Talking about animal nutrition on this blog is like throwing rocks at a hornet’s nest. People tend to get riled up really fast. A few days ago I wrote a nutrition post that was designed to make people angry, and it worked as predicted (I also apologized for the post in the comments section). I feel like now I owe my readers a serious post on nutrition.
A note to commenters: since this is a serious post, I expect your comments to be sincere, thoughtful, and above all respectful to me and to your fellow readers. Comments that do not meet these requirements (as judged by me–it’s my blog) will be deleted.
What is nutrition?
Many people have strong opinions on the subject, but I don’t know how many people have truly thought the matter through. Let’s start with the basics.
Nutrition is the study of the body’s use of nutrients. The most common and important classes of nutrients are proteins, carbohydrates, fats, coenzymes (vitamins), and salts.
Proteins, carbohydrates, fats, coenzymes, and salts are chemicals. These chemicals can in many cases be broken down, modified, or synthesized through the body’s own chemical processes. The study of the body’s chemical processes is known as biochemistry. Nutrition is a subfield of biochemistry.
The fields of physiology and cell biology also are intertwined with nutrition. But in the end, nutrition always boils down to chemicals interacting with the body through biochemical processes.
It is not possible to understand nutrition without understanding cell biology, physiology, and especially biochemistry and chemistry. If you don’t understand chemistry, you don’t understand what happens to food once it’s past the mouth (or in the mouth, for that matter).
In other words, nutrition is chemistry.
Let’s use chemistry to answer one of the most incendiary questions in the animal blogosphere: does corn have nutritional value for cats and dogs?
A corn kernel consists of an outer envelope of cellulose. Inside the envelope are primarily carbohydrates and proteins.
Cellulose is indigestible by cats and dogs. It has no nutritional value. If corn is not ground or chewed, the proteins and carbohydrates inside the kernel cannot be accessed by the body.
If corn is ground, the inner parts of the kernel are accessible to the body. Cats and dogs produce enzymes that can break corn protein down to its constituent amino acids (building blocks). These constituent amino acids can be reassembled into other proteins; they also can be converted into energy, fats, and carbohydrates. Many of the carbohydrates in corn also are accessible for bodily metabolism.
This means that corn has nutritional value for cats and dogs.
Before you get mad, note this: although I said corn has nutritional value, I didn’t say that it necessarily should be a major ingredient in dog or especially cat food. Something can have nutritional value (a statement of hard fact) without necessarily being nutritious (a more judgemental term). I think it’s possible that the relative levels of carbohydrates in corn and the mix of amino acids in corn protein may not be appropriate for cats and dogs. There is room for debate on the matter of whether corn really belongs in pet food.
Now let’s consider beer. The ethanol and carbohydrates in beer can be converted to energy, other carbohydrates, and (as many middle-aged men know) intra-abdominal fat. Beer has nutritional value, but even I, as a serious beer lover, wouldn’t try to claim that it’s nutritious.
An understanding of biochemistry and physiology reveals that bodies are very versatile. An understanding of this versatility leads to the realization that animals can thrive on a pretty wide variety of foodstuffs.
An understanding of this versatility also lays waste to the biologically (or evolutionarily) appropriate arguments that are put forth by some proponents of certain types of pet food. These arguments, as I have heard them, state that animals should eat food that they evolved to eat.
The evolutionarily appropriate argument never passed the smell test for me. If it’s important for cats and dogs to eat evolutionarily appropriate food, then it should be important for people to eat evolutionarily appropriate food. Yet, outside of a few tribes in the Kalahari, remote Amazon, and other remote forests, almost no humans consume the hunter-gatherer diet that our species evolved to eat. Humans also routinely eat foodstuffs that were not present during our evolution. I just ate a cheese and tomato omelette with breakfast potatoes. The eggs were the only evolutionarily appropriate item on the plate, and even they were much different from eggs that my hunter-gatherer ancestors would have consumed. It was a healthy and nutritious meal nonetheless.
In the end it does not matter whether an individual’s diet is evolutionarily appropriate. What matters is whether it is complete and balanced.
There is room for a great deal of debate on whether commercial pet foods are complete and balanced.
My experience with tens of thousands of animals has left me with some opinions on commercial pet foods. Most high quality commercial dog foods seem fine to me. Dogs generally are living to ripe old ages and generally are not suffering from food-related illnesses (I know there are exceptions, but in this case I’m talking about the population at large).
Commercial cat foods, in my opinion, are a different story. More than half the cats I see are overweight or obese. Obesity-linked illnesses such as diabetes and arthritis are epidemic. Diet also may play a role in triggering hyperthyroidism, one of the most common diseases in cats. Finally, there is a clear correlation between diet and feline lower urinary tract disease and urinary obstruction.
I strongly hope that 20 years from now cat food formulations will be markedly improved and more healthy. Time will tell.
Beer photo by Steve Parker.