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Why Is This Potentially Deadly Item Found in 'Healthy' Pet Food?


Story at-a-glance -

  • Big pet food is on a “promote soy ingredients” kick these days
  • A recent pet food industry journal article tries hard to convince its audience that soybean hulls are a “quality fiber source” for dogs and cats
  • Soy products are used in pet food as cheap fillers; they’re also allergenic, genetically modified (in the U.S.), contain anti-nutrients, are biologically inappropriate for pets and have been linked to a variety of diseases in dogs and cats as well
  • If your pet isn’t getting enough dietary fiber, there are many safe, natural foods and supplements you can add to your dog’s or cat’s meals to boost the fiber content

By Dr. Karen Shaw Becker

A pet food industry journal headline asks the question:

"Soybean hulls: filler or quality fiber source for dogs and cats?"1

The author of the article quickly answers his own (apparently rhetorical) question with the subhead, "Soybean hulls are a good source of insoluble fiber and cellulose for the dog and cat diet." Needless to say, I disagree. Interestingly, so does processed pet food manufacturer Canidae, which includes soybean hulls on its list of nine pet food fillers to avoid:

"These are by-products of soybeans used in human food processing and are commonly known as 'floor sweepings.' Composed of skins and bean product that stick to the skins, they have little nutritional value."2

They are actually much worse than Canidae describes — more about that shortly.

Big Pet Food Is Really Pushing Soy Products Lately

The author kicks off his article by stating in the first sentence that, "High-fiber ingredients are often added to pet foods for the benefit of the animal." Again, I disagree. High-fiber ingredients, which are inexpensive and plentiful, are added to pet foods for the benefit of pet food manufacturers. As Canidae points out, soybean byproducts provide little nutritional value to dogs and cats.

The author goes on to lament that many "well-intentioned 'experts' or bloggers online" are misleading consumers when they disparage ingredients such as beet pulp, rice and wheat bran, and tomato pomace by calling them "fillers." He's concerned that animals may be short-changed if pet parents avoid formulas containing these ingredients. His logic escapes me. How is it possible to short-change dogs and cats by not feeding them cheap, biologically inappropriate ingredients?

The author thinks the reputation of soybean hulls has suffered more than other fibers, because not only is it called a cheap filler (it is), but it also "gets accused" of being an allergenic ingredient (it is) and a byproduct (it is). In addition, some pet food companies actually use the lack of soybean hulls in their formulas as a marketing tool, because they realize it's a cheap filler and many consumers don't want to see it in the pet food they buy.

According to the author, soybean hulls "can be a quality fiber source in a well-balanced dog or cat food." The author is putting the proverbial lipstick on a pig. A pig with lipstick is still a pig. If soybean hulls were such a nutritious "quality" ingredient in diets for dogs and cats, it doesn't seem the pet food industry would need to work so hard to convince us.

The Truth About Soy and Soy Products

Soy is a boon for processed pet food manufacturers because it's inexpensive and in constant supply, thanks to decades of intensive genetic selection and genetic engineering to improve yields.

In addition, soy is higher in protein than many other plants used in commercial pet foods, and even though it's a biologically inappropriate type of protein for dogs and cats, pet food manufacturers include it in their crude protein percentages on the guaranteed analysis printed on pet food labels.

Plant estrogens, also called phytoestrogens, produce biological effects in humans. In soy protein, the most common of these compounds are isoflavones. The way soy is processed affects the level of phytoestrogens. Traditional fermentation reduces the levels of isoflavones dramatically, however, factory processing (as occurs in the U.S.) does not.

U.S. varieties of soy are manipulated to be pest-resistant (soybeans have some of the highest concentrations of pesticides of any crop), with the result that they contain higher levels of isoflavones than soy grown in Japan or China. Raw, mature soybeans contain not only phytoestrogens, but also phytates that prevent mineral absorption and substances that block the enzymes needed to digest protein. Soy also contains other anti-nutrients, including:

  • Antigens in the form of non-denatured proteins that can create serious allergic reactions in both animals and people
  • Trypsin inhibitors that hinder the action of proteolytic enzymes in the GI tract, reducing the digestibility of proteins
  • Oligosaccharides — indigestible sugars that can cause gassiness and diarrhea
  • Phytic acid, which can interfere with the body's use of vital minerals like calcium, magnesium, iron and zinc
Click here to find out Dr. Becker's 20 Pet Tips for a Healthy 2020Click here to find out Dr. Becker's 20 Pet Tips for a Healthy 2020

Why Soy Is Poor Nutrition for Cats and Dogs

Soybeans and soybean-related products can be found in a variety of processed pet food formulas, dry, semi-moist and wet, as well as veterinary formulas and prescription diets. Because plant proteins are less expensive than meat proteins, as I've already mentioned, pet food manufacturers use them to increase profit margins.

