Balancing Phytoestrogens for Companion Pets

By on


phytoestrogens dogs


A phytoestrogen is an estrogen-like compound occurring naturally in plants of the legume family and in grains, vegetables, and fruits. 

Phytoestrogens have been widely researched for their health benefits to help prevent certain types of cancer and other aging-related disorders but are also believed to be endocrine disruptors. 

In the instance of phytoestrogens, they mimic or interfere with estrogen produced in the body by binding to estrogen receptors. This could lead to delaying puberty and infertility. Endocrine disruptors have also been linked to developmental problems, autoimmune diseases and some neurodegenerative diseases. And, this is just what we know now.

However, don’t panic. You may hear people say they avoid phytoestrogens, but this could be like saying they gave up breathing for the month. 

Again, phytoestrogens are naturally occurring and enable vegetables, grains, grasses, legumes, herbs and fruits to grow. They are passed up through the food chain too. So, eating meat would still expose you to them.

The items that need to be considered are: the class of phytoestrogen and its subclass; how it is metabolized in the body; if the health benefits outweigh the risks; and, the amount of phytoestrogen in the food source. 

Currently, four phytoestrogen classes have been recognized: flavonoids, lignans, coumestans, and stilbenes. Within those classes, there are further subclasses and even further divisions. 

On top of that, certain foods could be a member of more than one class of phytoestrogen and more than one subclass. 

Due to this vast network, I decided to look at a few properties of these foods and decide if the health benefits outweigh the potential risks.

Blueberries the Superfood

If you have read Canine Nutrigenomics: The New Science of Feeding Your Dog for Optimum Health (Dodds and Laverdure, 2015), you will know that I am a huge advocate of blueberries. In fact, Diana and I list them as a superfood for dogs because of their antioxidant properties (a cellular protectant from oxidative damage caused by the free radicals that are found in phytoestrogens). Research shows that antioxidants defend against heart disease and cancer, as well as other chronic inflammatory conditions including obesity and “leaky gut”.  

Blueberries are a part of the flavonoid, stilbene and lignan classes. They are further classified in the flavonoid class as anthocyanidins, which have anti-inflammatory properties and have been shown to interfere with various stages of carcinogenesis by reducing cancer cell proliferation and inhibiting tumor formation. Within the stilbene class, blueberries are proven to contain pterostilbene, which is another powerful antioxidant that has been shown to contain potent cancer-fighting properties in animal studies.

The Complexity of Soy

Soy is a member of the phytoestrogen class flavonoid, isoflavone subclass, and that drills down to both genistein and diadzein. Possibly the most researched food these days, soy products at this point in time are not as beneficial as blueberries for a few reasons. First, the phytoestrogen levels found in soy compared to other foods are off the charts. One peer-reviewed study (McClain et al., 2005), found a direct link between genistein and decreased sexual hormonal activity in dogs. Another downer, soy isoflavones inhibit the effects of thyroid peroxidase which disrupts normal thyroid function and can possibly enhance estrogen-dependent breast cancer.

It has also been postulated that our bodies need to be able to convert soy’s daidzein to equol in the gut to reap the benefits associated with increasing bone density. Currently, only 30-50% of humans have the bacteria necessary to convert daidzein. The bacteria seems to develop over time with consuming soy-rich diets amongst other factors such as your personal genetics. A study was performed on dogs (Juniewicz et al., 1988) to find out if they could convert daidzein to equol, which proved they can. However, I doubt the efficacy and current relevance of this study since it was completed almost 30 years ago and commercial dog food diets back then were often high in soy.

On the flip side, these same phytochemicals can modulate epigenetic mechanisms to protect against other types of cancers such as colorectal and prostate. So, one could reason that the consumption of soy benefits are linked to life-stage, metabolic conversion and/or sex.

Particularly for dogs, soy is strongly linked to a range of food sensitivities from mild-to hyper-reactive. Overall, I prefer not to feed soy to our dogs or cats. Plus, they may already be getting trace amounts phytoestrogens through mixed tocopherols, a popular preservative in commercial pet foods.  

Quercetin Supplement

Quercetin is also categorized as a flavonoid and flavon within that class. Quercetin down-regulates the mutant p53 gene, which promotes cell division and cancer. It also suppresses expression of the RAS gene which, when hyperactivated, can express cancer-causing oncogenes.  

