What is green tea extract (catechins)?

In one line

Green tea extract is a supplement ingredient made by pulling catechins, a plant compound, out of green tea leaves and concentrating them far beyond what a cup of tea holds.

What is green tea extract (catechins)?
The name on diet supplement labels
You see 'green tea extract', 'catechins' or 'EGCG' on the labels of fat-loss supplements and diet products. This post explains what green tea extract is, how it differs from a cup of tea, and what research found about its effects and its risk of liver injury.
In short
Green tea catechins, concentrated
Green tea extract is made by pulling a compound called 'catechins' out of green tea leaves and concentrating it. It is mostly sold as pills or capsules, and it is also common in diet products that mix many ingredients.
What is green tea?
Tea leaves that are not fermented
Green, black and oolong tea all come from the leaves of the same tea plant. For green tea, the leaves are steamed or pan-fried and dried, without fermenting. Black tea is fermented, and oolong tea is partly fermented.
Catechins
Most of green tea's plant compounds, led by EGCG
Green tea contains a group of plant-made compounds called 'polyphenols', and most of them are catechins. Among catechins, the most common in green tea and the most studied is 'EGCG'. The strength of green tea extract is often given as how many mg of EGCG it contains.
How it differs from a cup of tea
Supplements hold up to 1,000mg a day
People who drink green tea get on average 90 to 300mg of EGCG a day. Green tea extract supplements, depending on the product, hold up to 1,000mg of EGCG a day. Even though both come from green tea, a supplement can deliver far more at once than tea.
Why people take it
The weight-loss effect was very small
Green tea extract is used in diet supplements in the hope that its catechins and caffeine reduce body weight. But pooling trials of green tea products, the weight lost was so small that it did not matter in daily life. Pooling only trials done outside Japan, there was no difference from a fake pill.
Liver injury
Severe cases and liver transplants were reported
Liver injury has been reported after taking green tea products, mostly extracts in pills or capsules. In a US record of liver injury cases, most cases judged to be caused by green tea had 'jaundice', yellowing of the skin and eyes, about one in three were severe, and some needed a liver transplant.
Dose and liver tests
Liver tests rose at 800mg a day or more
When the liver is damaged, 'liver test' numbers in a blood test go up. The European Food Safety Authority concluded that taking 800mg or more of EGCG a day as a supplement raises liver test numbers. In a trial that gave women past menopause about 840mg a day for twelve months, the risk of abnormal liver tests was 7 times that of a fake pill.
On an empty stomach
Much more EGCG reaches the blood
Taking green tea extract all at once on an empty stomach put much more EGCG into the blood than taking it in split doses with food. So the US Pharmacopeia (the group that sets quality standards for medicines and supplements) added a warning to its green tea extract standard: do not take on an empty stomach, do not use with liver disease, and stop if signs of liver trouble appear.
Who gets liver injury more easily
The immune gene form HLA-B*35:01
A little over 70% of people whose liver was injured by green tea had this gene form. Among people with liver injury from other drugs, and in the general population, it was about one in ten. This gene is involved in the body's immune system, which means an immune reaction is tied up in green tea liver injury.
Common myth
Is it as safe as green tea because it comes from green tea?
No. Many people think diet supplements are safer than medicines, but green tea extract is not the same as tea. Brewed green tea in usual amounts was judged safe, and reports of liver injury from it were rare. Cases of liver injury came mainly from concentrated extracts taken as pills or capsules.
Summary
A concentrated green tea catechin ingredient
Green tea extract is a supplement ingredient that concentrates green tea catechins, especially EGCG, far beyond tea. Unlike tea, concentrated extracts have been linked to reports of severe liver injury. Related terms: catechins, caffeine, liver tests.