Numerous studies indicate that EGCg, a major compound in whole green tea leaves, may have weight-gain-prevention and weight-loss effects.
One report published in 2005 notes that green tea has the ability to help people maintain their body weight after a significant weight loss. This means that after losing weight through dieting or exercise, drinking green tea may be able to help you keep from gaining the weight back. In this study, 76 overweight people were put on dramatic weight loss diets for four weeks, after which time they were allowed to go back to a regular diet, but with half of the subjects also taking a special green tea supplement. The result was that those treated with green tea were less likely to gain back the weight that they had lost. While the report concludes that much of this effect can be attributed to the caffeine content of green tea, the researchers maintain that at least part of the weight maintenance was due the compound known as epigallocatechin gallate (or EGCg) which is the primary compound found in green tea.
These results confirm the conclusions reached by a similar study published six years earlier in 1999. In this experiment, ten men were subjected to three separate trials in order to see if they would experience increased fat oxidation when taking a combination of caffeine and EGCg. In the first of the three trials, the men were given a pill containing caffeine only; in the second trial they were given a pill containing both caffeine and EGCg; in the third trial they were given a placebo. The researchers found that the men were most able to burn fat when given the pill containing both caffeine and EGCg, indicating once again that green tea’s fat fighting abilities cannot be attributed solely to its caffeine content.
A third study , published in 2000, did not involve caffeine consumption at all. It consisted of tests on laboratory rats to see if their body weight would be reduced after an injection of isolated EGCg. Not only did their body weight decrease, but their overall food intake was reduced, indicating that EGCg can work to reduce appetite. These effects were seen not only in normal-sized rats but in obese rats as well. Furthermore, the researchers noted that the rats lost weight in proportion to the dose of EGCg they were given, losing the most weight with the highest doses. It should be noted that in this case study, the researchers found only EGCg to be effective and not the other similar catechins found in green tea.
Since each of these three studies has singled out EGCg as the active ingredient in green tea’s ability to prevent unwanted weight gain, it should be noted that this compound is available in the greatest amounts in whole green tea leaves as opposed to brewed green tea. This was made evident by a data table compiled by the USDA in which whole green tea leaves were shown to have 100 times as much EGCg as brewed green tea. http://www.nature.com/oby/journal/v13/n7/full/oby2005142a.html  http://www.ajcn.org/cgi/content/full/70/6/1040?maxtosh%20ow=&HITS=10&hits=10&RESULTFORMAT=&searchid=1&FIRSTINDEX=0&so%20rtspec=relevance&volume=70&firstpage=1040&resourcetype=HWCIT  http://endo.endojournals.org/cgi/content/abstract/141/3/980?ijkey=75ab0baed3fbaf1e1d599951528e0cb8445cfb06&keytype2=tf_ipsecsha  http://www.nal.usda.gov/fnic/foodcomp/Data/Flav/flav.pdf