Caffeine study

Thielecke and his co-workers recruited ten healthy overweight and obese men (average BMI of 31.3kg/m2) to participate in the randomized, placebo-controlled, double-blind cross-over trial. The men were randomly assigned then to one of five groups:

Placebo
Low-dose EGCG (300  mg)
High-dose EGCG (600 mg)
Caffeine(200mg)
EGCG plus caffeine (300 mg/200mg).

The men took the supplements for three days, then seven days of washout, and cross-over to another group. At the end of the study, all the men had participated in each group.

Results showed that during two hours after a meal, the low-dose EGCG supplementation was associated with a 33 percent increase in fat oxidation. The high-dose EGCG supplementation produced a non-significant 20 percent increase, compared to placebo. Caffeine alone was associated with a 34.5 percent increase compared with placebo, while the combined EGCG/caffeine supplement boosted fat oxidation by 49 percent.  There is no synergism of low EGCG and 200mg caffeine, stated the researchers.
Commenting on the difference between high and low dose EGCG, the researchers noted that the lower dose may be optimal for affecting energy expenditure and higher doses do not provide any additional effects.
The results obtained for the combination of EGCG and caffeine may be related to the amount of time the compounds remain in the blood, with the so-called half-life of EGCG reported to be about two hours while caffeine has a half-life of about four hours.  Therefore, EGCG affects are early, whereas caffeine affects both early and late post-prandial fat oxidation, added Thielecke and his co-workers.
Support from other science
A recent review from researchers at Pennsylvania State University concluded that the science supporting the weight management potential of green tea and its extracts was (JournalofNutrition,doi:10.3945/jn.109.115972).
Dr Josh Lambert, assistant professor in the Department of Food Science at Penn State told NutraIngredients.com that laboratory studies and small-scale human intervention studies indicate that consumption of tea might promote weight loss, help maintain body weight following weight loss, and prevent the development of some diseases associated with obesity such as diabetes and fatty liver disease.
The effective doses seem to be approximately 200mg per day.
Source:European Journal of Clinical Nutrition Published online ahead of print, doi:10.1038/ejcn.2010.47  Epigallocatechin-3-gallate and postprandial fat oxidation in overweight/obese male volunteers: a pilot study Authors: F.Thielecke, G.Rahn, J.B–hnke, F.Adams, A.L.Birkenfeld, J.Jordan, M.Boschmann