Pet diet fads — what does real science say about it?


The New York Times posted an article about pet diet fads where humans are pushing food fads, like paleo, vegan, and gluten-free, onto their dogs and cats. These diet fads betray the pet owner’s lack of knowledge about the evolution and physiology of their pets, which can be dangerous.

I could argue all day with the devotees of these diet fads, but it’s frustrating. People who believe in their diets often act like religious zealots unwilling to discuss actual evidence supporting their nonsense. I mean gluten-free diets are just for people who have celiac disease, it’s not going to mean anything to those who lack that particular condition.

I’m going to focus on dogs and cats for this article because I’m just not an expert on avian dinosaur diets. I hope what you feed your favorite dinosaur, whether a parrot or parakeet, is appropriate. Since they prefer nuts, they’re already living with a paleo diet.

So, let’s talk about cat and dog diets. And why pet diet fads may be the worst thing for pets.

Photo by James Barker on Unsplash

Dog nutrition

Before we can get into what diet is appropriate for dogs, we need to discuss the evolutionary history of dogs, because their dietary needs became closely linked to human diets. We seem to think of dogs as being domesticated wolves, but even though that’s somewhat true, modern wolves and modern dogs are very different, especially when it comes to diet.

According to modern research, dogs and an extinct Late Pleistocene wolf diverged about as recently as 10-15 thousand years ago, although there is some evidence that dogs were domesticated up to 40 thousand years ago. That extinct wolf evolved into domesticated dogs, the modern grey wolf, and some related taxa, such as jackals and coyotes.

They are all in the same genus, Canis. The grey wolf and domestic dog are genetically similar because of cross-breeding, either accidentally or intentionally. 

Domesticated dogs co-evolved with modern humans, as humans moved from a hunter-gatherer society to agricultural. This is important because domesticated dogs eventually evolved to eat human foods. Domestic dogs have different dietary needs than wolves, because of co-evolution with modern humans.

All canids have a gene, AMY2B (Alpha-Amylase 2B), that codes for a protein that assists with the first step in the digestion of dietary carbohydrates. Wolves have only two copies of that gene, whereas dogs have substantially more copies of the gene. This gives domestic dogs a better ability to exploit carbohydrate-rich diets as they fed on agricultural products and waste in early human history.

Furthermore, an analysis of the dog versus the wolf genome shows that the dog has more genes that code for enzymes to process lipids, probably as a result of early human hunter-gatherers leaving lots of meat scraps. The dog diet, and its ability to metabolize it evolved as human food supplies changed over thousands of years. 

Domestic dogs evolved to consume human foods. They moved from an almost obligate carnivore (an animal that requires consuming meat to survive) to a slightly carnivorous omnivore.

This leads us to some of the issues with gluten-free, grain-free, or vegan diets. For example, dilated cardiomyopathy, or DCM, (the link is to the human disease, but the signs, symptoms, and pathophysiology are the same in dogs) is a condition in which the heart becomes enlarged and cannot pump blood effectively. According to an article from the Clinical Nutrition Service of Tufts University Cummings Veterinary Center:

DCM is a serious disease of the heart muscle which causes the heart to beat more weakly and to enlarge. DCM can result in abnormal heart rhythms, congestive heart failure (a build-up of fluid in the lungs or abdomen), or sudden death. In dogs, it typically occurs in large- and giant-breeds, such as Doberman pinschers, Boxers, Irish Wolfhounds, and Great Danes, where it is thought to have a genetic component. Recently, some veterinary cardiologists have been reporting increased rates of DCM in dogs – in both the typical breeds and in breeds not usually associated with DCM, such as Miniature Schnauzers or French Bulldogs. There is suspicion that the disease is associated with eating boutique or grain-free diets, with some of the dogs improving when their diets are changed.

So, is this latest rash of DCM caused by taurine deficiency? Most of these affected dogs were eating boutique, grain-free, or exotic ingredient diets. Some of the dogs had low taurine levels and improved with taurine supplementation. But even some of those dogs that were not taurine deficient improved with taurine supplementation and diet change. Fortunately, cardiologists reported the issue to the FDA which is currently investigating this issue.

Moreover, taurine deficiency, which is caused by the lack of this important amino acid in the diet of domesticated dogs and cats, results from a lack of meat in the diet.

The science backs up the fact that domestic dogs require a diet that contains both meat and grains, something that is lacking in most human fad diets. Most of the owners that pushed these pet diet fads on their poor dogs use anecdotes, not real science, to proclaim how great these diets are. Anecdotes are powerful, but they aren’t scientific data.

A dog will eat anything placed in front of them, they’re not smart enough to tell you that their heart might be enlargening. Or that they’re not getting an amino acid necessary for them to produce proteins necessary for the dog to survive.

Photo by Jeanie de Klerk on Unsplash

Cat nutrition

The evolution of domestic cats is quite different than the natural history of domestic dogs. Cats were domesticated from African wildcats around 9-10 thousand years ago. Like dogs, this occurred when human society moved from a hunter-gatherer to an agricultural society around this time. Domestic cats were valuable to early farmers to keep down the populations of vermin like rats and mice.

