What Are Plant-Based Proteins Doing in My Pet's Food?

The last time you were perusing potential new pet foods at the pet supply store did you notice a new trend?

When your dog or cat’s favorite food made a change to their recipe, did they add a new protein source? A plant-based one?

If you’ve noticed plant-based protein in your dog or cat’s food lately, you’re witnessing a trend that has been growing for the past few years: plant protein being used as bolster or replacement for animal protein.

Depending on the quality of the food, plant protein may be an inexpensive filler, a replacement for an animal protein, or could be a way to boost protein levels for a lower cost, among other reasons.

Sometimes a pet food company may tell you that plant protein is just as good as animal protein in your pet’s food. However, that just isn’t the case. Just because protein percentages in chicken and corn protein may seem the same, bioavailability isn’t.

While some plant proteins like pea protein can be a solid ingredient in a premium pet food, plant protein can rarely completely replace animal protein for dogs or cats.

(We say “rarely” because there are some high quality vegetarian pet foods out there, but those foods are very carefully formulated and in Calvin & Susie’s opinion are not appropriate for all animals or all life stages. Unless guided by a vet, it is the rare situation where a dog – never a cat – does better on vegetarian food. But we digress.)

With corn, soy, peas, and potato protein all appearing in pet foods on the low-end, mid-range, and premium end, it can be hard to determine if the protein in your pet’s food is appropriate.

So to help you out a bit, and aid you in making the right decision for your pet, here is a guide to those plant proteins in your dog or cat’s food.

But first…

Why is protein so important in a dog or cat’s diet?

Long story short, protein is the building block of your pet’s body. It’s need for tissue and bone growth (especially in puppies and kittens), energy, and a healthy immune system. Protein helps your dog or cat build and repair muscle, as well as helps lactating dogs ad cats produce milk. Without proper protein consumption, a dog or cat cannot maintain adequate hormone levels, and they cannot grow, mature, or thrive.

Without adequate protein your pet’s body will basically shut down, cannibalizing their body’s own protein (tissue, organs, etc.) to survive.

When considering a protein for your pet, one must keep in mind the biological appropriateness of the protein (protein for a cat is not appropriate protein for a guinea pig), the nutritional value, the absorbability, the digestibility, and if it has any sensitivities, toxic properties, or allergy triggers.

Soy Protein

But soy isn’t listed as an ingredient in my pet’s food, so we’re OK right?

Not necessarily. Soy may not be listed as “soy protein” or “soy” in the ingredients list. It may be listed as “textured vegetable protein” (TVP) or even “vegetable broth” (when in doubt, contact the pet food company – a reputable company should have no problem clearly answering your questions), among other monikers.

Soy is often touted as a great way to bulk up a pet food and add inexpensive protein. However, the issues that can arise with soy protein may outweigh the seeming benefits.

First of all, like with all plan proteins, soy protein is simply not as biologically available as animal protein. Also, because it contains phytate, soy in a pet’s diet can actually impede the digestion and absorption of proteins and minerals in a dog or cat’s body. Cats especially do not need or benefit from soy, as they are obligate carnivores (they must eat an almost exclusively meat diet) and benefit very little from plant matter. And though dogs might better tolerate it, soy can be more of a harm than a help in their diet.

Soy also naturally contains phytoestrogens, plant estrogens that are documented endocrine disruptors in humans and can mimic estrogen in a dog or cat’s body. This can lead to issues like infertility, immune system issues, hair loss, and can block the enzymes needed to properly digest protein.

This may result in gassiness and bloat in dogs that in extreme cases can prove deadly. Additionally, soy has been linked to thyroid issues in dogs and cats, as well as seizures, and can be an allergy trigger.

All of the above is in addition to the likelihood that the soy in your pet’s food is a genetically modified soy (GMO) and that the intense processing of the plant in a north American factory has rendered it more toxic, as opposed to less.

The Bottom Line: While there is limited research in soy in a dog or cat’s diet, some studies have shown that long term feeding of soy can be detrimental to your dog or cat’s health. With the information available, based on some animals studies as well as human studies, soy is something we recommend avoiding in your pet’s food.

Corn Protein

No matter what pet food companies try to tell you, corn is not an equivalent source of protein to meat. Corn is almost exclusively used in pet food as an inexpensive way to make it more filling, raise (less bioavailable) protein levels, and to make (false) claims about improving your pet’s energy.

If you see corn as the first ingredient in your pet’s food (or as one of the first ingredients), you might want to consider another food.

