre-registered on PROSPERO.

Twenty trials with 2,445 participants qualified. Pooled analyses showed statistically significant reductions in size-based indices, namely BMI and body weight, and in proxies of central adiposity, namely waist circumference and waist-to-hip ratio. Directly measured body fat mass did not change significantly, which is the most important null in the set. Both short courses of up to 8 weeks and longer ones reduced BMI, while the effects on waist circumference and weight appeared mainly in overweight or obese participants. Subgroup work pointed to Salvia and Zataria for BMI, with waist circumference reduced only by Salvia, but meta-regression found no significant linear association between duration, metabolic status or genus and the anthropometric changes. NutriGrade rated confidence high for pooled BMI and weight, and moderate for waist-to-hip ratio.

The pattern here is a familiar one in supplement research: measures of overall body size move, while the measure that would confirm fat loss does not. The authors attribute the discrepancy to a shortage of trials, short intervention periods and indirect measurement methods rather than concluding that nothing happens to fat. Their bias appraisal tempers the story too, with half the trials showing unclear allocation concealment. Benefits in participants with diabetes were not demonstrated. The genus-level signals are explicitly labelled exploratory and rest on few trials, so which plants, at what preparation and for how long, remain open questions.

This is a reason to think mint-family supplements can nudge body size measures in people with metabolic syndrome, but not a reason to expect them to reshape body composition. The effects are described as modest by the authors themselves, and the review's own conclusion positions these plants as a supportive adjunct within multicomponent lifestyle programmes rather than a standalone intervention. Because BMI and waist circumference can shift for reasons other than fat loss, and body fat mass did not move significantly, the honest reading is that the mechanism is unresolved. Anyone with diabetes should note the evidence there was judged insufficient.