Hot red pepper can make your mouth feel like it's on fire. Yet its value as a fat-burner is frequently overstated.

The burning sensation caused by eating hot pepper comes from capsaicin, a compound found in milligram quantities in many fat-loss products. Besides irritating the mouth, capsaicin can cause gastrointestinal discomfort and nausea and possibly even damage the lining of the stomach in higher doses.

In fat-loss supplements, capsaicin is touted as a "thermogenic" because of its ability to stimulate your metabolism to release more calories in the form of heat. But are the doses found in these products actually capable of producing fat loss? Most likely no, according to scientists like Toshio Moritani, PhD, who has studied capsaicin in humans.

Moritani is director of the Laboratory of Applied Physiology at Kyoto University in Japan. In one of his studies, women ate curried rice containing 3 mg of capsaicin. Though the addition of capsaicin stimulated the subjects' metabolism, this translated into only 10 or 20 additional calories being burned. At this rate, Moritani explains, "It will take a year to lose 1 kg [2.2 lb] of body fat!"(1)

While ingesting larger doses of capsaicin may cause more calories to be burned, the side effects may be intolerable. Anita Belza, PhD, an assistant professor in the Department of Nutrition at the University of Copenhagen, explains, "I think it will probably be quite difficult for a Western population to eat a dosage of capsaicin from food items to obtain a fat-reducing effect." (2) Fuminori Kawabata, a researcher in the Laboratory of Nutrition Chemistry at Kyoto University, puts it more bluntly: "It is impossible for an individual to obtain sufficient amounts of capsaicin from the diet or supplements to enhance fat loss because of the painful stimulation. It is very dangerous." (3)

Jose Galgani, PhD, is an assistant professor in the Department of Nutrition at the University of Chile. He says that subjects have been known to drop out of capsaicin studies because it is so pungent. "In large quantities it can cause stomach discomfort. For this reason there has been interest in studying related compounds known as capsinoids that may have capsaicin's thermogenic effect but without the pungency."(4) Unfortunately, Galgani's studies to date have found no thermogenic effect from capsinoids.

In Belza's studies subjects were given capsaicin in capsule form, sometimes in combination with other ingredients. Notably, when capsaicin was combined with green tea and caffeine (a combination found in a number of supplements), subjects' blood pressure increased. She says that other researchers have reported increases in heart rate in subjects given capsaicin, in addition to the usual reports of gastrointestinal discomfort and nausea.

In summary, the scientific consensus seems to be that, relative to its side effects, capsaicin's calorie-burning (thermogenic) effect is just too weak to produce fat loss. Consumers may therefore be much better off by using a capsaicin-free fat-loss product like BI's 7-Keto Musclean.