Essentially, it is an inferior protein, not to mention an inferior ingredient overall.

Corn is often advertised as a highly digestible protein. But corn in and of itself is not easily digestible by mammals. It has to be highly processed to make it “highly digestible”. The more corn is processed, the higher its glycemic index goes up, often causing issues for dogs especially with sensitivities. Consumers also often equate highly digestible with “highly nutritious” which is simply incorrect, and corn is no exception.

On the scale of biological value eggs rank the highest at 100 and corn gets a 54 – well behind beef and fish meal at 78 and 92 respectively. Furthermore, corn’s “Completeness Score” on the USDA’s National Nutrient Database for Standard Reference, corn scores a 34 unlike spinach which gets a 91.

Lastly, when it’s claimed that corn is a superior protein on par with meat, that is also simply not true. Not only is corn not as usable a protein, it can in no way compete with meat as a means of energy. Corn may be fat free, but cats and dogs need fat (which meat has) to have energy. To have energy, an animal also needs an appropriate amount of calories from their protein.

Corn meal (protein) has 4.0 Calories/GM whereas beef has 7.3 Calories/GM and chicken has 6.3 Calories/GM. Obviously corn does not compete.

The Bottom Line: Corn has some nutritional value, but is no replacement for meat. It is generally a filler that the pet food industry isn’t always honest about. Will it harm your otherwise healthy pet? Probably not. Will it nurture them? Probably not. However, if it’s in your dog or cat’s food, best for it to be lower down on the list and definitely not one of the major sources of protein.

Potato Protein

Potato protein is problematic for many of the same reasons as listed above: it is not as biologically available as animal protein, it is not always easily digestible to dogs or cats, it is often used as filler, and it converts quickly to glucose (sugar) which can lead to inflammation. Though potatoes are not a grain, they can often counteract the benefits of a grain free diet (due to glucose production).

Potato protein is a heavily processed byproduct and is used to increase protein in pet foods and as filler. Nutritionally the benefits are modest.

The Bottom Line: Potatoes in your dog’s food are OK. Less so in your cat’s food. Will it harm an otherwise healthy pet? Probably not. Could it exacerbate an underlying issue? Possibly. Is it a quality source of protein? No. Some pets may do great on some potato protein (or potatoes for that matter) others may not. That’s a decision you must make. But as a main source of protein, potatoes can never replace meat.

Pea Protein

Ah, the trendy pea protein.

Pea protein has become very popular in dog and cat foods. Some premium pet foods will even boast their use of pea protein as an ingredient.

While peas do indeed contain a good amount of protein and are a good source of carbohydrates and fiber, they are not the “wonder plant protein” that some companies would have you believe. Peas, though perhaps a higher quality “filler” than soy, is still simply a way to increase protein in a less expensive manner than meat.

However popular pea protein is, do not forget that it is still a plant protein (a legume) and cannot replace animal protein in your dog or cat’s diet. That is, it is not a completely biologically available protein for your pet; they cannot fully utilize the protein in peas.

Additionally, many nutritionist have expressed concern over lectin proteins in peas (and frankly in most other plan proteins). Lectin proteins “are sticky, binding proteins” that bind to receptors that “regulate carbohydrates into glucose” and can lead to “diabetes, obesity, and cardiovascular disease.” These proteins can also bind to the vili in the intestines blocking nutritional absorption.

And like soy protein, pea protein also contains phytate.

The Bottom Line: Pea protein is not the worst plant protein that could be in your pet’s food. Some peas in your pet’s food are not a bad thing. What is more concerning is how ubiquitous they are; how readily the pet food industry seems to be leaning on them. No matter how much “better” it is than corn or soy, pea protein is still not equivalent to meat. Peas and pea protein in your pet’s food aren’t necessarily a bad thing. But once again, if pea protein is one of the first ingredients and a primary source of protein, you may want to reconsider your pet’s food.

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Don’t get us wrong, certain plant proteins or plant ingredients might not be a bad thing in your pet’s food. As a fiber, carbohydrate, or bolstering protein they can be a positive addition – especially if minimally processed.

But when all is said and done, your dog or cat will 99.9 percent of the time do better on a animal protein-based diet. That is just how their bodies work.

There is a balance to everything. Finding a balance in nutrition, palatability, and price that works for you and your pet is the eternal struggle of a caring pet parent. But the more you know, the better choices you can make.

We just endeavor to help you make those choices.

Wishing your furry family members yummy, tender (and healthful) vittles!

~Your Loyal Calvin & Susie Blogger