MetabolismMostly marketing

Green tea extract, EGCG

Also called: EGCG, epigallocatechin gallate, catechins, Camellia sinensis, decaffeinated green tea extract.

A concentrated extract sold to burn fat, whose effect on weight is minimal and whose real issue is the liver.

What it is

Green tea contains catechins, including EGCG, and caffeine: a brewed cup provides about 240 to 320 mg of catechins and 45 mg of caffeine according to the NIH. Capsule extracts concentrate these catechins at doses no cup reaches. People buy them for weight loss, energy and as an antioxidant.

What the label does not say

The liver is the real risk. LiverTox classes green tea extract in category A (a well-established cause of clinically apparent liver injury): more than 100 cases reported, onset 1 to 6 months, acute hepatitis most often reversible on stopping, but cases of fatal liver failure or transplant. Health Canada concluded in 2017 that a link is possible and requires labels to mention rare, unpredictable cases of liver injury, restriction to ages 18 and over, and taking it with food.
The EFSA (2018) puts the dose at which a significant rise in transaminases was observed in trials at 800 mg of EGCG per day and above, as a supplement. A Minnesota trial cited by the NIH (843 mg of EGCG per day for 12 months) raised liver enzymes compared with placebo.
On weight, the Cochrane review reports, in trials conducted outside Japan (6 trials, 532 participants), a difference of 0.04 kg, not significant; the meta-analysis cited by the NIH on catechins plus caffeine gives 1.38 kg and 1.93 cm of waist circumference over 12 weeks compared with caffeine alone. Catechins without caffeine show nothing.
A green tea extract is not a cup of tea: the EFSA generally considers infusions safe, whereas the liver injury cases involve concentrated extracts, hence the United States Pharmacopeia's recommendation, echoed by LiverTox and the NIH, to take them with food.

The forms on the shelf

Brewed tea: the EFSA generally considers infusions prepared the traditional way safe, with an average intake of 90 to 300 mg of EGCG per day and up to 866 mg in heavy drinkers.
Dry extract standardized for catechins or EGCG: it is this concentrated form, taken on an empty stomach, that is implicated in the liver injury.
Decaffeinated extract: the caffeine is removed, but catechins alone showed no effect on weight in the meta-analysis cited by the NIH; the modest effect measured comes from the combination of catechins and caffeine.
Combined slimming products: LiverTox reports that one such product was withdrawn in Spain and France in 2003 and that others have been implicated in rare acute liver injury.

Published reference values

No recommended intake. EFSA threshold: rise in transaminases observed at 800 mg of EGCG per day and above as a supplement.
Caffeine: a brewed cup provides about 45 mg; a non-decaffeinated extract contains it too, to be added to the day's coffee.
Effects reported in the Cochrane review: nausea, constipation, abdominal discomfort, rise in blood pressure, judged mild to moderate; two hospitalizations among 1,945 participants.
Warning signs required by Health Canada: jaundice, abdominal pain, dark urine, sweating, nausea, unusual fatigue, loss of appetite. Stop and consult.

When

With food, never on an empty stomach, in adults only according to Health Canada. Brewed tea remains the least risky way to consume it.

Keep apart from

Non-heme iron: tea polyphenols markedly reduce its absorption according to the Linus Pauling Institute; it is better not to take the tea or the extract with a meal rich in plant iron or with an iron supplement.

To mention to a professional

Liver disease or a history of liver injury, use of hepatotoxic medications, iron deficiency anemia, sensitivity to caffeine, hypertension, pregnancy and breastfeeding: check with a health care professional.

What it is sold for, and what the data show

Green tea extract is sold as a fat burner. The trials give between 0 and 1.4 kg over 12 weeks depending on whether caffeine is counted, and nothing for catechins alone; on the other side, a well-established cause of liver injury at concentrated doses. Brewed tea keeps the catechins without the risk, and without the promise.

From the plate first

A cup of brewed green tea provides about 240 to 320 mg of catechins and 45 mg of caffeine according to the NIH; the average intake of a green tea drinker ranges from 90 to 300 mg of EGCG per day according to the EFSA.

Sources

Educational information, drawn from the sources above. It does not replace the advice of a health professional, who remains the reference for your situation, your medications, pregnancy or breastfeeding.