Estrogenic activities in rodent estrogen-free diets

Diets lacking soy and alpha-alpha derivatives considered to be estrogen-free by classical bioassays (uterotrophic assay and vaginal opening) revealed to contain considerable amounts of compounds able to transcriptionally activate the estrogen receptors (ERs)and stimulate luciferase expression in several organs of the ERE-Luc reporter mouse. By molecular imaging,we show that ER activation is present in non-reproductive organs to an extent similar to what observed with the administration of 17β-estradiol and it is not influenced by orchidectomy or treatment with an aromatase inhibitor. This, together with the use of a completely synthetic diet, proves that the activation of ERs observed is due to estrogenic compounds present in commercial diets and it is not a secondary event determined by food assumption and metabolism. The pervasiveness of estrogenic compounds in nature poses the question on how relevant and how necessary is the daily ingestion of natural compounds active through the ERs to the maintenance of a correct metabolism in both male and female mammals.