Dietary Estrogen in Dog Food

Phytoestrogens are plant-derived, nonsteroidal compounds with estrogenic activity. Soybeans, a common ingredient in commercial dog foods, are their primary source. Phytoestrogens have both positive and negative effects on the health of humans and other animals. To evaluate for phytoestrogens, these investigators analyzed 12 commercial foods that contained soybeans or soybean fractions and 12 commercial foods without soybean-related ingredients listed on the label. The latter types of food did not have detectable levels of the assayed phytoestrogens. The lowest concentration was found in the foods containing only soy fiber or soybean oil-in fact, one of the foods with soy fiber contained no detectable phytoestrogens. Products were found that contained phytoestrogens in amounts similar to those that have biological effects in other species. It is not known what effect they have in dogs.

COMMENTARY: Since soy is such a common ingredient in pet foods, it is important to know more about the phytoestrogens they contain. Clinical studies are needed to both determine the bioavailability of phytoestrogens in dog food and whether these compounds have any biological effect in dogs.

Identification and concentration of soy phytoestrogens in commercial dog foods. Cerundolo R, Court MH, Hao Q, Michel KE. AM J VET RES 65:592-596, 2004.