Reading a pet food label is easy. Translating it into usable information is quite another. In case you never tried it, let me offer you this frank observation: Even as a veterinarian, interpreting what’s what on the back of the bag isn’t always easy.

And nowhere is this tougher than when it comes to spotting "real" ingredients versus the so-called "fillers." Mostly, that’s because "fillers" mean different things to different people. And that's where the confusion begins...

Ask most people and they’ll say that fillers are cheap ingredients that serve to "fill pets up." But for many of us, a better definition of a filler might be anything that:

a) Isn’t a biologically appropriate ingredient for the species

b) Adds bulk in lieu of other, more nutritious, or higher quality options

c) Adds nutrients in lieu of other, higher quality options

d) Offers the pet food company a higher profit margin at the expense of quality (especially, when that quality makes a difference to pet health)

Granted, any of the above can be said to march in time to the beholder’s POV. To wit, what’s "biologically appropriate" for any given species (including humans) is as hotly debated as climate change. Though there are some obvious examples of biological impropriety (cats should not be eating corn-based foods, nor should dogs be eating any amount of high-fructose corn syrup), it’s not always so cut and dry.

Which is why many veterinary nutritionists will agree that so-called fillers exist in pet foods, but some will hold they're necessary for maintaining an appropriate nutrient balance. Here’s Angell Memorial’s veterinary nutritionist, Dr. Rebecca Remillard’s approach (speaking of dogs only):

In a sense, [a carbohydrate filler is a much needed] part of the diet. The point to consider when thinking about why carbohydrates constitute a large fraction of most pet foods [is that] on a dry matter basis (no water included), the total of all five nutrients must equal 100. So the sum of protein plus fat plus carbohydrate (starch plus fiber) plus minerals plus vitamins must equal 100. There are no other components to consider.

If all the dog's nutrient requirements ... can be met in a twenty percent protein, ten percent fat, ten percent for all vitamins and minerals, what has to comprise the remaining sixty percent?

The least harmful is carbohydrate in some various form. There are no other nutrients. If you wish to feed less carbohydrate then you'll have to overfeed some other nutrient like protein or fat.

I wholeheartedly agree, and I absolutely respect Dr. Remillard. Nonetheless, my problem with her take (and I would love it if she would offer her opinion here) is three-fold: 

1) I’m OK with feeding dogs more protein than twenty percent, as long as they have no aggression issues. Science hasn’t yet dictated this magic number’s preeminence.

2) This excerpt would seem to suggest that all carbs are created equal. But they’re not. This we know.

3) Fillers shouldn’t always be defined as carbs. To my nit-picky, curmudgeonly way of thinking, a filler is any substitute for something better that could have been offered in its stead. (Though I’ll freely agree that “better” isn’t exactly easy to agree upon, and fillers almost always arrive in the guise of carbs.)

(All of which makes me think Dr. Remillard and I simply have a differing opinion on how a filler is defined.)

Ultimately though, it’s the issue of food price and profit margin that raises the trickiest issue. How far should pet food companies go to offer a nutritionally balanced diet? When are substitutions for high-quality meats, vegetables, and grains considered acceptable? Do these substitutions (i.e., fillers) really make a difference to pet health? Should health ever be sacrificed for profit?

Unfortunately, the answer to this last question is a resounding "yes" in our culture. Otherwise, why would places like McDonald’s and "foods" like Coca-Cola exist? But I digress … which means it’s time to step away from the keyboard and take a break. Stay tuned for part 2 later this week: how best to spot fillers in pet foods.

Dr. Patty Khuly

Art of the day: "Yummy" by Melissa Gray