When a newly proclaimed "superfood," such as green tea, captures the attention of retailers and consumers as a potential panacea for all manner of health ills, an onslaught of studies are typically launched by profiteers seeking to take advantage of the desire to grow hair, lose weight or improve the physique. Green tea extract may temporarily boost energy, because it contains caffeine, but buyer beware: The evidence linking green tea to fat burning is still rather weak.
About Green Tea
Green tea comes from the same plant as black tea and oolong tea -- Camellia sinensis. It differs from black and oolong tea in that is unfermented. In tea-makers terms, fermentation refers to a process of rolling the dried leaves of the plant to break down fibers and cause oxidation. Because oxidation destroys some of the healthful substances in tealeaves, green tea retains more antioxidant polyphenols than fermented teas.
Green Tea Extract
Green tea extract is a name used for various forms of herbal supplement containing green tea. An extract can be in the form of oil, liquid or powder form. There are no established legal standards for what constitutes a green tea extract, so it's difficult to know exactly what you're purchasing when you buy this product.
The Evidence
Green tea extract contains caffeine, a substance that accounts for any perceived energy boost gained by the product. A number of scientific studies have hinted at a link between green tea extract and weight loss. As far back as 1999, the "The American Journal of Clinical Nutrition," explored the topic with a study that found green tea extract helps control weight through thermogenesis, or fat burning. Studies have continued, and in 2010 the "Journal of the American College of Nutrition" published research showing that green tea extract consumption significantly decreased body weight and body mass index.
The Bottom Line
The U.S. Food and Drug Administration has repeatedly denied requests for permission to list "fat-burning" and "weight loss" as possible outcomes on the labels of green tea extract products, stating that such claims are not supported by reliable scientific evidence. The University of Maryland Medical Center takes a more positive view of green tea extract, stating that it may boost metabolism and burn fat. Consult a doctor if you are considering taking green tea extract, as this substance can interact with a number of prescription medications and is contraindicated for use in those with heart, kidney or psychological disorders, as well as pregnant or breast-feeding women.
References
- University of Maryland Medical Center; Green Tea; Sept. 20, 2010
- "American Journal of Clinical Nutrition"; Efficacy of a Green Tea Extract Rich in Catechin Polyphenols and Caffeine in Increasing 24-h Energy Expenditure and Fat Oxidation in Humans; A.G. Dulloo, et al.; December 1999
- "Journal of the American College of Nutrition"; Green Tea Supplementation Affects Body Weight, Lipids, and Lipid Peroxidation in Obese Subjects with Metabolic Syndrome; A. Basu, et al; February 2010
- U.S. Food and Drug Administration; Warning Letter for Weight Loss Products "Xenadrine CarboCurb"; Joseph R. Baca; Oct. 24, 2004
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