Once a product starts to get credit for doing everything, there is a chance you may be in the crackpot zone.  If so, look for the downfall of green tea in 2012 because a new study says the Epigallocatechin-3-gallate (EGCG) in green tea prevents weight gain.  Add that on to claims that EGCG prevents arthritis, Alzheimer's, diabetes and breast cancer and even slows AIDS.

But if it works, it works.  Obese mice that were fed a compound found in green tea along with a high-fat diet gained weight significantly more slowly than a control group of mice that did not receive the green tea supplement, said Joshua Lambert, assistant professor of food science in agricultural sciences at Penn State.

The researchers fed two groups of mice a high-fat diet. Mice that were fed EGCG along with a high-fat diet, gained weight 45 percent more slowly than the control group of mice eating the same diet without EGCG. 
In addition to lower weight gain, the mice fed the green tea supplement showed a nearly 30 percent increase in fecal lipids, suggesting that the EGCG was limiting fat absorption, according to Lambert.  Note that they were consuming the EGCG in about 10 cups of green tea, so you really need to like the stuff.

"There seems to be two prongs to this," said Lambert. "First, EGCG reduces the ability to absorb fat and, second, it enhances the ability to use fat."

The green tea did not appear to suppress appetite. Both groups of mice were fed the same amount of high-fat food and could eat at any time.

"There's no difference in the amount of food the mice are eating," said Lambert. "The mice are essentially eating a milkshake, except one group is eating a milkshake with green tea."

Lambert, who worked with Kimberly Grove and Sudathip Sae-tan, both graduate students in food science, and Mary Kennett, professor of veterinary and biomedical sciences, said that other experiments have shown that lean mice did not gain as much weight when green tea is added to a high fat diet. However, he said that studying mice that are already overweight is more relevant to humans because people often consider dietary changes only when they notice problems associated with obesity.

"Most people hit middle age and notice a paunch; then you decide to eat less, exercise and add green tea supplement," said Lambert.

Study published in Obesity.