Byproducts and Fillers in Pet Food: Why Vets Say They're Fine

Ask most pet owners about byproducts in pet food and you'll hear "that's gross" or "I'd never feed my dog that." But ask a veterinarian, and you'll get a very different answer: byproducts are actually great for dogs and cats.

This guide tackles two of the biggest myths in pet nutrition — that byproducts are bad and that fillers are useless — and explains what veterinarians actually think about these ingredients.

The Byproduct Myth

What Byproducts Actually Are

Byproducts in pet food are the non-muscle-meat parts of an animal. According to AAFCO, pet food byproducts include:

• Liver — Rich in vitamin A, B vitamins, iron, and copper
• Kidney — High in B12, riboflavin, and iron
• Heart — Excellent source of taurine (essential for cats), CoQ10, and B vitamins
• Lungs — High in protein, low in fat
• Spleen — Rich in iron and protein

What Byproducts Are NOT

A common misconception is that byproducts include hooves, hair, and floor sweepings. This is false. AAFCO explicitly excludes:

• Hooves and horns
• Hair and hide
• Teeth
• Intestinal contents

Organ Meats Are Premium Nutrition

In many human food cultures around the world, organ meats are considered delicacies. They're nutrient-dense, often more so than muscle meat:

The "Filler" Myth

Every Ingredient Costs Money

Think about it from a business perspective: why would a pet food company pay to add an ingredient that serves no purpose? Every ingredient in the formula adds cost — for sourcing, processing, storage, and transportation. If an ingredient is in the food, it's doing something.

Common "Fillers" and What They Actually Do

A Warning About Grain-Free Diets

The "fillers are bad" myth has driven many pet owners toward grain-free diets. But this trend has raised serious health concerns:

Unless your veterinarian has diagnosed your dog with a specific grain allergy (which is rare — most food allergies in dogs are to proteins like beef or chicken, not grains), there is no nutritional reason to avoid grains.

What Should You Actually Look For?

Instead of avoiding byproducts and "fillers," veterinarians recommend focusing on:

1. AAFCO compliance — Does the food meet nutritional standards?
2. Feeding trials — Has the food been actually tested?
3. Company reputation — Does the brand employ veterinary nutritionists?
4. Your pet's individual needs — Age, breed, size, and health conditions matter more than ingredient trends.

The Bottom Line

Byproducts are nutritious organ meats that veterinarians endorse. "Fillers" are functional ingredients with real nutritional purposes. The marketing that demonizes these ingredients is designed to sell more expensive food — not to improve your pet's health.

Use ToxiPets to scan any pet food and get a vet-reviewed breakdown of every ingredient, so you can see past the marketing and understand what's actually in your pet's bowl.