An In Vitro Comparison of Estrogenic Equivalents Per Serving Size of Some Common Foods

The public assumes that some foods, such as milk and ground beef from cattle receiving steroidal implants, are associated with estrogenic hormones, while other foods are presumed "safe" or nonestrogenic. Here, we investigate these assumptions by assessing the relative estrogenic activity of a serving size of four foods: skim milk (8 oz), rice (48 g dry wt) in cooking bag, ground beef patties from steers raised with or without hormone implantation (quarter lb each, 114 g), and tofu burgers (isocaloric to beef burger, 198 g), using an in vitro assay (E-Screen). Mean picogram (pg) estradiol equivalents (E2Eqs) on a serving basis were as follows: skim milk 120; rice 400; rice prepared in cooking bag 370; rice boiling bag alone 4 pg per bag, ground beef burger (obtained from the tissue of cattle that had received no hormone implants) 389, beef burger (obtained from cattle that had received hormone implant) 384, and tofu burger 1,020,000. Rice E2Eqs were highly variable, but the plastic cooking bags provided by the manufacturer added negligible E2Eqs. The source of estrogenic activity in rice may have been due to contamination with the mycotoxin zearalenone. The E-Screen E2Eqs of tofu burger extracts agreed with those predicted based on chemical concentrations of the most estrogenic component times their E2Eq factor. While a tofu burger contained around three times the estrogenic activity of a daily dose of estrogen replacement therapy (125 mg, Premarin®, 303,000 pg); the other foods--a quarter pound ground beef burger at approximately equal calorie count, a serving of milk, or rice, were all at least 750-fold less estrogenic. PRACTICAL APPLICATION: When consuming the recognized serving size of a food, how much estrogenic activity can we expect? While the public assumes that some foods, such as milk and ground beef from cattle receiving steroidal implants, are associated with estrogenic hormones, other foods are presumed "safe" or nonestrogenic. Using one assay, a tofu burger contained three times the estrogenic activity of a dose of hormone replacement therapy commonly prescribed for women after hysterectomy or menopause (Premarin®); while other foods--a quarter pound ground beef burger at approximately equal calorie count, a serving of milk, or rice, were all at least 750-fold less estrogenic.