Believe it or not, this post is going to seem a little fiddly. You might think it wouldn’t be so tough to spot a filler in a list of ingredients, but you’d be wrong.

Even after defining a filler in terms of biological appropriateness, bulkiness, ingredient quality, and expense, this issue offers no simple slam dunks. In fact, I’m kinda wishing I hadn’t waded into this morass right about now. In the process of writing these three posts, I’ve insulted people I didn’t mean to (I get so many e-mails a day, I didn’t know it was a Purina employee I was talking to!) and gotten my hackles up more than once (sorry again, SkeptVet).

So, you know, this is par for the course when it comes to pet food. Because nothing in my job as a pet health blogger gets everyone’s blood boiling faster than a heated debate on the issue of commercial pet food and animal nutrition. But that’s another post. For now, we’re going to clean up this trio of pet food entries on a constructive high note.

To that end, here’s what I want you to come away with after reading this: How you can read a bag of pet food to determine whether what you’re buying is a food replete with fillers instead of the high quality ingredients you would prefer.

It’s a tall order. After all, pet food companies know you read the labels. But they also know you’re not very good at it (nor are most veterinarians, if my first ten years in practice are any measure). Which is why a bit of tough slogging is ahead. So stay with me now!

To get you up to speed, here’s my working definition of the word "filler," when used in a sentence with the words "pet food": A lower-quality, typically less-expensive, usually bulky or carb-rich ingredient that could have been replaced by a higher quality, more biologically appropriate one.

With that in mind, here are my three steps to knowing what’s a filler and what’s not:

1. Read the first five ingredients on the side of the bag or can. They’re listed in descending order of weight as they’re added to the formula so that when "chicken" is the first ingredient in a dog food, "ground yellow corn" the second, and "corn gluten meal" the third, you can be sure that by weight, there’s more chicken than ground yellow corn, and more ground yellow corn than corn gluten meal.

The problem, however, is that these ingredients always include the weight of any water they might inherently carry. For example: "Chicken" is about seventy percent water (just like most fresh meat). But "ground yellow corn" is a dry product, and "corn gluten meal," by definition, has already been dehydrated and defatted. Which means that while chicken is the first ingredient on the list, this formula would have to have more than twice as much chicken, by volume, than ground yellow corn to come in first when all the ingredients are measured with the same amounts of their natural water.

It’s like comparing apples to oranges, I like to say. Unless all the ingredients are measured on a dry matter basis (a level playing field), I can’t say that there’s more chicken in this than corn unless you show me your recipe (which you won’t because the FDA says you’ve got a right to protect your "formula").

*Conclusion: In this case, corn meal and corn gluten are the fillers. The gluten might be a highly digestible protein source, but I’m sorry, I won’t pay $30 a bag for a glorified corn-based product. Not that there’s anything wrong with corn … but not when I’d rather feed my dog a more highly digestible, biologically appropriate protein — and certainly not when you’ve just suckered me into thinking I’m buying all those gorgeous meats and veggies pictured on the front of the bag.

2. Check for "splitting."
Yeah, I know the term sounds odd, but "splitting" is another way pet food manufacturers game the system to get you to believe their food’s higher in quality than it really is. What they’ll do is offer the same ingredient in several guises within the first five ingredients so you’ll believe you’re getting more (or less) of that ingredient than you really believe you are.

For example: One brand of canned cat food offers fish broth as the first ingredient, corn gluten meal as the second, fish as the third and animal fat preserved with ground yellow corn as the fourth. OK, so this essentially means flavored water is the first ingredient. But fish is in there, too, lest you doubt their seriousness in offering you a food fit for a carnivore. Still, it’s pretty obvious that when everything’s said and done, this is a corn-based product. (Reference my issues with corn, above.)

Not only is the pet food company playing apples and oranges with naturally hydrated and dehydrated ingredients, it’s splitting the fish into two parts (one seriously watered down) so it looks as if fish is a bigger part of the diet than it really is. Similarly, it’s splitting the corn ingredient into two parts (second and fourth behind fish) so that the corn actually looks like less of an ingredient.

*Conclusion: Corn products are, again, being used as fillers. Its nutrients (its high protein percentage, in particular) are being used to stand in place of the fish, protein-wise. Rest, assured, however, the product smells and tastes of fish.

(Lest anyone think I’m picking on corn, the same can be said for many of the grains in these cases. Grain proteins may be highly digestible but they’re not as biologically appropriate. What’s worse is reading label after label and becoming aware that a lack of clarity fuels the gamesmanship that is inherent to this labeling system.)

3. Check for higher quality proteins and carbs. Here’s the toughest part. Deciding what’s quality and what’s not can be highly subjective.

Still, some examples are easy. Take Old Roy for instance: ground yellow corn, soybean meal, ground whole wheat, corn syrup, and poultry fat. Yes, those are seriously its first five ingredients. And by my definition, every single one is a filler. Why? I don't think you could come up with a cheaper, less biologically appropriate way to feed a dog. It’s worse than Burger King. And yet when you calculate all the nutrients, it doesn’t lie. It "meets all your dog’s nutritional needs."

That is, if you have really low standards for what science shows our dogs can live on.

There are plenty of times when what I really expect to see on a bag of so-called super-premium pet food is a list of at least three high quality ingredients I can recognize in their natural form, and all I get are beef, soybean meal, ground sorghum, and poultry fat.

In these cases, I’m gratified to see beef at the top. Problem is, I’m pretty sure that more of the protein in this formulation is from the soybean meal, with only a little of the beef protein. So where’s the quality I’m paying for? Is it in the ingredients, or is it in the amazing ability of modern marketing to convince us that these diets are "natural" and "complete?"

Now that the system has gamed me so many times, I’m becoming aware that I’m a junkie for feeding my pets actual ingredients … not just nutrients sourced from vegetables and grains.

*Conclusion: How about some fish heads, sweet potatoes, barley, eggs, milk, soybeans, brown rice, corn (the real thing), carrots, beef hearts, and chicken livers? Throw me a bone. Tell me I’m feeding my pet something real. Because when it comes to the top ingredients in my pets’ food, anything that doesn’t seem real, anything that reads like I’m feeding my pet a "nutrient" instead of an actual foodstuff I recognize, or anything that leads me to suspect I’m being marketed to … that’s a filler in my book.

And that’s my biggest problem with fillers. They’re hard to define … and even harder to explain. And while you may disagree with me on what constitutes a filler and what’s best for our pets, one thing should be obvious to anyone who just slogged through this post: Reading a label on a bag of pet food should NOT be like playing Sudoku.

Dr. Patty Khuly

Art of the day: "Sudoku Fever" by Buntekuh