Flavonoids are a group of phytochemicals with antioxidant effects in humans. As flavonoid intakes increase, the risk of many Western lifestyle diseases decreases. In particular, high intakes of flavonoids have been shown to decrease the risk of cardiovascular disease and cancer. The flavonoids present in tea belong to the catechin group of flavonoids (also called flavan-3-ols) and this group of flavonoids may also have fat loss effects. Animal studies using mice show that catechins are able to increase resting metabolic rate in a synergistic way with the caffeine and L-theanine in green tea. In this way the catechins may have direct fat loss effects. However, there is evidence that catechins may also have some regulatory role in appetite. Catchins are found in cocoa as polymers called proanthocyanidins, and one study has shown an 8 % decrease in ad libitum food intake following consumption of cocoa rich dark chocolate. Cocoa fed to rodents has been shown to decrease body weight although the mechanism here is not understood.
Green tea contains 4 flavan-3-ols (catechins). These are catechin (C), epicatechin (EC), epicatechin gallate (ECG) and epigallocatechin gallate (EGCG). Catechins belong to the flavonoid group of phytochemicals and are therefore good antioxidants, like most flavonoids. This relates to their polyphenolic ring structure (polyphenols are literally three phenolic rings joined together to form A, B and C rings). This structure also makes flavonoids good metal chelators. Some evidence indicates that flavonoids may regulate gene expression, which indicates they could modify cell function directly. It is unclear why catechin have weight loss effects. However certain flavonoids are known to bind directly to receptors in the brain, For example apigenin and chrysin can bind to the benzodiazepine receptor in the brain and elicit anti-anxiety effects. The possibility therefore exists that the catechin in tea may have direct effects on the central nervous system. This may explain some of their appetite suppressing effects.
Of the catechins in green tea, epicatechin may be the primary weight loss compound. Human clinical studies show that epicatechin is able to decrease food intake when fed to healthy young adults if given as a beverage before a pizza meal. The amount of epicatechin that was required to have this effect was 1.6 mg of epicatechin per kg body weight. In a typical 75 kg adult, this would equate to 120 mg of epicatechin. The catechin content of brewed green tea is roughly 10 mg per 100 mL and so a typical cup of tea (300 to 500 mL) may contain 30 to 50 mg of epicatechin. Therefore the amount of epicatechin used in this study to cause an appetite suppressing effect is obtainable in a normal diet if the individual consumes 3 to 5 cup of tea per day. These results support animal studies that show that a single dose of epicatechin can decrease appetite significantly in rats. These rats were fed epicatechin regularly after having gained weight from eating a western diet, and the epicatechin reversed that weight gain. Something to think about.
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