No corn, no soy, no wheat. Seems to be a near unanimous claim — from both pet food companies and self-help websites. According to Petfood Industry’s Dog and Cat Food Ingredient Database, soy is found in less than 13 percent of dog and 20 percent of cat foods. That is a long way from its once dominant position. Today it is vilified as a cheap filler, allergen and goitrogen, among other things. This seems somewhat surprising given soy products are a cornerstone for vegetarian and vegan dietary choices and the antithesis of animal proteins in the human foods market.
Soybean meal and its use in pet foods
Soybean meal is the predominant soy source in pet foods. There has been a wealth of research published with dogs and cats over the past 20 years in which it was the subject. Generally speaking, this research would support soybean meal in animal foods as wholesome, biologically available and commercially sustainable. So why the disconnect among research, commerce, the critics and the market? Is it merely that soybean meal is a co-product from the oil crush and relatively inexpensive compared to the rest of the proteins? Does it fail the “novelty” test for modern ingredients? Perhaps it is the wisdom of the masses, and there really are some problems with this ingredient? Some of the answers may be elusive, but let’s look a bit closer.
Soybean meal is relatively inexpensive compared to rabbit meal, venison meal or duck meal, but the volume of these more exotic proteins is quite small and very sporadic. It is hard to run a business on their intermittent availability. Even protein meals from peas and potatoes are difficult to procure on a regular basis. So a little mundane maybe, but soybean meal is consistently available and relatively sustainable. This constant supply is due in part to decades of intensive genetic selection and even genetic engineering to improve yields of soybeans. Increasing protein supply is essential if we’re to feed the nine billion people (and their pets) who will be inhabiting our planet in the next 30 years.
Beyond volume, soy proteins are relatively high quality compared to other plant-based sources. Soybean meal does lack adequate methionine for maximal animal performance, but it has a surplus of lysine, which serves as a great complement to cereals as a counter balance. Even LID (Limited Ingredient Diet) formulas rely on protein-carbohydrate pairs to work in concert. Said another way, pet foods are not single ingredients so we shouldn’t judge a single ingredient against the whole.
There are storage proteins in soy that can be immune-sensitizing; however, soybean protein is no more antigenic than any other plant-based protein. Peas and lentils are also members of the legume family with similar storage proteins — they aren’t somehow magically different regarding their diet hypersensitivity. Any protein can be antigenic under the right circumstances. Most of the literature would suggest that the animal-based proteins are more likely culprits than cereals and legumes.
There are also some bioactive proteins found in soy. Of most concern are the protease inhibitors (e.g., trypsin inhibitors) or the phytohemagglutinins (e.g., lectins). These are denatured (inactivated) by the cooking process. They are not an issue in conventional pet foods that have been extruded, baked or canned. They would only be of concern in a raw food diet.
Soybean meal also contains appreciable oligosaccharides like raffinose and stachyose. These non-structural polysaccharides can be good in moderation. We often describe some classes of these compounds as prebiotics. However, there is such a thing as too much of a good thing, which is certainly the case for the NSP found in soybean meal — if you want to avoid flatulence and soft stools. But are they bad for health? Certainly not; they are just a pet-parent nuisance. Most pet food companies use soybean meal in “judicious” quantities that don’t exceed what the dog or cat colonic fermentation can manage: generally, less than 12 percent of a formula.
Current research and other factors to consider
There is some recent work to suggest that soy contains phytoestrogens that may influence thyroid function in dogs and cats. Further, there have been some concerns expressed that phytoestrogens might affect reproduction and fecundity. While this is a distinct possibility, so too would other legume seeds like peas, faba beans, lentils, chickpeas and most of the beans. Further, the effect is dose-dependent, and the research data would suggest that the effective level is quite high and might only pertain to certain animal life stages. Finally, there are some suggestions that the differing metabolism in the dog and cat, relative to humans, may net some benefit to health and disease mitigation.
There are some other factors that we have to consider when formulating with soy, like mineral availability, palatability, etc., but these are generally addressed quite handily. While soybean meal hasn’t fared well in the press, it is a sustainable ingredient with a high-quality nutritional package from the formulator’s perspective. It has functionality in the production process, digestibility is high, and judicious use leads to good stools and no flatulence. It may not appeal to everyone, but it certainly is a blue-collar work-a-day ingredient that deserves to be used in pet foods where a “value” purpose can be served. Keep in mind that last year’s “facts” may become next year’s “fiction.” There is a great deal more to learn about soybean meal and the other soy ingredients in healthy, sustainable, economical pet foods.
Looking back: Why aren’t pet food manufacturers on the soy bandwagon?
Soy uncommon in dog and cat foods