IntroductionDifferent outcomes of the effect of green tea on weight loss (WL) and weight maintenance (WM) have been reported in studies with subjects differing in ethnicity and habitual caffeine intake.PurposeTo elucidate by meta-analysis whether green tea indeed has a function in body weight regulation.MethodsEnglish-language studies about WL and WM after green tea supplementation were identified through PubMed and based on the references from retrieved articles. Out of the 49 studies initially identified, a total of 11 articles fitted the inclusion criteria and provided useful information for the meta-analysis. Effect sizes (mean weight change in treatment versus control group) were computed and aggregated based on a random-effects model. The influence of several moderators on the effect sizes was examined.ResultsCatechins significantly decreased body weight and significantly maintained body weight after a period of WL (\[mucirc]=-1.31 kg; P<0.001). Inhibition of this effect by high habitual caffeine intake (>300 mg per day) failed to reach significance (\[mucirc]=-0.27 kg for high and \[mucirc]=-1.60 kg for low habitual caffeine intake; P=0.09). Also, the seemingly smaller effect of catechins in Caucasian (\[mucirc]=-0.82 kg) subjects compared with Asians (\[mucirc]=-1.51 kg; P=0.37) did not reach significance. Interaction of ethnicity and caffeine intake was a significant moderator (P=0.04).ConclusionsCatechins or an epigallocatechin gallate (EGCG)-caffeine mixture have a small positive effect on WL and WM. The results suggest that habitual caffeine intake and ethnicity may be moderators, as they may influence the effect of catechins.International Journal of Obesity advance online publication, 14 July 2009; doi:10.1038/ijo.2009.135.