Biogenetics Laboratories

Several dietary supplements and natural substances have been studied for their fat-burning effects, including:

Green tea. Research has shown green tea supplements can promote modest weight loss-a few pounds in short-term studies of up to 12 weeks, when compared to placebo-and may help prevent weight regain. Catechins, one component of green tea, appear to have a variety of fat-burning effects, including increasing metabolism and the use of fat for fuel, and decreasing the rate at which body fat is created and stored. Green tea has a good track record of safe use.

Capsaicin. Capsaicin is the spicy-hot component of red chili peppers, and one randomized trial found that people lost twice the weight taking capsaicin compared with a placebo, over a 12-week period. The total effect was small, however: the capsaicin group lost about 2 pounds compared to a 1-pound loss in the placebo group. Capsaicin appears to increase metabolism, and supplements of up to 6 grams of capsaicin per day are considered safe and are well tolerated by most people.

L-carnitine. Our bodies make and use L-carnitine to transport fat within cells, so that the fat can be burned for energy. Studies support that L-carnitine supplements improve fat burning in the body, but clinical trials have yet to show a weight-loss benefit in obese people. L-carnitine may be useful for improving athletic performance, however, and up to 3 grams per day is considered safe.

New kids on the block

Raspberry ketones. When given to mice on a high-fat, high-calorie diet, raspberry ketones protected against excess weight gain and fat accumulation in the liver. Mice aren't people, however, so keep an eye out for future research, which should clarify what kind of effects raspberry ketones may have for weight-loss in people.

Bitter orange (Citrus aurantium). This product became more popular after the 2004 FDA ban on ephedra supplements. Bitter orange has effects similar to ephedra, including increasing metabolism, blood pressure, and heart rate, which can translate into weight loss. While bitter orange appears to be safe for short-term use-weeks, not months-in healthy adults, it also may have similar adverse effects as ephedra, so use it with caution if you have underlying health issues, such as heart disease, high blood pressure, or diabetes.