From Ergo-Log

Many herbs, as well as onions, red wine, green tea and the peel of red apples, contain large amounts of the flavonoid quercetin. According to an Italian study, this compound has an anti-oestrogenic effect. In a test tube it's possible to see that quercetin intercepts the estradiol receptor's signal to the cell. Supplements manufacturers have been aware of the anti-oestrogenic effect of quercetin for years. Quercetin is an ingredient of Estrox, for example, a supplement made by Ori Hofmekler's Defense Nutrition. [defensenutrition.com] Hofmekler is the person who thought up the Warrior Diet. He's a pioneer of the intermittent fasting trend, but has also written about anti-oestrogenic foods and supplements. There is plenty of circumstantial evidence for the anti-oestrogenic effect of quercetin. A Polish epidemiological study for instance has shown that women that drink large amounts of green tea have less estradiol in their bodies. [Br J Nutr. 2006 May;95(5):989-95.] In a Korean test-tube study ginkgo inhibited the effect of estradiol [J Steroid Biochem Mol Biol. 2006 Aug;100(4-5):167-76.] and in a similar American study the same effect was attributed to goji. Green tea, ginkgo and goji all contain quercetin – and lots of other substances too.