Soy Protein

By Rania Gollakner, BS, DVM, MPH

What is soy protein?

Soy protein is protein sourced from soybeans and is sometimes used as a dietary supplement in pets. Soy contains many types of proteins, but isoflavones are a specific category of proteins found in soy that are used for their estrogenic effects. Other effects of isoflavones may include antioxidant, anticancer, antimicrobial, and anti-inflammatory activity. In animals, soy protein has been used in weight management, metabolic disease management, cancer management (especially lymphoma), and hormone-related conditions such as prostatic hypertrophy and urinary incontinence.

Dietary supplements are substances that can be used to supplement the diet, such as vitamins, minerals, amino acids, herbs, botanicals, enzymes, and probiotics. While many supplements are sold over the counter, they still contain ingredients that have biological effects that should be managed by your veterinarian. Follow your veterinarian’s directions and cautions very carefully as their directions may be significantly different from those on the label.

There are differences in how countries regulate supplements. In the United States, these substances are not as vigorously regulated by the FDA as other medications, which means they can be sold without the manufacturer proving their effectiveness, safety, and without a guarantee of consistent or accurately reported ingredients. In Canada, products that have been evaluated for quality, safety, and effectiveness by Health Canada and authorized for sale will have a license number on the label.

How effective is soy protein?

Limited studies in animals have been performed, but there is anecdotal evidence that soy protein works to treat hormone-related diseases, metabolic diseases, cancers, and inflammatory/immune-mediated diseases by exerting effects on the immune system and hormone receptors. Studies in humans have also shown similar anecdotal evidence, and also include evidence for beneficial cardiovascular effects.

"It should be noted that while soy protein has many potential beneficial effects, there is concern that high doses for long periods of time may also cause detrimental effects."

It should be noted that while soy protein has many potential beneficial effects, there is concern that high doses for long periods of time may also cause detrimental effects (such as an increase of certain cancer types). Consult with your veterinarian regarding the potential benefits versus the potential risks for your pet.

How is soy protein given?

Soy protein is given by mouth as an ingredient in pet food, or as a supplement in the form of a powder, tablet, or capsule. It may be given with or without food; however, if stomach upset occurs when given on an empty stomach, give future doses with food.

What if I miss giving my pet the supplement?

If you miss a dose, give it when you remember, but if it is close to the time for the next dose, skip the dose you missed and give it at the next scheduled time, and return to the regular dosing schedule. Never give your pet two doses at once or give extra doses.

Are there any potential side effects?

Studies are limited for this supplement and therefore information regarding side effects is also limited. In humans, side effects may include nausea, vomiting, diarrhea, constipation, gas. Serious side effects include allergic reactions such as skin rash, facial swelling, or difficulty breathing.

Are there any risk factors for this supplement?

Studies are limited for this supplement and therefore information regarding risk factors is also limited. Soy protein should not be used in pets that are allergic to it, or in pets that are pregnant or nursing. It should be used cautiously in pets that have thyroid, liver, or kidney disease. Because there is some conflicting evidence about soy protein and its effects on cancer, use cautiously and only after discussing the risks versus the benefits with your veterinarian.

Are there any drug interactions I should be aware of?

The following medications should be used with caution when given with soy protein: chemotherapies, hormone therapies, insulin, levothyroxine, monoamine oxidase inhibitors (MAOIs), or warfarin.

Vitamins, herbal therapies, and supplements have the potential to interact with each other, as well as with prescription and over the counter medications. It is important to tell your veterinarian about any medications (including all vitamins, supplements, or herbal therapies) that your pet is taking.

Is there any monitoring that needs to be done with this supplement?

There is no specific monitoring that needs to be done while your pet is taking this medication. Your veterinarian may monitor your pet to be sure that the medication is working. Monitor your pet at home for serious side effects.

How do I store soy protein?

In general, store soy protein supplements in a cool place, protected from light and moisture. There are many formulations and manufacturers of this supplement, so always follow the specific directions on the product label.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility.

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