A very large body of work has shown positive effects of
green tea on a wide range of biological effects that improve health. Most research has focused on EGCG as the predominant polyphenol in
green tea responsible for thermogenic and
antioxidant effects. There is evidence linking
EGCG to thermogenesis and fat oxidation in humans. For example, one study showed a significant incre
ase in 24 hour energy expenditure withdose of 90 mg of EGCG which was no different than the increase with 400 mg.The dose of EGCG associated with increased thermogenesis in most studies ranged from 90 to 300 mg/day. The magnitude of increase in energy expenditure in humans is between 80 and 180 kcal per day, which could easily translate into improved weight loss over several months. For example in one study men had two-fold greater weight loss and four-fold greater reductions in subcutaneous and visceral fat in the abdomen compared to placebo after 12 weeks of green tea supplementation (690 mg catechins/day). Dose response and bioavailability studies indicate that single doses of up to 1,600 mg EGCG are well tolerated and result in rapid circulating levels of EGCG. Since EGCG is the primary active compound, methods to increase its concentration in plasma would hypothetically enhance its effectiveness. Researchers from India tested various nutrients in combination with
green tea extract to determine if they could enhance the bioavailability of EGCG. It was shown that people consuming the same amount of EGCG had significantly higher plasma concentrations of EGCG when they also consumed
quercetin and red onions. It remains unclear exactly how these nutrients enhance bioavailability of EGCG but the authors hypothesized that the nutrient combination enhanced EGCG stability. The results provide evidence that certain nutrients like
quercetin can be used to enhance the effects of EGCG.