Why Your Pet’s Diet Might Be Making Them Sick—and What It Can Teach Us About Our Own Diets

Our pets are very important to us. We want the best for them. Some of us can’t afford the most expensive or highest-quality pet food, but many of us still put real thought into what we buy.

The good news is that expensive does not necessarily mean better. We can make good choices with a basic understanding of nutrition and biology—but to do that, we have to put it in the context of evolution. In this article I’ll focus on mammals—dogs and cats specifically—because they have similar dietary requirements to each other and, in many ways, to us. We can learn something from them.

To keep an animal healthy, we have to consider what it has been eating in its natural environment—not just for thousands of years, but for tens of thousands of years. That’s how we understand what a species-appropriate diet is for a dog or a cat.

You can argue that domestication has changed them, and when you look at different breeds of dogs, that’s obvious. How did we get Chihuahuas from wolves? Selective breeding, that’s how. Cats are less changed than dogs. They’ve been domesticated for a much shorter time, and we had fewer specific jobs for them, so there was less reason to tamper with their genetics.

But even so, the amount of time these animals have been domesticated—roughly 15,000 years for dogs and 9,000 years for cats—is not enough time to significantly alter their dietary needs or allow them to thrive on a diet their species did not evolve eating. Evolution takes more time than that.

What Dogs and Cats Eat in the Wild (and Why It Matters)

I don’t think this is a big mystery. They ate animals—anything they could kill.

Wolves are pack hunters and can take down larger prey through cooperation: deer, elk, even cattle. Domestic cats are solo hunters (unlike their larger relatives) and prey on birds, rats, mice, and sometimes reptiles and insects. You can still watch them hunting today. Even indoor cats can be great mousers, though some are lazy and will just wait to be served cat food.

It’s important to note that wolves and cats will typically eat an animal nose to tail, often preferring the fattier parts like organ meat, which is loaded with essential fats and nutrients. Wolves will also break open bones and eat the marrow. Cats will swallow small rodents whole; the bones provide calcium and marrow and are not dangerous if they are raw. Bones only become brittle when they are cooked or dried out over time.

Notice I said essential fats. That’s because their bodies cannot manufacture what they get from taking in fat. They will die if they don’t get it. The same goes for protein. Both fat and protein are essential nutrients that our pets must have to be healthy. The same is true for Humans.

Do you know what is not an essential nutrient?

Carbohydrates.

Dogs and Cats- What Would they eat in the Wild?

Carbohydrates: The Non-Essential Nutrient

Carbohydrates break down into glucose in the bloodstream, which is basically starch/sugar. This spikes blood sugar and triggers the release of insulin. The insulin causes any glucose that is not burned immediately to be laid down and stored as fat.

Protein and fat, however, do not trigger the same insulin response, and do not lead directly to the creation of fat in the same way. The small amount of glucose the body actually needs can be created from protein by the liver, so carbohydrates are not an essential nutrient.

Fat and protein are essential. Dogs, cats, and humans would die without adequate fat and protein intake. And they will suffer disease without enough fat.

Overeating and Weight Gain Are Symptoms of the Wrong Diet

As mentioned above, adequate fat intake is essential for carnivorous animals. When an animal is eaten nose to tail, it contains the right balance of protein and fat. Many carnivores actually prefer organ meat and eat it first, because it’s fattier. They sense—by taste and feel—that this is the most substantial part of the animal.

Brains are among the fattiest parts of an animal. Our brains, for instance, are about 70% fat. Humans, just like dogs and cats, need plenty of fat in our diets for our brains to function properly—not to mention every cell membrane in our bodies. The high fat content of the brain is why cats often eat the heads of mice and rats and leave the body behind. Hunter-gatherer societies like the Inuit and the Plains Indians were known to favor organ meats and fatty cuts, giving the lean meat to the dogs.

This brings us to overeating. Animals on a species-appropriate diet generally don’t do it. Fat triggers hormones that signal the animal is full and satisfied. Carbohydrates do not. A carnivore will burn right through carbs, receive very little nutrition, and still feel hungry an hour or two later.

Fat and nutrient-dense foods like meat satisfy nutritional requirements and release satiety hormones that tell the animal it’s had enough. This is why we mostly see overweight animals when they have been eating a non–species-appropriate diet.

A cow does not overeat grass. If we want to fatten up a cow, we feed it wheat, soy, and/or corn. Likewise, if you want to fatten up a dog, cat, or a human for that matter, you would feed them the same. The difference is that cows eat grass, while dogs and cats eat meat.

The same goes for humans, because we are carnivores—not omnivores, as we have mistakenly believed for a very long time.

Starch Is a Slow Poison (and “Grain-Free” Can Be a Trap)

When my one-year-old cat developed a heart murmur, I was at a loss. Why would such a young cat—being fed “healthy” grain-free cat food—have health problems at all?

