Why Fillers and By-Products Harm Your Cat's Nutrition

Pick up the nearest bag of cat food and read the ingredient list. Somewhere in the first five ingredients, you will likely find corn, wheat, soy, rice, or "poultry by-product meal." These are fillers — ingredients that add bulk and calories to cat food at a fraction of the cost of real meat.

They keep manufacturing costs low and profit margins high. They do very little for your cat.

What Counts as a Filler?

A filler is any ingredient included primarily for volume, binding, or cost reduction rather than nutritional value. In cat food, the most common fillers include:

Corn and corn gluten meal: Used as a cheap protein source and binding agent. Cats lack the digestive enzymes to efficiently process corn protein, and it offers a poor amino acid profile compared to animal protein.

Wheat and wheat gluten: Another cheap binder with limited nutritional value for cats. Some cats develop sensitivities to wheat gluten that manifest as skin irritation, digestive upset, or chronic vomiting.

Soy: Contains phytoestrogens that can interfere with thyroid function in cats. Also a common allergen and poorly digestible for obligate carnivores.

Rice and potatoes: Better tolerated than corn or wheat, but still unnecessary carbohydrate sources that contribute to weight gain and blood sugar fluctuations.

Cellulose: Literally powdered wood pulp. Listed as a fiber source, it has zero nutritional value and is included purely to add bulk.

The By-Product Problem

"By-product meal" is one of the most ambiguous terms in pet food. It can include organs (which are actually nutritious), but it can also include feet, beaks, undeveloped eggs, and other parts that vary wildly in nutritional quality from batch to batch.

The issue is not that by-products are inherently bad — organ meats like liver are excellent nutrition. The issue is that "by-product meal" is a catch-all category with no consistency. You have no idea what your cat is actually getting from one bag to the next.

Named, whole-animal ingredients — like "chicken," "beef liver," or "chicken heart" — tell you exactly what is in the food. There is no ambiguity and no batch-to-batch variation.

Why This Matters for Your Cat's Body

Digestive strain: Cats lack the enzyme amylase in their saliva (which breaks down starches) and have limited pancreatic amylase compared to omnivores. Feeding them starch-heavy food forces their pancreas to work harder than it was designed to, which over time can contribute to pancreatic inflammation.

Weight gain: Carbohydrate fillers are efficiently converted to fat storage in cats because their bodies have no metabolic pathway to use carbs as a primary energy source. This is why so many kibble-fed cats are overweight despite eating "recommended" portions.

Allergies and sensitivities: Corn, soy, and wheat are among the most common allergens in cats. Symptoms include chronic scratching, ear infections, digestive upset, and skin lesions. Many cats labeled as "allergic" are simply reacting to fillers they were never meant to eat.

Nutrient dilution: Every gram of filler in cat food is a gram of real meat that is not there. A food with 30% corn has 30% less room for the animal protein your cat actually needs. The guaranteed analysis might look similar on paper, but the quality and bioavailability of nutrients is dramatically different.

How to Read Labels

Ingredients are listed by weight before processing. This means chicken listed first might actually contribute less protein than corn gluten meal listed third, because fresh chicken is 70% water (heavy) while corn gluten meal is dry (lighter but denser in the final product).

Look for foods where the first 3-5 ingredients are all named animal proteins. Avoid anything with corn, wheat, or soy in the top 10. And be wary of "ingredient splitting" — listing corn in multiple forms (corn, corn gluten meal, ground corn) to keep each one lower on the list while the total corn content may be substantial.

The simplest approach? Choose food where you can recognize every ingredient. Clawz recipes use USDA-certified beef and chicken, chicken liver, green beans, and essential vitamins. That is it. No fillers, no by-products, no ingredients you need a chemistry degree to pronounce.

Give Your Cat the Food They Deserve

If you have been thinking about switching to real food, there has never been a better time. Clawz offers a 10-day trial box for just $24.99 — that is $1.25 per meal. Every pouch is gently cooked from USDA-certified meat, vet-formulated for complete nutrition, and delivered frozen to your door.

Not sure where to start? Take the 2-minute quiz and we will build a personalized plan based on your cat's age, weight, and health goals. Free litter is included with every subscription, and you can cancel anytime in 30 seconds.