Camellia sinensis · herb
Evidence tier: weak
Rich in catechins (EGCG), provides antioxidant protection, supports metabolic health, fat oxidation, and reduces cardiovascular risk markers
Catechins, chiefly EGCG, are antioxidant polyphenols; the plausible weight and metabolic mechanism is a modest increase in fat oxidation and thermogenesis, amplified by the caffeine the leaf also carries. That mechanism is real in the laboratory and small in people. The liver mechanism is the more consequential one and it is dose dependent: concentrated EGCG, delivered as an extract and often on an empty stomach, reaches liver exposures a brewed cup never approaches, and in susceptible people triggers an idiosyncratic hepatocellular injury.
Weak, and the single most important fact about green tea is a safety fact, not an efficacy one. The drink and the concentrated extract capsule are two different products with two different risk profiles and they must never be spoken about as one thing. NIH LiverTox rates GREEN TEA EXTRACT a likelihood score A, the top of its scale, meaning a well established cause of clinically apparent liver injury, and states that liver injury typically arises within 1 to 6 months of starting the product, that most cases present as an acute hepatitis like syndrome, and that fatal instances of acute liver failure have been described. LiverTox is equally clear about the beverage: drinking green tea has not been associated with liver injury or serum aminotransferase elevations, and cross sectional studies actually associate regular tea drinking with LOWER serum ALT and AST. Europe's regulator drew the same line: EFSA concluded in 2018 that doses of 800 mg EGCG per day or above, taken as a food supplement, produce a statistically significant rise in liver transaminases, and that it was NOT possible to identify a safe EGCG dose from green tea extracts, while catechins from brewed infusions are generally safe. NCCIH adds that liver injury has been reported primarily with green tea extracts in tablet or capsule form, and that genetic variants raising susceptibility affect between 5 and 15 percent of Americans. On efficacy there is very little to defend. The Cochrane review of green tea for weight loss in overweight or obese adults found a small, statistically non significant weight change that, in Cochrane's own words, is not likely to be clinically important, and Cochrane explicitly notes the finding does not apply to cups of tea because every trial used concentrated extract preparations. NCCIH says the effect on body weight is modest at best, that cancer results have been inconsistent, that the coronary heart disease link appears in Asian but not Western populations (an observational association, not a trial result), and that cholesterol falls only to a small extent. Cognition is a separate story that does not belong to green tea: the replicated attention and alertness findings come from ISOLATED L theanine dosed with caffeine, not from drinking or encapsulating green tea.
As a beverage: 1 to 4 cups daily, which EFSA and LiverTox both treat as generally safe. As an extract: there is no dose that can be called safe. EFSA could not identify one, and found signal at 800 mg EGCG per day and above. Any extract capsule should be treated as a liver risk decision, taken with food, and never stacked with other extracts.
As tea: drink 3 to 5 cups daily. As a supplement: take 250 to 500mg of standardised extract (standardised to 50% EGCG) daily with food. Avoid taking on an empty stomach. Take away from iron supplements as catechins inhibit iron absorption.
Onset: ~21 days
Very safe at typical intake (1 to 4 cups/day). Caffeine content (~30 to 80 mg/cup) may affect caffeine sensitive individuals, anxiety, insomnia, palpitations at high intake. Tannins reduce iron absorption, separate from iron supplements or iron rich meals by 2 hours. High dose EGCG supplements (not tea) have rare hepatotoxicity reports, standard green tea is safe. Limit in pregnancy to <2 cups/day (caffeine + EGCG concerns).
Pregnancy: caution
Breastfeeding: caution
Used as a medicinal beverage in China for over 4,000 years. Documented in ancient Chinese texts for its properties as a digestive aid, stimulant, and wound healer. The polyphenol EGCG is one of the most studied plant compounds in modern nutritional science.
Active compounds: EGCG (epigallocatechin gallate), catechins, caffeine, L-theanine
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*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.