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08.11.2008


Green tea contains insulin booster

The most important bioactive substance in green tea, EGCG or epigallocatechine gallate, induces muscles cells to absorb more glucose. Researchers at the Kyung Hee University in Korea discovered how: like insulin, EGCG [structural formula below] activates the enzyme phosphatidylinositol (PI) 3-kinase.

EGCG
The Koreans did test-tube experiments using rat muscle. When they fed the cells with EGCG as well as glucose, the cells absorbed up to seventy percent more glucose. Interestingly, even at the highest concentration of EGCG, no muscle cells died. This means that EGCG is not cytotoxic.

The graph below shows the effect of increasing doses of EGCG on the absorption of glucose. The researchers used insulin in a concentration of 200 nanomoles in a control group. Exposure was for half an hour.

Green tea contains insulin booster

There are broadly speaking two ways in which muscle cells can absorb glucose. One is via insulin and insulin mimickers, and goes via the P13K pathway. The other goes via the protein AMPK, and becomes more active as a result of physical exercise. That is also why chemical athletes inject insulin after physical activity. After training, muscle cells absorb so much glucose that none gets to the fat cells. If you inject insulin, then the muscle cells absorb glucose even quicker, so your fat deposits donít increase. They do increase if you use insulin at other times.

Because the Koreans wanted to determine the exact mechanism that EGCG uses, they repeated their experiments using two different blockers. One of them, LY294002, blocks the effect of P13K. This is the blocker LY in the graph below. When the Koreans added LY to the muscle cells, the stimulatory effect of EGCG on the glucose uptake stopped: the researchers had the information they needed on how EGCG works.

Green tea contains insulin booster

The researchers are interested to learn more about EGCG and glucose because they are looking for ways to alleviate diabetes-2 through diet and supplements. But the results are of course also interesting for athletes. They add evidence to the claims for green tea products as pre-training energizers, and might also be evidence of after training effects. Green tea stimulates fat burning during cardio sessions. If green tea also increases the uptake of glucose, it makes green tea even more interesting.

Sources:
J Med Food. 2008 Sep;11(3):429-34.