EGCG

EGCG is one of a family of catechins (green-tea flavan-3-ols) but by far the headliner; a cup of green tea delivers a mix of EGCG, EGC, ECG, and EC, with EGCG making up the largest share and doing most of the heavy lifting in the research ^[2]. As a molecule it is a galloylated catechin, which is a fancy way of saying it carries an extra ring of hydroxyl groups that make it both a potent free-radical scavenger and a sticky binder of proteins and metal ions.

The part people chase it for is metabolism. The classic human work paired green-tea catechins with caffeine and found a real bump in 24-hour energy expenditure and fat oxidation beyond what the caffeine alone explained ^[1], which is the basis for EGCG's place in fat-loss and body-composition products. The effect in isolation is modest and shows up best alongside caffeine and exercise; a meta-analysis of catechin plus training found a small added weight-loss benefit rather than a dramatic one ^[6]. It is best treated as a mild lever, not a fat-burner.

Beyond metabolism, EGCG has a broad antioxidant and anti-inflammatory profile. It activates the Nrf2 pathway (the cell's own antioxidant-defense switch) and quiets NF-kB-driven inflammatory signaling, which is the mechanistic story behind its anti-inflammatory action ^[3] and much of the general beneficial-effects literature spanning cardiovascular, metabolic, and neuroprotective angles ^[5]. A lot of this is why it sits in the longevity and healthspan conversation, though much of that remains preclinical or associational.

The honest weak spots are bioavailability and safety. EGCG is poorly and variably absorbed, is unstable at gut pH, and gets heavily metabolized, so blood levels from a dose are low and inconsistent, which is an active area of formulation work (liposomal and phospholipid versions try to fix it) ^[2]. And unlike a cup of tea, concentrated EGCG extracts taken in high doses on an empty stomach have been linked to rare but real cases of liver injury; a formal safety assessment concluded that green-tea extracts are generally safe when taken with food but flagged the fasted high-dose scenario as the risk setting ^[4]. So the practical rule writes itself: keep the dose sane and take it with a meal.