A pilot randomized clinical trial (RCT), was used to identify if consuming polyphenol-rich beverages would alter the composition of breast milk. For 6 days, three groups of lactating women were asked to supplement their beverage intake by drinking and additional serving of soy milk (250mL, 12mg of isoflavones/serving), decaffeinated black tea (300mL, 67mg of catechins/serving), or water (control) every day. Breast milk samples were collected and analyzed for flavonoid concentration, including isoflavones and catechins, as well as total antioxidant capacity. The preliminary study concluded that women who drank soy milk had considerably higher isoflavone content in their breast milk. In contract, the women who drank decaffeinated black tea or water had undetectable changes in isoflavone content within their breast milk. Additionally, all women, regardless of beverage, had no changes in antioxidant capacity. Flavonoids have been proven to prevent certain types of cancer, improve cardiovascular function, and many other health issues. Therefore, drinking one glass of soy milk every day while breast feeding may greatly improve the child’s health.