For most of human history, dogs ate scraps, leftovers, or such bits of animal carcasses as were considered unfit for human consumption. These days, of course, we can walk into any grocery or pet store and find aisles filled with every kind and variety of dry and wet food imaginable. It’s easy to forget that, as a concept, dog food has only existed for the last 150 years. Pet nutrition has come a long way since then, evidenced by the sheer range and availability of specially formulated comestibles for every size and age of canine.

Why is it then that we come home from work and find our dogs rooting through the garbage? Why do dogs eat wacky things like dirt, grass, or even their own poop? And why, in the name of all that we hold sacred, do our dogs seem to take special satisfaction in eating cat food? When we find our dog’s face buried in the cat bowl, it’s commendable to wonder if these proclivities are normal or even healthy. Can dogs eat cat food safely? Should they? Let’s examine the factors involved and the risks.

Why do dogs eat cat food?

This question has two answers, one more practical than the other. As you may know, over the course of their evolution, both in the wild and as domestic pets, dogs have proven themselves to be proficient hunters, foragers, and scavengers. They are opportunistic omnivores, meaning that they can turn to a wide and surprising range of foodstuffs, either for nutritional or digestive value. Dogs eat cat food because it is there, it is different than what they’re accustomed to, and because it presumably tastes good.

The other, less satisfying, reason is that dogs are indiscriminate eaters. Seeing a dog eat grass or rocks may leave dog owners scratching their heads, but it’s no less true for all that. A dog’s senses of smell and taste combine to provide their most comprehensive ways of understanding and experiencing the world. Canine curiosity means that they’re equally likely to devour a foreign object as a high-quality dog food. A dog who eats socks, for example, takes no benefit from the experience, and may even suffer blockages in the digestive tract as a result, but he does it anyway.

Dogs and cats have distinct nutritional needs

One consequence of being an omnivore is that a dog’s nutritional requirements are much more varied than those of cats. The content ratios that a given dog needs — of proteins to fats, of fats to carbohydrates, and so on — vary based on factors like age, size, and breed or mix, but it is safe to say that a healthy dog’s diet should encompass the whole spectrum of nutrients, and that protein should be less than 20 percent of their daily intake. Fats, while necessary, should be doled out at even smaller portions, making up somewhere between 10 percent and 15 percent of a meal. Dogs also need more of the fiber found in carbohydrates than cats do. A quality dog food should take a dog’s specific dietary needs into account.

Cats, on the other hand, thrive on food rich in fats and proteins derived from meat. These nutrients comprise much of the content in store-bought cat food. Dry cat food also contains some plant or vegetable matter, mostly for the sake of kibble cohesion and integrity. Wet canned cat food, on the other hand, has a great deal of water as well, which, combined with a high concentration of meat-based nutrients, provides a typical cat exactly what she needs. Why do dogs like cat food? Probably because its contents are different enough from what they normally eat that it has the attraction of novelty.

Is wet or dry cat food worse for dogs?

While dogs will eat almost anything if the situation presents itself, their digestive system is as habitual as ours. If a dog eats wet or dry cat food for the first time, there’s always the risk of digestive upset, either in the form of vomit or diarrhea. Whether it’s cat food or dog food, dry kibble tends to have a higher concentration of carbohydrates. The tendency for people to feed their pets dry food exclusively is one of the main reasons why so many dogs and cats are overweight. Neither wet nor dry cat food, if they consume it once, or only occasionally, poses any inherent danger for dogs. Should it become habitual, dry cat food is much worse for a dog’s overall health and functioning.

Should dogs eat cat food regularly?

There’s no question that dogs can and do eat cat food, both dry and wet, for both a variety of reasons and simply because it is there. A better question, and one we’ve not looked at yet, is whether dogs should eat cat food. We know about the high protein and fat content of cat food. We also know that a dog has more widely distributed nutritional requirements. If a dog is eating cat food exclusively, or on a regular basis, they will be getting far more meat proteins and fats than they strictly need. What are the risks if a dog is consuming cat food every day?

Obviously, if your dog is getting into the cat food, you’re going to have to buy more of it more frequently. That’s bad for your domestic economy. There are health risks for the dog in question as well. Fats are good for dogs and necessary for the best coat and skin health, but dogs need even less total fats in their diet than they do proteins. Dogs need proteins, but not at the level that they’re present in cat food.

What health risks are associated with cat food?

Cat food’s high concentration of both fats and proteins poses real danger to dogs if they eat it normally or exclusively. Protein is good for a dog in proper measure. Too much protein can lead not only to obesity, but also puts excessive strain on a dog’s kidneys and liver. Excess consumption of fats is just as problematic. Too much fat can negatively affect a dog’s pancreas, leading to pancreatitis, which can impact the efficiency of their digestion.

If it seems like your dog is addicted to cat food, you have a couple of alternatives. First is to restrict their access. If necessary, feed your cats in a room or area of the house where the dog is not allowed. One of the common conjectures or misapprehensions about why dogs eat things like grass or dirt is that they are making up for nutritional deficiencies. It’s worth consulting a veterinarian to determine whether protein or fat is lacking in your dog’s diet and adjust accordingly.

About the author: Melvin Peña trained as a scholar and teacher of 18th-century British literature before turning his research and writing skills to puppies and kittens. He enjoys making art, hiking, and concert-going, as well as dazzling crowds with operatic karaoke performances. He has a one-year-old female Bluetick Coonhound mix named Idris, and his online life is conveniently encapsulated here.