Also known as: EGCG, Epigallocatechin gallate, Camellia sinensis extract, Green tea catechins, Polyphenols
Fat MetabolismGood evidence
A concentrated catechin extract standardised to EGCG, widely used in fat metabolism formulas. The effect on energy expenditure is real but small, and concentrated extracts carry a documented liver safety consideration that dictates a firm upper limit.
Typical dose
300.0–500.0 mg per day
With food; avoid late in the day if the extract retains caffeine
What it is
Green tea extract is produced from the leaves of Camellia sinensis, the same plant that yields black and oolong tea. Green tea leaves are minimally oxidised after picking, preserving the catechin content that oxidation would otherwise convert into other compounds.
The principal catechin is epigallocatechin gallate, or EGCG, typically comprising the majority of the catechin fraction. Extracts are standardised either to total polyphenols, commonly 40 to 98 per cent, or to EGCG content specifically. EGCG standardisation is the more meaningful figure.
Products differ substantially in whether caffeine is retained or removed. Decaffeinated extracts isolate the catechin effects, while caffeinated extracts deliver both, and much of the perceived thermogenic effect in the latter comes from the caffeine rather than the catechins. This distinction matters for both efficacy expectations and safety.
How it works
The most cited mechanism involves inhibition of catechol-O-methyltransferase, the enzyme that degrades noradrenaline. By slowing that breakdown, EGCG prolongs noradrenaline signalling, which supports thermogenesis and fat mobilisation. This mechanism also explains the frequently observed synergy with caffeine, which acts on the same pathway from a different angle.
Catechins also inhibit digestive enzymes including pancreatic lipase and alpha-amylase, modestly reducing absorption of dietary fat and carbohydrate. The magnitude of this effect at supplemental doses is small.
Beyond metabolism, EGCG has substantial antioxidant activity and influences a range of signalling pathways, which accounts for the breadth of research interest in areas from cardiovascular health to cognition. Bioavailability is a persistent limitation, with only a small fraction of an oral dose reaching circulation as intact EGCG.
What the evidence shows
Meta-analyses of green tea catechins for weight management generally report a statistically detectable but clinically small effect, typically on the order of one to two kilograms over 12 weeks relative to placebo. Effects appear more pronounced when combined with caffeine, and some evidence suggests response varies with habitual caffeine intake and with ethnicity.
Trials measuring energy expenditure directly have found increases in the region of a small percentage of daily total, which is consistent with the modest body composition findings. This is a real effect, but it is not the transformative one implied by fat burner marketing.
Cardiovascular research on green tea consumption is more encouraging, with observational and interventional work reporting favourable effects on lipid measures and blood pressure. Much of that literature concerns tea drinking rather than concentrated extract supplementation, and the two are not equivalent in either dose or safety profile.
Dosing
Typical supplemental range is 300-500 mg daily of extract, delivering roughly 150-300 mg of EGCG. Dose against declared EGCG content rather than extract weight.
The safety ceiling is the governing constraint here. European safety assessment identified 800 mg of EGCG daily from concentrated extracts as the level above which liver injury risk becomes a concern, and that figure should be treated as a firm upper limit rather than a target.
Taking it with food rather than on an empty stomach is advisable. Some bioavailability research favours fasted intake, but the liver safety signal is associated with fasted administration of high doses, which makes the trade-off unattractive.
At a glance
Common forms
Standardised EGCG extract, Decaffeinated green tea extract, Green tea leaf powder, Combined with caffeine in thermogenic blends
Half-life / duration
EGCG plasma half-life approximately 3-5 hours
Timing
With food; avoid late in the day if the extract retains caffeine
Competition status
Permitted — not on the WADA Prohibited List
Category
Fat Metabolism
Safety and side effects
Drinking green tea is safe and unremarkable. Concentrated extracts are a materially different proposition and warrant a clear safety statement rather than reassurance by association with the beverage.
Reports of liver-related adverse effects associated with concentrated green tea extracts have accumulated over many years, prompting formal safety review in Europe and warning requirements in several countries. Risk appears related to high EGCG doses, taking it on an empty stomach, and individual susceptibility. Events are rare relative to the scale of use, but the signal is well documented and should be disclosed on any product supplying concentrated catechins.
Catechins also reduce absorption of iron from plant sources, which is relevant if your iron levels are low. Where the extract retains caffeine, the full caffeine profile applies in addition.
Who should avoid it
Avoid if you have been told your liver is not working normally, or if you take medication that places a load on it. Stop and seek medical advice if you notice yellowing of the skin or eyes, unusually dark urine, abdominal pain or unexplained fatigue. Avoid in pregnancy and breastfeeding. Take care if your iron levels are low, or if you take regular medication. Do not exceed 800 mg EGCG daily from all sources.
This entry is provided for information only. Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. Consult a qualified healthcare professional before use if you are pregnant, breastfeeding, taking medication or under medical supervision.