My vet suggested that I feed the cat some food with grains in it. When I looked up the association between heart problems and grain-free pet food, a bunch of stuff came up. Grain-free dog food had been shown to be associated with heart problems, and cat food was suspected, but there was not enough research on cats.

Scientists hypothesized that dogs have some need for grains that they would ingest by eating the stomachs of animals that eat grains. That sounded like a pretty large stretch to me. Instead of grasping for something like that, did they ever ask a simpler question?

What are they putting in grain-free pet food to replace the grains they are taking out?

Here is the thing: pet food—wet and dry—needs something to hold it together. Wheat and rice often do the job. But manufacturers figured out that if they could use legumes instead, they could hold the food together and raise the protein number on the label. They know dogs and cats have a high protein requirement, being carnivores, so this looks like a win-win.

The problem is that carnivores need to get protein from meat. They did not evolve to get it from legumes. And just because legumes raise the protein number on the label does not mean that protein will be bioavailable to your dog’s or cat’s system. Even worse, there may be consequences.

Everyone in every culture knows that most legumes need to be cooked properly. This is to break down plant toxins and anti-nutrients that the plant makes to protect itself. Most legumes are soaked for a day or two to remove as much of the toxic chemicals as possible, and many are cooked over a long period of time—sometimes even with the water changed halfway through, as with pinto beans.

Under cooked pinto beans are so toxic they can make you very sick or even kill you if not properly prepared. Other legumes may not have such an extreme effect, but still have quite a bit of toxic material that comes through even when well cooked.

These toxic substances— known as lectins and other anit-nutrients—attack your gut lining and can make you susceptible to digestive problems and even food allergies. On top of that, legumes contain a large amount of starch. Starch spikes blood sugar, and when eaten regularly with other substances that break down into glucose, it can contribute to metabolic disorders like type 2 diabetes, especially when grouped with other high-glycemic foods.

Do you think these food companies soak split peas, lentils, or garbanzo beans before prepping them for your pet food? Not only do they not soak them, they don’t even cook them. These beans are ground up raw—plant toxins, anti-nutrients, lectins and all—and put into pet food. That means a very high starch load, which is linked to all sorts of health problems, including an enlarged heart and arrhythmia.

My own cat’s heart murmur went away once I stopped feeding her grain-free cat food, on the advice of one of my vets. It worked, and it resolved in a matter of months.

The Food Industry Is Not Your Friend

If you think the food industry has your—or your pet’s—best interest in mind, I have news for you. At least half of the big food companies out there were bought by the tobacco industry once they were repeatedly sued and tobacco sales went down. They use the same manipulative marketing tactics with harmful substances in food as they did with cigarettes.

The big pet food companies that are doing research on how to formulate a healthy pet diet are really just going through the motions. You can use research to figure out an animal’s nutritional requirements, but if you try to fill those requirements with plant- and grain-based materials—materials that are basically leftovers from the human food-processing industry—you are going to be feeding pets food that fits the requirements on the label but does not offer a truly bioavailable source of nutrients.

More than that, you’re delivering plant toxins, anti-nutrients, and a high level of carbohydrates that no carnivore should be eating. And this really applies to humans as well.

Humans evolved to eat mammoths, not pasta. We can make use of grains and vegetables, but they are not particularly good for us. Almost every human disease that was once blamed on fat and cholesterol can now be blamed on sugar—refined sugar and carbohydrates, and even natural sugars and carbohydrates.

This is why human stature, bone density, and overall lifespan went down when humans settled down to farm. Not in thousands of years, not in hundreds—within a few generations. We have the fossil record to prove it. Ten thousand years of farming is not going to change two million years of evolution as a hunter-gatherer. And if you think ancient humans ate a significant amount of gathered fruits and vegetables, try eating only local, in-season for a while and see just how easy that is.

What to Feed (and What to Avoid)

Anything you feed your dog or cat that is not meat has the potential to harm them. Some of the food that is labeled as a healthier choice is the worst. High-glycemic vegetables like carrots and sweet potatoes may lead to diabetes, just like in humans.

Grains are not good, and the pesticides used for them are especially not good. But the legumes and other such nonsense put in your expensive “grain-free” pet food are particularly despicable.

Yes, no cat or dog should eat grains. Really, no human should either.

For humans: if it has an ingredient list, be suspicious. The longer the ingredient list, the more suspicious you should be. For dogs and cats, look for meat as the main ingredient—organ meat, meat by-products, all that stuff is fine. Humans would also do well to eat more organ meat, even bone meal.

You don’t necessarily need to buy the most expensive food to eat well. You just have to know what to look for and what to avoid. It is the same for our pets as it is for humans.