Green Tea Extract

Meta-analyses show a genuine but trivially small effect on weight and fat oxidation, and modest lipid improvements. The concerning part is the safety record of concentrated extracts, which is materially different from that of the beverage.

Green tea is one of the genuinely good things you can drink. Green tea extract is a different proposition, and the difference is the entire point of this entry.

The efficacy claims first, because they are modest enough to settle quickly. Meta-analyses of green tea catechins for weight loss find an effect that is statistically detectable and practically negligible — on the order of a kilogram over twelve weeks, often less, and smaller still in trials outside Japan where habitual caffeine intake differs. Fat oxidation rises measurably during exercise. Lipid profiles improve slightly. None of this is nothing, and none of it justifies the "fat burner" framing the ingredient is sold under.

The safety picture is where this becomes worth writing about. Concentrated green tea extract has accumulated a substantial case series of drug-induced liver injury — hundreds of reports, ranging from asymptomatic enzyme elevation to acute liver failure requiring transplantation. A comprehensive United States Pharmacopeia review concluded the association was credible enough to warrant a cautionary label, and several European countries have restricted high-dose products. The risk appears concentrated in high-dose extracts, taken fasted, sometimes with a genetic susceptibility in how the liver conjugates catechins.

Crucially, this pattern does not appear with the beverage. Populations that drink several cups of green tea daily show no comparable signal, because brewing delivers a fraction of the catechin dose that a capsule does, spread across the day, with food. Concentration is the variable that changed.

So the practical advice writes itself. Drink green tea — the epidemiology is favourable, the catechins arrive at sane doses, and it is pleasant. If you want an extract anyway, keep it at or below roughly 500 mg of catechins daily, take it with food rather than fasted, avoid it entirely if you have any liver condition or take hepatotoxic medication, and stop immediately at any sign of jaundice, dark urine, unusual fatigue, or right-upper-quadrant pain. This is one of the few supplements on this list where the downside is materially worse than the upside.

How it works

EGCG, the principal catechin, inhibits catechol-O-methyltransferase, prolonging the action of noradrenaline and modestly raising thermogenesis and fat oxidation — which is why it appears alongside caffeine in fat-burner formulas. It is also a potent antioxidant and, at high concentrations, a pro-oxidant in hepatocytes, which is the leading explanation for its hepatotoxicity.