Soy products are very popular in human health foods, and soy is also a common ingredient in dog food. However, soy has been linked to a few health problems in dogs and other species (including humans).
Are soy-based foods safe for your dog? What about treats? The answer depends on whom you ask — as well as the dog in question.
The Case for Soy
Dog food sold in the US has to pass certain minimum standards for health and digestibility. Soy and soy products generally pass the tests. This means that dogs can digest soy, and soy has not been proven to do anything negative to dogs who eat it.
Soy is the most complete vegetable source protein typically used in pet food manufacturing, and is a more affordable source of protein than meat or eggs. As such, dog food companies like soy, because it helps them to stay competitive with prices — and the saving are passed on to you!
The estrogen-like chemicals in soy products might have some small health benefits for dogs with specific medical conditions, though not much research has been done on this topic yet.
Some dogs with dietary sensitivities and allergies to other foods can eat soy, making soy-based dog foods useful for them. You can also find hypoallergenic diets with hydrolyzed soy protein. This hydrolyzed protein is helpful for lots of dogs with food allergies since the protein has been broken down so the immune system doesn’t recognize it.
The Case Against Soy
The plant estrogens that make soy medically useful for some conditions also make it possibly dangerous for others. Some experts suggest that excessive soy consumption contains enough estrogen that it might provide some estrogen-like activity in your spayed or neutered pet. Depending on their stage of life and medical conditions, this may not be ideal.
Soy consumption may also contribute to slightly lower thyroid hormone levels, so if your dog has hypothyroidism this may not be the best food.
Lastly, there are some dogs who have soy allergies and sensitivities, though this is rare.
Not All Soy is Alike
Traditionally, soybeans were fermented, a process that dramatically reduced their plant estrogen level and made them more digestible.
Modern commercial soy products are often chemically processed or separated into various fractions (to make things like tofu, for example). The use of texturized soy protein-based products are very common in both human and dog foods, and too much of this texturized soy product can lead to loose stools.
The Bottom Line
There is a lot of “maybe” here — soy has not been officially proven to be “unsafe” in dogs. So far all we can say is that soy is a good protein and energy source and acceptable to use in dog food. But like many other things in life, moderation is ideal.
Researching soy products in dog food is difficult, in part because experts sometimes appear to contradict each other. There are many possible reasons for this kind of disagreement, in part because there is a lot we still don’t know, and different people use their judgment to put together the pieces differently.
Any dog who has ever rummaged through the trash, or gone outside unattended, has eaten things a lot worse than soy products. Unless your dog has a particular sensitivity, soy is a fine ingredient for their dog food. A soy-based dog food, or a homemade diet featuring soy, is a more complicated question, and has actually been used for therapeutic diets that include liver problems and allergies.
For help formulating your own, educated opinion on the topic, speak with a vet who has a particular interest in diet (no vet knows everything, after all!), or a board-certified veterinary nutritionist.
More on Dog Nutrition
Are Fruits and Vegetables Good for Dogs?
10 of the Best Rated Dog Foods
Dog Treat Recipes
This information is for informational purposes only and is not meant as a substitute for the professional advice of, or diagnosis or treatment by, your veterinarian. It has however been reviewed for accuracy by Dr. Joe, a board certified veterinary nutritionist and graduate of Cornell University's program for Veterinary Medicine.