Thermogenics are a popular class of dietary supplements commonly used in weight loss programs. By definition, a thermogenic increases metabolic rate by slightly raising body temperature. While there is no official standard for defining a thermogenic, dozens of herbal and nutritional supplements have been noted to increase metabolic rate.
Stimulants
The majority of stimulants, including caffeine, can be classified as thermogenics because they slightly increase the production of thermogenin. Some herbs, such as yerba mate, contain caffeine as well as another thermogenic stimulant, tetradecylthioacetic acid. These may increase fat-burning power by speeding metabolism.
Ephedra, a powerful herbal containing the thermogenic stimulant ephedrine, was very popular as a component of weight-loss supplement programs. However, due to a high rate of serious adverse reactions, the Food and Drug administration banned the sale of all ephedrine-containing products in 2004.
Yohimbe
The popular African herb yohimbe (and its extract, yohimbine) is commonly used as a male-enhancement product, but it also acts as a thermogenic. Yohimbe acts as a hemodilator and PDE-4 inhibitor, and often causes sweating, flushing, insomnia, and other stimulant-like side effects. By boosting the metabolism, yohimbine may assist with weight loss.
Yohimbine was a component of the popular Hydroxycut product line, a thermogenic brand which was recalled and reformulated in May 2009. The newer version of the product, dubbed Hydroxycut Advance, contains no extracts of yohimbe. It is not clear if yohimbe was a causative factor of the side effects associated with the original Hydroxycut line.
Synephrine
Relatively new to the thermogenic marketplace, synephrine is an increasingly popular component of many newer weight-loss supplements. Synephrine is derived from the peels of certain citrus fruits, and seems to increase the body's production of thermogenin, leading to an increase in temperature, metabolic rate and weight loss.
Synephrine is especially popular in weight loss products for body-builders, and anecdotal evidence has suggested that it provides a more noticeable temperature increase than most other thermogenic supplements. Like many thermogenics, synephrine may be associated with a euphoric or mood-elevating effect.
Fucoxanthin
Fucoxanthin is one of the only non-stimulant thermogenics currently on the market. This relatively recent discovery is considered to be safer than other thermogenics because it does not appear to have any noticeable effect on blood pressure. Preliminary evidence suggests that it is a safer alternative to other temperature-elevating herbs and compounds.
Because it is a component of brown seaweed, sometimes used in oriental cuisine, some nutritionists have speculated that fucoxanthin is partially responsible for lower rates of obesity in Asian countries. While this may be a factor, dietary and lifestyle considerations are a more likely explanation.
Dangers
Herbal and nutritional dietary supplements are not approved by the FDA, and people with medical conditions are advised to avoid taking any over-the-counter supplement for weight reduction unless they have been advised by a qualified physician. Thermogenics and stimulants are associated with some side effects.
The use of any stimulant thermogenic, including especially caffeine or yohimbine, may be associated with increased levels of anxiety or agitation in people who are sensitive to these effects. Thermogenics have also been associated with insomnia, palpitations and cardiac arrhythmia, especially in people taking high doses. People with serious heart conditions can experience severe and potentially life-threatening reactions to strong stimulants.
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