Caffeine
Common dose: 100-200 mg taken before aerobic activity
Used prudently, caffeine can increase the intensity of your workouts and may be used when dieting to enhance fat loss. It increases levels of cyclic adenosine monophosphate (cAMP), which results in increased blood-sugar levels and increased lipolysis (liberation of free fatty acids from fat cells). The latter gives rise to increased energy and work output during long-term bouts of exercise, such as an extended aerobic-training session.

Caffeine & Ephedra
Common dose: 75-100 mg caffeine with 300 mg ephedra (standardized to about 20 mg ephedrine)
Because of their synergistic effects on accelerating metabolic rate, these two are commonly combined and sold as thermogenic stimulators/fat-loss supplements, and are widely available in health-food stores. While the combination of ephedra and caffeine could be considered a natural fat-loss aid, the two ingredients have been associated with side effects like increased heart rate, insomnia and nervousness. If you're on antidepressants, have high-blood pressure or diabetes, heart problems or a thyroid condition, or are currently taking medication for asthma, this one's definitely not for you. Also see "Ephedra" listing.

Chitosan
Common dose: 2 grams/day
Widely advertised on television, chitosan prevents the absorption of fat from your gastrointestinal tract. A unique fiber derived from shellfish, chitosan sounds attractive but has some pretty significant negatives. First, science has demonstrated that not all fats are bad; in fact, many are important for the production of hormones and are necessary for your health and well-being, so you don't really want to block their uptake. Another point to consider: Chitosan may prevent the absorption of fat-soluble vitamins, which are essential for healthy bones, hair and skin. Finally, it may cause severe stomach discomfort and diarrhea.

Chromium Picolinate
Common dose: 200 mcg/day
Chromium is a mineral that can affect insulin, a hormone that plays a major role in muscle growth and fat metabolism. Though a normal amount of this mineral exerts a mild effect on your body, taking additional amounts has never been shown to induce a change in body composition. The latest studies show chromium doesn't enhance weight loss or improve muscle tone. If your diet lacks chromium, taking a supplement may help you burn fat or add muscle, but only if you're deficient.

Citrus Aurantium (CA)
Common dose: 325 mg/day
A fruit in the citrus family, CA contains a naturally occurring active ingredient called synephrine. It can increase your body's ability to burn fat and may exert a mild hunger-suppressant effect. It reportedly has fewer side effects than ephedra because of less stimulation of the nervous system. Some in the supplement industry describe it as "ephedra lite."

Ephedrine can be very difficult to come by because of new federal and state regulations, but it can still be found in over-the-counter stimulants sold at convenience stores. When the synthetically derived version is present, it's usually combined with an expectorant like guaifenesin. Herbal ephedra can be found at most health-food stores. Look on the label for either mahuang (also spelled ma huang) or ephedra; that's how you know the herbal form is present in your fat-burner. If you have high blood pressure or certain other health conditions, you probably shouldn't use ephedra or ephedrine, so check with your doctor.

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