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Green Tea and Metabolism: What EGCG Does, Caffeine Content and Safety

The science behind one of the world's most studied drinks.

Quick answer

Green tea contains catechins, mainly EGCG, along with caffeine. Together they have been studied for a modest effect on energy expenditure and fat oxidation, and green tea has been researched for its role in glucose metabolism. A cup of brewed green tea has about 30 to 50 mg of caffeine, less than coffee. Green tea extracts are concentrated, so they should be taken with food and avoided by people with liver problems unless a doctor approves.

Key takeaways

Green tea is often called a metabolism booster. Here's what the research actually looks at, and what it doesn't promise.

What's in green tea

Catechins

Plant antioxidants, the most abundant of which is epigallocatechin gallate (EGCG).

Caffeine

A moderate amount that supports alertness and works alongside catechins.

L-theanine

An amino acid associated with calm focus, which may smooth out caffeine's edge.

Green tea vs coffee

Green teaCoffee
Caffeine per cupAbout 30–50 mgAbout 80–100 mg
Main antioxidantsCatechins (EGCG)Chlorogenic acids
L-theanineYesNo
Metabolism researchModest effectsModest effects

Green tea and blood sugar

Studies have examined green tea catechins in relation to fasting glucose and insulin sensitivity, with mixed but encouraging results. Green tea works best as part of an overall pattern of balanced meals, activity and good sleep. GlycoDefender includes green tea leaf extract alongside gymnema, chromium and African mango.

Safety: concentrated green tea extracts have rarely been linked to liver problems, especially at high doses on an empty stomach. Limit total caffeine if you are sensitive, pregnant or have a heart condition, and ask your doctor if you take medication.

Sources

  1. National Center for Complementary and Integrative Health (NCCIH) – "Green tea."
  2. Hursel R. et al. – "The effects of green tea on weight loss and weight maintenance: a meta-analysis," International Journal of Obesity, 2009.
  3. U.S. Food and Drug Administration – "Spilling the beans: how much caffeine is too much?"

Common questions

Does green tea boost metabolism?

Its catechins and caffeine have shown modest effects on energy use in studies.

How much caffeine is in green tea?

About 30 to 50 mg per cup, less than coffee.

Does GlycoDefender contain green tea?

Yes, it includes green tea leaf extract, which naturally contains caffeine.

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