A study in mice found that the primary polyphenol found in green tea (epigallocatechin gallate, or EGCG) decreased diet-induced obesity by decreasing energy absorption and increasing fat burning (Klaus et al 2005).

Another study in mice evaluated the effects of caffeine, polyphenols, and L-theanine, the three major components of green tea.

Additive benefits were found from green tea polyphenols, caffeine, and theanine on fat accumulation (Zheng et al 2004).

Furthermore, another study showed that feeding 4 percent green tea powder to mice resulted in weight loss as well as lower concentrations of total cholesterol in the liver, triglycerides in serum and liver, and fatty acids in serum (Sayama et al 2000).

A well-known study examined whether or not green tea extract, rich in caffeine and polyphenols, could increase 24-hour energy expenditure and fat oxidation in humans. On separate occasions, subjects were randomly assigned to one of three treatments: green tea extract and caffeine (90 mg EGCG and 50 mg caffeine), caffeine (50 mg), and placebo, which were ingested at breakfast, lunch, and dinner. The results showed that treatment with the green tea extract (which included caffeine) resulted in a significant increase in metabolic rate, as evidenced by a significant increase in 24-hour energy expenditure (Dulloo et al 1999).

An open-label trial demonstrated that after three months, green tea extract decreased body weight by 4.6 percent and waist circumference by 4.48 percent (Chantre et al 2002).

Green tea is available in both caffeinated and decaffeinated forms. For more safety information about green tea, please see "Safety Caveats" at the end of this chapter.