Unlike dogs, the artificial selection of domestic cats has not resulted in major genetic changes between domestic cats and their wild ancestors. Generally, the major change between domestic and wild cats is behavior, where the domestic cat is much more docile than the wild version. Of course, humans artificially selected for different phenotypes in cats that have led to the numerous breeds of cats (along with the proliferation of numerous deleterious genes).

Despite this domestication, cats retain behavior and physiology that allow them to live separately from humans. Thus, they remain obligate carnivores, and, unlike domesticated dogs, they have not become adapted to the more omnivore diet of humans. Domestic cats have evolved to consume raw flesh to meet their nutritional requirements to survive.

Feeding anything but a high meat diet to cats can be dangerous. I am not a fan of kibble for my cats, because that’s not what they evolved to eat.

All felids, that is, all cats including our pets, require a diet of animal flesh and organs. Much of the behavior of cats is related to predation, hunting, and killing smaller animals, such as rodents and birds.

Cats also have higher protein requirements than dogs – the cat physiology is incapable of synthesizing various essential nutrients such as retinol, arginine, taurine, and arachidonic acid. To get enough of these nutrients to maintain their health, they need to consume almost pure meat in their diets. 

But it’s more than just nutrients. The digestive systems of cats have evolved to eat raw flesh. As a result, Felids have the shortest digestive tract to body size ratio of nearly any mammal.

So fad diets like vegan diets are simply dangerous for them. And again, if a cat could talk to us, they’d be saying, “we want meat.”

Pet diet fads

Let’s look at some of the top pet diet fads and how they might help or hurt your pets.

Paleo diet — this diet is based on the myth that early humans had a particular diet high in animal meat, roots, fruits, vegetables, and nuts. It excludes grains, legumes, sugars, and “processed” food. I could argue all day long about what ancient humans ate, and it varied between the time of the year and location. Plus grains have been a part of human history since early hunter-gatherers. Nevertheless, because this diet lacks grains, it would be bad for your dogs. Cats would love the meat. Also, some of the fruits, vegetables, or nuts could be detrimental to your pets.

Vegan diet — although it is possible to supplement this diet with additional amino acids to replace those that would come from meat, we don’t know what else is in a typical carnivore diet that might be necessary for the health of our pets. And this is inappropriate for a cat since they are obligate carnivores and their whole nutritional physiology is built to consume and digest meat. And although we can’t speak to our cats and dogs, I wonder how happy they are lacking meat in their diet. If you think that being vegan is some magical power doesn’t mean your pets subscribe to that belief. And their health may suffer, despite your anecdotes.

Gluten-free — well, I contend cats should get grains in their diet, so maybe that would be good for them. On the other hand, dogs require grains like wheat, which is filled with gluten. So, it’s an OK idea for cats, but what a waste of time. And it’s a bad idea for dogs.

Raw diet — this pet diet fad was started a few years ago by people who think that the problem with our pets is processed food. The problem with it, as explained in the New York Times article, “In recent years, the Food and Drug Administration, the Centers for Disease Control, the American Veterinary Medical Association and the American Animal Hospital Association have denounced the diet as dangerous, citing the risk that some raw food may be contaminated with harmful bacteria.” And there’s no scientific evidence supporting health claims for this diet.

But the major problem with all of these pet diet fads is that there is just no robust, repeated, and reliable evidence that their pets are healthier on these diets. The supporter of these diets like to pull out the old conspiracy theories that veterinarians are supported by Big Pet Food (where have I heard this before?), so they dismiss these diets.

And advertising and online commentary seem to use classist language to shame pet owners. In other words, if you’re not feeding your pets these fad diets, you must be doing something wrong. Apparently, there are holistic veterinarians (who employ pseudosciences like homeopathy and acupuncture) who push these fad diets. I bet they’re anti-vaccine too.

But let me re-emphasize my basic point. There is no scientific evidence that these diets are any better for dogs, cats, and to be completely honest, for humans too. Well, a human would never eat a raw diet, that would be seriously dangerous.

I know you want to think of your pets as part of your family, and if you’re a vegan or paleo diet person, you want your pets to share in your beliefs. But, stop for a minute, and look at the science. Dogs and cats require diets based not on your beliefs, but their evolution as our pets.

Cats are carnivores. They want to eat mice and birds and fish. Dogs are omnivores who need a mixture of meats and grains to be healthy.

Don’t listen to anecdotes and testimonials (something we always say to those who want to believe in something on the internet). You see claims that a dog is healthier on the raw diet, but do you ever see the person who saw their dog sent to the veterinary hospital hooked up to IV antibiotics because of food poisoning? I doubt it.

Should you spend a little time considering your pet’s diet? Sure. I think cats should be on a nearly pure meat diet (cooked preferably). Cats get most of their water from food, and meat is about 70% water.

Dogs need a mixed diet, worthy of an omnivore. They need a lot of meat, some grains, and other table scraps. I suppose you could put a dog on a purely vegan diet, but it would take some hard work, and your vet should closely monitor the health of your dog. But your dog would probably be mentally happier (if that’s a thing) with a bunch of meat in their diet.

I don’t get food fads in humans. But I really don’t get trying to force these fads on our pets. They don’t deserve it. But if science shows us that one of these diets, or a new one in the future, is good for our cats and dogs, I’ll be all over that. I hope it’s forthcoming.

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