The difference between hypoallergenic and anallergenic pet foods is subtle but important. The Greek prefix hypo- means “lacking” or “less.” Hence, someone who is hypothermic is lacking in heat, and someone who is hypoglycemic has less blood glucose than they should. The prefix a- (or an- when it proceeds a word that starts with a vowel) is also Greek but means “no,” “not,” or “absence of.” We see this in terms like apolitical (not political) or anorexia (absence of appetite). Thus, hypoallergenic dog food contains fewer allergens, whereas anallergenic dog food contains none (or as close to none as possible).
What does that actually mean for pet food? Well, for most cats and dogs, proteins are the primary allergen, so hypoallergenic foods tend to use partially hydrolyzed proteins or proteins that have been broken down into smaller pieces and are therefore less likely to be recognized by an animal’s immune system, triggering a reaction. They tend to use a single source of protein instead of a blend and a single source of carbohydrates. Hypoallergenic pet foods often avoid the most common allergens for cats or dogs, sometimes employing specific parts of these animals—hydrolyzed chicken liver is common—or novel and “weird” protein sources like kangaroo, rabbit, or soybeans.
The problem is that roughly 25-50% of dogs will still have allergic reactions when fed hydrolyzed diets derived from proteins they’re allergic to. This may be due to incomplete hydrolyzation, leaving protein fragments still big enough to be recognized by the immune system, or even just cross-contamination from some part of the manufacturing process. For dogs like this, veterinarians often turn to anallergenic diets.
Proteins are long chains of amino acids. Their mass is measured in a unit called a Dalton (Da), or more commonly, a kilo-Dalton (kDa) because scientists prefer working with smaller numbers whenever possible. Protein masses can vary widely. For example, insulin has a mass of roughly 5.8 kDa, whereas ATP synthase, the enzyme responsible for powering everything we do, has a mass close to 600 kDa. Alcohol dehydrogenase, the enzyme that processes any alcohol we drink, weighs roughly 170 kDa.
There isn’t a consensus on how big a protein needs to be to potentially trigger an immune response, but we can confidently say that the smaller the protein, the lesser the chance. Hypoallergenic dog food tends to have proteins in the 3-15 kDa range. Conversely, Royal Canin’s Anallergenic food—debuted in 2012 after over a decade of research—was the first pet food considered to contain extensively hydrolyzed proteins. It contains proteins that are 95% less than 1 kDa and 88% broken down to the level of single amino acids!
In one randomized, double-blind crossover study of 10 dogs with cutaneous adverse food reactions, the Royal Canina Anallergenic diet did not trigger an allergy flare-up in a single participant. In contrast, a hydrolyzed chicken liver diet (a typical protein source for hypoallergenic dog foods) triggered a flare-up in 40%.
Despite being a feat of scientific engineering designed to help dogs and cats get relief from a condition without many other treatments, there remains a degree of controversy around Royal Canin’s Anallergenic food. Why? Because its protein source is hydrolyzed poultry feathers.
Pet food marketing has long relied on messages about feeding your dog as you would the other members of your family or avoiding “filler” ingredients. Unfortunately, this has resulted in demonizing ingredients like corn meal or hydrolyzed poultry feathers, even when all science supports their inclusion. Despite appeal-to-nature infused commercials referring to domestic dogs as “wolves” or “carnivores,” your Shih Tzu has evolved quite a bit from her wolf days and has different dietary requirements.
Dogs are not carnivores and haven’t been for thousands of years. They can digest grains quite well and benefit significantly from modern advancements in food processing, just like humans. Raw diets are dangerous for a multitude of reasons, and just because you wouldn’t want to eat an ingredient like hydrolyzed poultry feathers doesn’t mean it isn’t perfectly beneficial to your pet. Not to mention, as the poultry feathers are so extensively broken down before being included in kibble, it makes about as much sense to consider them feathers as you’d consider a single brick a cathedral.
All of the dogs in the above-mentioned crossover study readily ate the feather-based food, and such diets seem acceptable even for the more traditionally discerning cats. Despite claims to the contrary, hydrolyzed poultry feathers are well-digested by both cats and dogs.
Other attempts to demonize poultry feathers as a source of protein rely on characterizing them as a “waste product” of human meat processing—as if that’s a bad thing. For sustainability purposes, utilizing every part of an animal is far preferable to disposing of a perfectly functional ingredient. Claims that Royal Canin is only using feathers to benefit their own pockets are equally nonsensical, given how expensive the extensive hydrolyzation process is, the extensive research and development funding that went into perfecting it, and how much cheaper it would be to continue to use the conventional protein sources they already have.
Anallergenic food is a powerful tool for veterinarians and pet owners to diagnose and treat severe pet allergies that, prior to its invention, often had no great treatments. The demonization of by-products, highly processed ingredients, or whatever else you want to call hydrolyzed poultry feathers is unscientific rubbish that will almost certainly lead to pets who would benefit from this food not getting it. It’s high time we overcame our fear of the unknown and instead marvelled at how science can find unique new solutions to age-old problems.