Finally, a slimming aid that actually works?

The search for an effective treatment of obesity is understandably intense. Many scientists are looking in the plant kingdom for a solution, but so far none has been forthcoming – as we have already discussed on this blog before (e. g. here, and here). One herbal slimming aid is currently becoming popular: Yerba Mate also called Ilex paraguariensis, a plant many of us know from teas and other beverages. Our review concluded that the evidence for it was unconvincing but that it merited further study. This was 10 years ago, and meanwhile the evidence has moved on.

The aim of a recent study was to investigate the efficacy of Yerba Mate supplementation in subjects with obesity. For this purpose, a randomized, double-blind, placebo-controlled trial was conducted. Korean subjects with obesity (body mass index (BMI) ≥ 25 but < 35 kg/m(2) and waist-hip ratio (WHR) ≥ 0.90 for men and ≥ 0.85 for women) were given oral supplements of Yerba Mate capsules (n = 15) or placebos (n = 15) for 12 weeks. They took three capsules per each meal, total three times in a day (3 g/day). Outcome measures were efficacy (abdominal fat distribution, anthropometric parameters and blood lipid profiles) and safety (adverse events, laboratory test results and vital signs).

During 12 weeks of Yerba Mate supplementation, statistically significant decreases in body fat mass and percent body fat compared to the placebo group were noted significant. The WHR was significantly also decreased in the Yerba Mate group compared to the placebo group. No clinically significant changes in any safety parameters were observed.

The authors concluded that Yerba Mate supplementation decreased body fat mass, percent body fat and WHR. Yerba Mate was a potent anti-obesity reagent that did not produce significant adverse effects. These results suggested that Yerba Mate supplementation may be effective for treating obese individuals.

These are encouraging results, but the conclusions go way too far, for my taste. The study was tiny and does therefore not lend itself to far-reaching generalisations. What would be helpful, is a review of other evidence. As it happens, such a paper has just become available. Its authors evaluated the impact of yerba maté on obesity and obesity-related inflammation and demonstrate that yerba maté suppresses adipocyte differentiation as well as triglyceride accumulation and reduces inflammation. Animal studies show that yerba maté modulates signaling pathways that regulate adipogenesis, antioxidant, anti-inflammatory and insulin signaling responses.

The review authors concluded that the use of yerba maté might be useful against obesity, improving the lipid parameters in humans and animal models. In addition, yerba maté modulates the expression of genes that are changed in the obese state and restores them to more normal levels of expression. In doing so, it addresses several of the abnormal and disease-causing factors associated with obesity. Protective and ameliorative effects on insulin resistance were also observed… it seems that yerba maté beverages and supplements might be helpful in the battle against obesity.

I am still not fully convinced that this dietary supplement is the solution to the current obesity epidemic. But the evidence is encouraging – more so than for most of the many other ‘natural’ slimming aids that are presently being promoted for this condition by gurus like Dr Oz.

What we needed now is not the ill-informed, self-interested voice of charlatans; what we need is well-designed research to define efficacy, effect size and risks.