About Green Tea

Parts used and where grown

All teas (green, black, and oolong) are derived from the same plant, Camellia sinensis. The difference is in how the plucked leaves are prepared. Green tea, unlike black and oolong tea, is not fermented, so the active constituents remain unaltered in the herb. The leaves of the tea plant are used both as a social and a medicinal beverage.

Active constituents

Green tea contains volatile oils, vitamins, minerals, and caffeine, but the primary constituents of interest are the polyphenols, particularly the catechin called epigallocatechin gallate (EGCG). The polyphenols are believed to be responsible for most of green tea’s roles in promoting good health.

Green tea has been shown to mildly lower total cholesterol levels and improve the cholesterol profile (decreasing LDL "bad" cholesterol and increasing HDL "good" cholesterol).

Are there any side effects or interactions?

Green tea is generally free of side effects.

Green tea catechins, especially EGCG, make up approximately thirty percent of the dry weight of green tea leaves. Of the catechins, EGCG is the most abundant one in green tea leaves.

The catechins in green tea are responsible for the possible health benefits of the plant. These catechins are antioxidants with EGCG appearing to be the most power antioxidant of all the green tea catechins.

Fat Oxidation: Green tea supplementation may help with weight control. Plant ingredients in green tea, such as caffeine and catechin polyphenols, may increase 24-hour energy expenditure and fat oxidation in humans and help with sympathetic release of noradrenaline and management of obesity. Green tea polyphenolics have been found to inhibit the action of amylase, a carbohydrate-digesting enzyme present in saliva.

In a small double-blind, placebo-controlled study with 60 middle-aged obese women (30 to 45 years old), subjects were placed on a diet of 1,800 calories daily and randomly assigned to either a green tea supplement group or the placebo group. Capsules were taken at each meal for 30 days (250 mg x8/day in 3 divided doses). After two weeks, the green tea group had lost twice as much weight as those on placebo. After 4 weeks of treatment, the women in the green tea group had lost 3 times as much weight (2.90 kg) as those on placebo (0.94 kg). Compared to the placebo group, the green tea group also showed a significantly greater reduction in waist size (-2.10±1.37 cm vs. –0.48±0.97 cm), and in their blood triglyceride levels compared to the placebo group also a significant decrease (-2.10±0.19g/L vs. –0.03±0.14g/L). No side effect, including sleep loss, were reported.

Ten healthy men were given 50 mg caffeine and 90 mg of epigallocatechin gallate or 50 mg caffeine or placebo on 3 different occasions. Relative to placebo, the green tea extract resulted in an increase in 24-hour energy expenditure (4%) and a decrease in 24-hour respiratory quotient (from 0.88 to 0.85) without any change in urinary nitrogen. Twenty-four hour urinary norepinephrine excretion was 40% higher than placebo. Overall, researchers concluded that green tea extract might play a role in body composition via sympathetic activation of theromogenesis, fat oxidation or both.

Conclusions: Green tea has been found to have thermogenic properties and promotes fat oxidation beyond that explained by its caffeine content per se. The green tea extract may play a role in the control of body composition via sympathetic activation of thermogenesis, fat oxidation, or both.