I hear it all the time: "That pet food is so low quality. It's full of fillers!" But what does that mean, really?
To be honest, there's no agreed-upon definition for "fillers" in veterinary nutrition literature, so my working definition of the word (based on the common connotation) will have to suffice:
A filler is any lower-quality, typically less-expensive, usually bulky, starchy and carb-rich ingredient that could have been replaced by a higher quality, more biologically available one.
With that admittedly imperfect definition in mind, here are my three steps to knowing what’s a filler and what’s not so that you can start learning to decipher pet food labels for yourself:
#1 Check out the first few ingredients
It's crucial to know what ingredients go into your pet's food, right? But how do you figure that out?
Start by reading the first few ingredients on the side of the bag or can (five is usually enough). They’re always listed in descending order of weight as they’re added to the formula. So it is 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.
#2 Factor out the water
The problem, however, is that the ingredients listed on the side of a bag or can always include the weight of any water they might inherently carry. For example: "Chicken" is about seventy percent water (just like most fresh meat). Meanwhile, "ground yellow corn" is a dry product, and "corn gluten meal," by definition, has already been dehydrated and defatted.
All of this suggests that while chicken is the first ingredient on the list, this formula would have to have a lot more chicken, by volume, than ground yellow corn for it to remain first if all the ingredients were measured with the same amounts of their natural water.
It’s like comparing dried apples to whole apples to applesauce. So 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 diet than corn. Not unless you show me your whole recipe. And, unfortunately for the consumer, labeling laws protect the manufacturer's secrecy here.
So how does that relate to fillers?
Well... in this case, the corn meal and corn gluten might well be what we'd traditionally consider the fillers. Here's my reasoning:
While the gluten might be a highly digestible protein source, in the context of a bag covered with glorious pictures of veggies and meats... it's not exactly what I’m being led to believe I'm paying for. The corn subs in for those more desirable ingredients. Hence, according to our working definition, it's a filler.
Not that there’s anything wrong with corn… but I’d rather feed my pet a wider variety of highly digestible, more biologically appropriate ingredients... and you’ve just suckered me into thinking I’m buying all those gorgeous meats and veggies pictured on the front of the bag.
#3 Consider the way whole ingredients are represented
Pet food manufacturers know you look at the first few ingredients, so apart from confusing you with the moisture content, they're effectively able to insert fillers by gaming the system. 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. So while something that says "fish" is listed first and third, water is effectively the first ingredient. And while corn products are listed second and fourth, when added together they comprise the bulk of this diet.
Not only is the pet food company playing apples and applesauce with naturally hydrated and dehydrated ingredients, it’s splitting the fish into two parts 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.
So 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, that this product smells and tastes well enough of fish to make our carnivorous cats happy, and ostensibly contains enough protein to meet their metabolic needs.
But here's the question: Are these corn-based "filler"-rich diets better than their fishier, more chicken-y avatars? Or is the fact that they're offering a correct nutrient balance good enough?
That's the zillion-dollar question. Because if it is good enough, then the question of fillers is effectively resolved and we can content ourselves with feeding grain-based diets with impunity -- regardless of what our carnivores might prefer to eat in the wild. In which case, the word "filler" can exit our nutritional lexicon forever and we can replace all those pretty pictures of meats that grace our pet food packaging with amber waves of grain.