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February 23, 2000
February 23, 2000
Scientists at the University of Chicago's Tang Center for Herbal Medicine Research have found that a major chemical component of green tea caused rats to lose up to 21 percent of their body weight. Rats injected with epigallocatechin gallate (EGCG) derived from green tea leaves lost their appetites and consumed up to 60 percent less food after seven days of daily injections.
In previous studies, EGCG was observed to reduce the size of breast and prostate tumors in mice, a result that led Shutsung Liao, PhD, Director of the Tang Center and professor in the Ben May Department for Cancer Research and colleagues to study the effects of EGCG on the endocrine systems of rats.
The current study, published in the March issue of Endocrinology, reports that rats injected with EGCG for just a few days experienced significant changes in the blood levels of several hormones, including leptin. "This result was significant because previous research has shown that leptin is involved in controlling the appetite," says Liao, "but the result was very unexpected."
When Liao injected normal rats with EGCG, their leptin levels in the bloodstream went down. This should have caused the rats to eat more. Instead, they ate less.
Next, Liao injected rats whose leptin receptors had been desensitized. These rats were engineered to be immune to changes in leptin concentration. When these leptin- numb rats were injected with EGCG, the results were the same: the rats ate less.
"This reinforced the idea that leptin has nothing to do with the decrease in food intake. We suspect that EGCG may work through other hormonal systems that control appetite and body weight that we don't know about yet," says Liao. "We are currently investigating on a molecular level how EGCG works to suppress appetite."
In addition to decreased food intake and body weight, rats injected with EGCG had lower levels of testosterone (70 percent less in the bloodstream) and insulin. "These results may not have been a direct result of EGCG since food restriction could also cause these hormones to drop," said Liao.
To test whether the EGCG was the direct cause of the hormonal changes, Liao compared the EGCG-injected rats to controls who were fed a restricted diet. These rats showed similar decreases in testosterone and insulin levels, but some hormones changes were seen in the EGCG-injected rats that were not observed in the restricted diet rats.
"This means that some changes are directly due to EGCG," Liao said.
Because of the lower testosterone levels, the researchers also noticed that EGCG injections caused the prostate of healthy rats to decrease in weight. In some rats, the prostate lost 70 percent of its original weight. Lowering the testosterone level may be helpful in preventing the enlargement of prostate and the growth prostate cancer in older people, Liao said.
EGCG was less effective when rats were given the substance orally. "This may be because of poor absorption of EGCG or possibly because of an interaction with food," said Liao. The researchers also found that EGCG reduced abdominal and subcutaneous (just under the skin) fat, and blood levels of lipid, glucose and cholesterol, but did not appear to cause liver damage.
Although oral administration of EGCG was ineffective even after 14 consecutive days of large doses, Liao thinks that long-term oral consumption may mimic some of the results obtained with injection.
"A person would have to drink green tea almost constantly to obtain these results," said Liao. "And since some of the hormonal changes we saw in the rats could have negative effects, especially in younger people, I don't recommend drinking large quantities of green tea for everybody. Much more research needs to be done," cautioned Liao.
Other researchers on this study included Yung-hsi Kao, PhD, research associate in the Ben May Department for Cancer Research, and Richard Hiipakka, PhD, senior research associate in the Ben May Department for Cancer Research.