A Note about Peas

Peas are also high in phytoestrogens. I normally would not have a problem with pets eating peas, but many commercial pet foods include peas or pea fiber protein as a staple ingredient in all of a company’s products. If your pet does not have a food intolerance to lentils (high cross-reactivity with peas) and you can ensure that peas are rotated out of the diet every three months, then you can feed it to your pet so long as you are not planning to use him or her for breeding.

Broccoli – Interesting

Broccoli is also bucketed in the phytoestrogen flavonoid section and the subclass, flavonol.

Groundbreaking research has suggested recently that when the body converts broccoli and similar cruciferous foods, that it can either form beneficial or harmful estrogen metabolites. The compound that is formed in the body during the digestion of foods that contain the nutrient indole-3-carbinol is called Diindolylmethane (DIM). DIM helps the body break down estrogen into a beneficial type of metabolite that has antioxidant properties. Conversely, DIM may also reduce the levels of harmful estrogen metabolites, which is beneficial because they are associated with an increased risk for obesity and breast cancer. The exact process is unknown, but some of the benefits are likely derived from the fact that DIM helps to balance the sex hormones, estrogen and testosterone. Whether or not DIM has the same effect on dogs and cats at this time is unknown.

A Final Note on Endocrine Disruptors

The industrial age brought us several nice conveniences to help sustain life if not improve its quality. Or, did it? Endocrine disruptors may be lurking in many everyday products that we are now completely dependent on such as plastic bottles, metal food cans, detergents, flame retardants, toys, cosmetics, and pesticides.

Yes; several bans around the globe have occurred to reduce the use of many manmade pesticides like DDT (dichlorodiphenyltrichloroethane) or plasticizers like DEHP (Di(2-ethylhexyl) phthalate). Public awareness has curbed – but not banned the use of – bisphenol A.

But, is this really enough? I don’t think so. I believe the cumulative effect of phytoestrogens and these manmade environmental hazards have caused an uptick in the known endocrine disrupting diseases and disorders. I also suspect there will be a significant rise of these conditions in human and pet populations over the next several decades.

What to do? At the end, it all comes down to balance. Curb the use of the unnecessary environmental toxins as much as possible. Limit vaccinations responsibly. (I still believe – based on scientific studies and the gravity of heartworm disease – that preventatives are necessary where the environmental conditions warrant them.) Weigh the medically beneficial pros of foods against the cons to help you and your companion pets live long, healthy lives.

W. Jean Dodds, DVM
Hemopet / NutriScan
11561 Salinaz Avenue
Garden Grove, CA 92843


Ashton, Megan. “Diindolylmethane Benefits.”, 27 June 2015. Web. 06 Mar. 2016.

Bacciottini, Lucia, Alberto Falchetti, Barbara Pampaloni, Elisa Bartolini, Anna Maria Carossino, and Maria Luisa Brandi. “Phytoestrogens: Food or Drug?” Clinical Cases in Mineral and Bone Metabolism 4.2 (2007): 123-30. CIC Edizioni Internazionali. Web. 06 Mar. 2016.

Dodds, Jean, DVM, and Diana Laverdure, MS. Canine Nutrigenomics: The New Science of Feeding Your Dog for Optimum Health. Wenatchee: Dogwise, 2015. Print.

“Endocrine Disruptors.” National Institute of Environmental Health Sciences, n.d. Web. 06 Mar. 2016.

Juniewicz, P.E., S. Pallante Morell, A. Moser, and L.l. Ewing. “Identification of Phytoestrogens in the Urine of Male Dogs.” Journal of Steroid Biochemistry 31.6 (1988): 987-94. Web.

Lampe, Johanna W. “Is Equol the Key to the Efficacy of Soy Foods?” The American Journal of Clinical Nutrition 89.5 (2009): 1664S-667S. American Society for Nutrition. Web. 06 Mar. 2016.

McClain, RM, E. Wolz, A. Davidovich, and J. Bausch. “Subchronic and chronic safety studies with genistein in dogs.” Food and Chemical Toxicology 43.10 (2005): 1461-482. National Center for Biotechnology Information. U.S. National Library of Medicine. Web. 06 Mar. 2016.

Patisaul, Heather, and Wendy Jefferson. “The Pros and Cons of Phytoestrogens.” Frontiers in Neuroendocrinology 41.4 (2010): 400-19. Web.

“Phytochemicals.” Micronutrient Information Center. Linus Pauling Institute | Oregon State University, n.d. Web. 06 Mar. 2016.

“phytoestrogen”. Unabridged. Random House, Inc. 15 Feb. 2016.

“Phytoestrogens.” E.hormone. Tulane University, n.d. Web. 06 Mar. 2016.

Share this message: