We hold these truths to be self-evident: that the guaranteed analysis on a pet food label tells us what our pets are getting. Right?

Wrong.

Not all nutrients are created equal, and understanding pet food labels won’t tell you the whole story about what your dog or cat can actually use. Two foods with identical protein percentages can produce completely different results. The secret isn’t in the numbers – it’s in something called bioavailability.

Think of it this way: it’s not just what nutrients are in the food, it’s whether your pet’s body can actually absorb and use them. There’s a real difference between nutrients that look good on paper and nutrients that actually nourish your pet. For an overview of the different types of pet foods available, check out my blog, Pet Food: Kibble, Wet, Homemade or Raw.

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What Is Bioavailability, and Why Should You Care About it in Your Pet Food?

Bioavailability is essentially how much of a nutrient your pet’s body can actually absorb and use after eating it. You could have a food that’s technically loaded with protein, vitamins, and minerals, but if your pet’s digestive system can’t break them down and absorb them effectively, they’re not doing much good.

During my house calls in Holly Springs and throughout Wake County, I often help pet parents decode these quality differences. Two dogs of similar size and age might both eat foods with comparable protein percentages on the label, but one could have a gorgeous, shiny coat and great muscle tone while the other looks dull and struggles with energy. Often, the difference comes down to the quality and bioavailability of those nutrients.

The Protein Puzzle: Not All Proteins Are Equal for Dogs and Cats

Let’s start with protein, since it’s usually the first thing pet parents look at on a food label. The guaranteed analysis might tell you a food contains 26% protein, but that number doesn’t tell you anything about protein quality or digestibility.

Source Matters Enormously

High-quality animal proteins like deboned chicken, fish, or lamb are what we call “complete proteins” – they contain all the essential amino acids your pet needs in the right proportions. These proteins are also highly digestible, meaning your pet’s body can break them down and use them efficiently.

On the other hand, plant proteins like corn gluten meal or wheat gluten can boost that protein percentage on the label, but they’re incomplete proteins and often much harder for dogs and cats to digest. For cats, especially, who are obligate carnivores, plant proteins just don’t provide what their bodies are designed to use.

Meat by-products or meat meals aren’t necessarily bad – a high-quality chicken meal can actually be more concentrated in protein than fresh chicken because the water has been removed. But quality can vary widely depending on which parts of the animal are used and how they’re processed.

Processing Makes a Difference

How a protein is processed dramatically affects its availability to your pet’s body. Gentle cooking methods preserve more of the protein structure, while high-heat processing can damage amino acids and make them less digestible.

This is one reason why some people advocate for raw foods – raw proteins haven’t been damaged by processing. However, there are important safety considerations with raw diets that we discussed in my previous post.

The Vitamin and Mineral Maze

Vitamins and minerals are where things get really interesting from a bioavailability standpoint. You’ll often see long lists of added vitamins and minerals on pet food labels, but the form these nutrients are in makes all the difference.

Natural vs. Synthetic: The Ongoing Debate

Some vitamins and minerals that occur naturally in whole food ingredients are more readily absorbed than their synthetic counterparts. For example, vitamin E from natural sources (listed as mixed tocopherols) is generally more bioavailable than synthetic vitamin E.

However – and this is important – some synthetic vitamins are actually better absorbed than their natural versions. The relationship isn’t straightforward, which is why this topic can be so confusing.

Mineral Forms Matter More Than You Think

Minerals are particularly tricky. The same mineral can be provided in several different forms, and some are much more bioavailable than others.

Chelated minerals, where the mineral is bound to an amino acid or protein, are generally much better absorbed than their inorganic counterparts. For instance, chelated zinc is more bioavailable than zinc oxide. Unfortunately, chelated minerals are more expensive, so not all pet food manufacturers use them.

Iron is another great example. Iron from animal sources (heme iron) is much more easily absorbed than iron from plant sources or added iron supplements. This is yet another reason why animal-based proteins tend to be superior for our carnivorous pets.

The Copper Conundrum: A Cautionary Tale

Copper provides a striking example of how changes in bioavailability can create unintended consequences when guidelines don’t keep pace. In 1997, the Association of American Feed Control Officials (AAFCO) – the organization that sets nutritional standards for pet food in the United States – changed its recommendations for copper supplementation in dog food. The change was based on research showing that copper oxide had extremely low bioavailability, so AAFCO recommended that manufacturers use more bioavailable forms like copper sulfate or copper chelates (such as copper proteinate) instead.

This seemed reasonable – why use a form of copper that dogs can barely absorb? However, ten years later in 2007, AAFCO removed the maximum limit for copper content in dog food. This created a problematic situation: a more bioavailable form of copper was now being used, but without an adjusted upper limit to account for that increased bioavailability.

According to a 2021 article in the Journal of the American Veterinary Medical Association, veterinarians have observed an apparent increase in copper-associated liver disease in dogs over the past 15-20 years, coinciding with these guideline changes. The authors noted that “the onset of this increase appears to have coincided with a change in the type of copper used in premixes added to commercial dog foods.”

This situation illustrates the quagmire that even well-meaning pet parents face: you’re trying to feed a food that meets AAFCO guidelines, but those guidelines may not reflect the latest science on bioavailability. It’s a sobering reminder that “meeting minimum requirements” on a label doesn’t tell the whole story.

Fats: The Good, The Bad, and The Rancid Nutrient

Fats often get overlooked in discussions about pet food, but they’re crucial for your pet’s health and another area where quality varies dramatically.

Omega Fatty Acids: The Balancing Act

You’ve probably heard about omega-3 and omega-6 fatty acids. Both are essential, but the ratio between them matters enormously for your pet’s health. Many commercial pet foods are heavy on omega-6 fatty acids (often from corn or soy oil) but light on omega-3s.

The best omega-3 fatty acids for pets come from fish oil or whole fish. Plant-based omega-3s, like those from flaxseed, have to be converted by your pet’s body into the forms they can actually use, and dogs and cats aren’t very efficient at this conversion.

Freshness Is Critical

Fats can go rancid when exposed to oxygen, light, and heat. Rancid fats are problematic for two important reasons: oxidation damages fat-soluble vitamins and beneficial antioxidants, reducing their nutritional value, and the oxidation products themselves may pose health risks. Research has linked consumption of oxidized fats to various health concerns in animal studies. High-quality manufacturers are careful about preventing rancidity with natural preservatives and proper storage, but not all companies are equally diligent.

If your pet’s food smells off or your pet suddenly starts refusing a food they used to love, rancid fats could be the culprit.

The Carbohydrate Conundrum in Pet Nutrition

Carbohydrates are probably the most controversial macronutrient in pet food, and bioavailability plays a big role in that controversy.

Digestible vs. Indigestible Carbs

Dogs can digest certain carbohydrates reasonably well, though cats have a more limited ability. But not all carbs are created equal. Highly processed carbohydrates, such as corn syrup, are rapidly absorbed and can cause blood sugar spikes. Whole grains and vegetables provide more steady energy and often come with beneficial fiber.

The problem is that many pet foods rely heavily on inexpensive, highly processed carbohydrates as fillers. These provide calories but not much nutritional value, and they can be hard on your pet’s digestive system.

How Processing Affects Everything

One of the biggest factors affecting nutrient bioavailability is how the food is processed. This is where the different food types we discussed in my last post really start to show their differences.

Kibble and High-Heat Processing

Most dry kibble is processed at high heat and pressure, which can damage heat-sensitive vitamins such as vitamin C and some B vitamins. This is why you’ll see these vitamins added back in after processing. The proteins can also be affected, with some amino acids becoming less available.

Gentler Processing Methods Versus Raw Foods

Some newer kibble manufacturing methods use lower temperatures or air-drying to preserve more nutrients. Freeze-dried and dehydrated foods often retain more of their original nutrient content because they use minimal heat.

Fresh and raw foods undergo the least processing, so their nutrients remain in their most bioavailable forms. As I discussed in my previous post about choosing pet food, raw feeding remains highly controversial in veterinary medicine due to safety concerns, but some pets do appear to thrive on these diets. The vast majority of veterinarians don’t recommend raw food diets.

The Problem with Minimums (and Missing Maximums)

Here’s another challenge that makes navigating pet nutrition so difficult: AAFCO sets minimum requirements for most nutrients, but maximum limits exist for only a handful of nutrients where toxicity is well-established. This creates real problems in certain situations.

