Are pet food fillers truly bad for your cat?

Q: What’s the best canned food to feed my cat? All the labels I’ve looked at are so confusing and full of fillers that I’ve gotten really frustrated. Even my veterinarian says he doesn’t know what to recommend. What do you suggest?

A: I hear it all the time. “That pet food is so bad. It’s full of fillers!" But what does that really mean? The truth is that there's no agreed upon definition for this common term in the veterinary literature. Here’s my working definition (based primarily on how veterinarians I know tend to apply the term): A filler is any lower quality, typically less expensive, usually bulky, starchy and carbohydrate-rich ingredient that could have been replaced by a higher quality, more biologically available one.

With that admittedly imperfect definition in mind, here’s how I try to tease out the fillers in pet food labels:

Start by reading the first few ingredients (Five is usually enough to take the pulse of a food.) They’re always listed in descending order of weight. So if beef is first and cornmeal is second, then there’s more beef, right?

Not so fast! Now you have to compare all of the ingredients on a level playing field by factoring out the water. Since beef is 70 percent water, whereas cornmeal is a dry product, there’s probably more corn than beef in this diet.

As if that wasn’t confusing enough, pet food manufacturers will also confound you by splitting the ingredients into several components so when you read the labels, you might think you’re getting more (or less) of an ingredient than you really are.

In this case, the cornmeal is probably what we'd traditionally consider the filler, since it stands in for the meatier ingredients we might expect in a cat food.

But here's the question: Are these filler-rich diets better than their meatier avatars? As long as they’re labeled “balanced and complete,” they may be every bit as good. We simply don’t know for sure. But given that cats have been eating these commercial diets for decades now with evident success, it’ll be hard to find a pet food company willing to part with its inexpensive ingredients. Nor will most pet owners elect to pay more.

Nonetheless, I agree with you on these points: a) Pet food labeling is often misleading and unfair to consumers. b) We don't know the true impact of so-called “fillers.” We simply haven’t studied them enough.

Dr. Patty Khuly has a veterinary practice at Sunset Animal Clinic in South Miami. Her website is Send questions to