Reviewed on 3/24/2009
I can sum up my thoughts on thermogenics in two words: stay away! Manufacturers claim that thermogenic supplements are designed to increase your metabolism (the rate at which you burn calories), suppress your appetite, and promote weight loss. The term "thermogenics" refers to an increased production of heat in the body, yet the safest and most effective way to generate more heat and boost your metabolism is not through a supplement or drug, but with regular physical activity. That said, thermogenic supplements include a variety of stimulants - mostly herbal - alone or in combination. These stimulants, such as caffeine (typically in the form of guaraná, kola, or yerba maté) or ephedrine (in the form of the herb ephedra), purportedly help increase energy levels, suppress appetite, and burn fat.
The FDA has banned ephedra, saying "dietary supplements containing ephedra present an unreasonable risk of illness or injury, and should not be consumed." I have often warned against ephedra (ma huang) and ephedrine, which can be dangerous especially when combined in weight-loss products with other stimulants such as caffeine. In addition to a risk of addiction, ephedra can cause such side effects as irregular heartbeat, insomnia, and elevated blood pressure. As far as weight loss is concerned, don't be surprised if you regain every pound you lose once you stop taking supplements containing ephedra or other stimulants.
Here are some other ingredients commonly used in thermogenic formulas and my objections to them:
- Garcinia cambogia: The active ingredient here is hydroxycitric acid (HCA). Some data from animal studies suggest it may suppress appetite as well as the formation of fats and cholesterol in the liver, but there's no evidence that it's effective for weight loss in humans.
- Bitter orange (Citrus aurantium): Here, the main active ingredient is synephrine, a stimulant analogous in action to the nasal-spray drug Neo-Synephrine and similar to ephedrine. I don't think there's enough good scientific research to say that bitter orange promotes weight loss in humans. In fact, a group of Italian researchers recently found that lab rats given bitter orange ate less and lost weight but also developed heart abnormalities and died as the dose increased. The researchers cautioned that bitter orange may be dangerous especially when used by the elderly, the obese, and those with heart problems.
- Pyruvate: This naturally occurring enzyme is the main ingredient in the weight loss product "Exercise in a Bottle." Promoters claim that pyruvate forces every cell in the body to work harder whether or not you're exercising. The Federal Trade Commission has filed multiple complaints against the makers of "Exercise in a Bottle" for false claims made on a now-banned television infomercial.
Although you may seem to lose weight in the short-term with thermogenic supplements, you won't maintain this weight loss without eating less and exercising more. Since several of the ingredients are potentially dangerous and the evidence of their effectiveness is weak, I would avoid thermogenics and instead concentrate on cutting back on calories and portion sizes, and increasing physical activity.
Andrew Weil, M.D.