When One Size Doesn’t Fit All

AAFCO currently recognizes only two life stages for nutritional requirements: “growth and reproduction” and “adult maintenance.” As noted in veterinary nutrition research, neither AAFCO nor the National Research Council (NRC) – the scientific body that provides the research basis for these standards – recognizes that nutritional requirements may change in healthy, older adult dogs and cats. Research shows that the adult life stage should really be divided into young adult, mature adult, and geriatric stages to address the metabolic and physiological changes that occur as animals age.

The Protein Paradox

This limitation becomes especially apparent with protein. AAFCO sets a minimum protein requirement (18% dry matter for adult dogs, 26% for adult cats), but no maximum. For most healthy pets, this isn’t a problem. However, for pets with certain health conditions, particularly kidney disease, this creates a dilemma.

Dogs and cats with chronic kidney disease often need reduced protein diets to help manage their condition. Therapeutic renal diets for dogs typically contain 25-55 grams of protein per 1000 calories – often well below the AAFCO minimum of 45 grams per 1000 calories for adult maintenance. This means that foods specifically formulated to help pets with kidney disease cannot carry an “AAFCO complete and balanced” statement, even though they may be exactly what those pets need.

The flip side is equally problematic: a food can contain very high protein levels and still meet AAFCO standards, which might not be ideal for senior dogs with early kidney changes or certain other health conditions.

This isn’t a criticism of AAFCO – the organization does important work establishing baseline nutritional standards. But it highlights why working with your veterinarian to choose the right food for your individual pet’s needs is so important, especially as your pet ages or develops health conditions.

Understanding Pet Food Labels: What This Means for You

So how do you use this information when choosing food for your pet? Here are some practical tips:

Look Beyond the Guaranteed Analysis

Those minimum percentages on the label don’t tell you much about quality or bioavailability. Look at the ingredient list and research the manufacturer’s quality standards.

Consider the Whole Picture

A food with slightly lower protein numbers but higher-quality protein sources might be better than one with impressive numbers from questionable sources. The form of minerals matters. The freshness of fats matters. The processing methods matter.

Understand That “Complete and Balanced” Has Limitations

An AAFCO statement tells you the food meets minimum nutritional requirements for healthy pets at a particular life stage. It doesn’t tell you about ingredient quality, bioavailability, or whether the food is right for your pet’s individual needs – especially if your pet is a senior or has health issues.

Watch Your Pet

The best measure of whether a food is working is how your pet looks and feels. A shiny coat, good energy levels, healthy weight, and normal bathroom habits are better indicators than any label.

Don’t Be Afraid to Ask Questions

Reputable pet food companies should be able to tell you about their sourcing, processing methods, quality control measures, and why they chose particular forms of vitamins and minerals. If they can’t or won’t provide this information, that tells you something too.

The Bottom Line for the Best Foods for Your Pet

Pet food quality and nutrient bioavailability are one of those topics that can make your head spin, but the core concept is simple: it’s not just what’s in the food, it’s whether your pet can actually use it. High-quality ingredients, appropriate processing methods, and careful attention to nutrient forms all contribute to making a food that truly nourishes your pet.

The regulatory system tries to protect our pets by setting nutritional minimums, but it has limitations. Guidelines can lag behind the science. One-size-fits-all standards don’t account for individual variation or special needs. And even well-intentioned changes – like switching to more bioavailable forms of nutrients – can have unintended consequences if maximum limits aren’t adjusted accordingly.

Remember, the most expensive food isn’t necessarily the best, but the cheapest food is rarely optimal. Look for companies that prioritize quality ingredients, are transparent about their sourcing and manufacturing processes, and can explain the “why” behind their formulation choices.

Every pet is different, and what works beautifully for one might not be ideal for another. That’s why I always encourage pet parents to work with their veterinarian to find the best nutrition plan for their individual furry family member – taking into account not just what the label says, but your pet’s age, health status, and how they’re actually doing on the food.

Good nutrition is one of the most important gifts you can give your pet, and understanding how nutrients actually work in their bodies helps you make choices that will keep them healthy and happy for years to come.

Dr. Shanda Streeter provides comprehensive veterinary care through convenient house calls in Holly Springs, Apex, Fuquay-Varina, and throughout Wake County and the Research Triangle area, including nutritional consultations to help pet parents make the best feeding decisions for their individual pets..