Although green tea is an ancient beverage, it is more popular in modern times that it has ever been before. Now that modern science has uncovered the various antioxidants and other beneficial compounds in green tea, it has risen from the rank of beverage to nutraceutical, with its effects on weight loss hogging the spotlight. It was originally thought that the caffeine content was responsible, but further exploration revealed it to be the work of a particular phytochemical. The catch is that the dose needs to be high, and preferably not oral.
Epigallocatechin gallate, or EGCG, is a polyphenol found in green tea along with catechin, epicatechin, proathocyanidins and others. A typical cup of tea brewed from dried leaves yields about 300 to 400 mg of polyphenols, but only a small portion of that is EGCG, which is considered the most beneficial compound of the group. Numerous health effects have been attributed to EGCG, including weight loss -- but the research was conducted with such high concentrations of EGCG that you are unlikely to get enough from drinking green tea alone. Fortunately, many supplement stores carry EGCG extracts, and many diet pills include EGCG extract as an ingredient.
Research has shown that EGCG may help increase calorie burn and help the body use stored fat for energy, although the exact mechanism is unclear. A 2000 study at the University of Chicago showed that rats reduced their calorie intake by 60 percent after seven daily EGCG injections, allowing them to lose 21 percent of their body weight. Researchers believe that the EGCG may alter the levels of "hunger hormones," thus reducing the appetite. The catch is that the rats were given an injection of EGCG, and the results were not as promising when the EGCG was given orally. It is unclear whether the body may not absorb EGCG fully from the digestive tract, but if an oral extract didn't work, that leaves little hope for the lower concentrations provided by oral tea consumption.
There is no established dose for EGCG, partly because the research has been all over the map. Dr. Ronald Hoffman mentions a French study that found results using 90 mg of EGCG three times daily, while a 2007 study in the "Journal of the American College of Nutrition" found that twice-daily doses of 150 mg reduced resting heart rate and blood glucose levels, but did not affect weight loss. The University of Maryland Medical Center recommends up to 750 mg per day of a standardized extract, but also recommends up to three cups of green tea per day to provide 320 mg of polyphenols. Because EGCG is but a small part of the overall polyphenol content, you're more likely to get a high enough dose by using an extract.
The most successful research into EGCG and weight loss has used injections rather than oral administration. This is not practical for home use, so extracts are recommended over tea for having a higher EGCG concentration. Long-term oral use may mimic the results of an injection, which means that EGCG is not a quick fix -- results may take time, and the EGCG supplement must be a part of an overall diet and exercise program. Follow the directions on the label of whichever extract you buy, and consult your doctor before using it if you are taking medications or have any chronic condition. High doses of EGCG extract are not known to cause any untoward side effects, but drinking large amounts of green tea exposes you to high amounts of caffeine, which can cause reactions in sensitive people.