The ingredient label might not even say soy, as it's commonly listed as vegeta­ble broth, textured vegetable protein or TVP, and perhaps other aliases. Pet nutrition experts agree soy isn't good nutrition for cats or dogs. It's considered a low-quality, incomplete protein well known to create food allergies and potentially much worse in pets. According to Sally Fallon and Mary G. Enig, Ph.D., authors of "Cinderella's Dark Side:"

"The soybean contains large quantities of natural toxins or 'antinutrients.' First among them are potent enzyme inhibitors that block the action of trypsin and other enzymes needed for protein digestion. These inhibitors are large, tightly folded proteins that are not completely deactivated during ordinary cooking. They can produce serious gastric distress, reduced protein digestion and chronic deficiencies in amino acid uptake.

In test animals, diets high in trypsin inhibitors cause enlargement and pathological conditions of the pancreas, including cancer. Soybeans also contain haemagglutinin, a clot-promoting substance that causes red blood cells to clump together. Trypsin inhibitors and haemagglutinin are growth inhibitors."

A 2004 study at the University of Pennsylvania looked at the amount of phytoestrogens in 24 commercial dog foods. Results revealed all the foods containing soy ingredients had concentrations of phytoestrogens in large enough quantities to have a biological effect on the pet.3

Soy has been linked to gas and deadly bloat in dogs. It's high in purines, making it a completely inappropriate protein source for urate-forming dogs. It's also high in silicates and promotes the formation of silica stones.

The carbohydrate action of soy can cause a rise in blood sugar in cats. Soy is also linked to thyroid damage, and hypothyroidism is already an epidemic endocrine problem in dog populations. The ingestion of soybean products may also be linked, either directly or indirectly, to seizures in both dogs and cats.

All this and more is why I recommend avoiding pet foods containing soy products. The potential risks associated with feeding soy are unacceptably high, especially when you consider your carnivorous cat or dog receives a much higher level of nutrition from animal protein sources.

How to Ensure Your Pet Is Getting the Right Amount of the Right Kind of Fiber

The only fiber wild dogs and cats ingest is whatever is found in the already-digested stomach contents of their prey, and, of course, the fur, skin, feathers, tendons and ligaments they might ingest from eating whole prey.

Although the amount of fiber found in the diet of wild dogs and cats is small, it serves a very important role. Likewise, dogs and cats fed processed commercial diets benefit from the addition of a small amount of the right kind of fiber as well. Our goal when feeding raw food diets to pets is to mimic the gastrointestinal (GI) contents that would naturally be found in their prey.

A fiber-deficient diet can cause diarrhea or constipation in both dogs and cats, but when pets consume unnecessary fillers, like wads of fiber, it inhibits digestion and absorption of many vital nutrients. A small amount of fiber is very important, but a diet loaded with fiber is very detrimental.

If you're feeding your dog or cat a nutritionally balanced, species-appropriate diet with appropriate supplementation, including a high-quality pet probiotic and digestive enzymes, and your pet is easily producing small, firm stools, she's getting the exact amount of fiber she needs.

As I mentioned earlier, in the wild, dogs and cats get to choose how much skin, hair and GI contents they consume with each prey animal they catch, but this isn't true of pets living in our homes. Good replacement options for your four-legged companion include:

  • Psyllium husk powder — 1/2 teaspoon per 10 pounds of body weight one to two times daily on food
  • Ground dark green leafy veggies — 1 teaspoon per 10 pounds of body weight one to two times daily with food
  • Canned 100 percent pumpkin — 1 teaspoon per 10 pounds of body weight one to two times daily on food
  • Acacia fiber — 1/8 teaspoon per 10 pounds of body weight one to two times daily as prebiotic fiber
  • Ground hemp seeds — 1/2 teaspoon per 10 pounds of body weight one to two times daily