Cats vs. Dogs: Who Is More Exposed to Heavy Metals in Pet Food?

If you share your home with a cat and a dog, you may have wondered whether one of them is taking in more heavy metals from their food than the other. It's a fair question, and a handful of studies have tested cat and dog foods side by side. Their answers don't all point the same way.

The short answer

It depends on the metal. In a 2021 study from Brazil, lead was above the maximum tolerable level in more of the dog foods than the cat foods, and a 2025 study from South Africa found dog brands over tolerable limits more often than cat brands. Yet the same Brazil study found higher mercury in dry cat foods than in dry dog foods, the Spain study found arsenic and mercury had the highest hazard estimates, especially for cat food, and the China study found a higher arsenic estimate for cats than for dogs. Two of these studies point to one thing: smaller bodies take in more per pound. No study we read crowns one species as more exposed overall.

Why "per pound" matters more than "per bowl"

A bowl of food doesn't tell you much on its own. What researchers look at is how much of a metal an animal takes in compared with its body weight.

The Brazil study did exactly that. Its authors estimated daily intake per kilogram of body weight for dogs of several sizes and for cats across a typical weight range. In that model, smaller animals took in more of each metal per kilogram than larger ones, because they eat more food relative to their size.

The 2025 China study reached a similar point by a different route. It measured lead, cadmium, chromium, mercury, and arsenic in cat and dog foods, then estimated risk for each species. Its authors observed that lighter cats and dogs had higher hazard estimates because of their smaller body mass.

In plain terms, a small dog and a cat may take in more per pound than a large dog eating the same food. That's about size, not species.

Fish-heavy diets and cats

In the Spain study, only two of the dog foods tested were fish-based, so the researchers could compare fish and meat recipes only within cat food. In that comparison, fish-based cat foods had higher arsenic, cadmium, and mercury.

Dog food studies point the same way when fish is the main protein. A 2018 US study of dry dog foods found that fish-based recipes were higher in arsenic, cadmium, and mercury than poultry or red meat recipes.

A UK study by Davies and colleagues, which tested both cat and dog foods, explains why fish matters for arsenic: it can build up in fish and in the animals that eat them, and the authors name the domestic cat as an example.

The Spain authors found that arsenic and mercury had the highest hazard estimates in their study, especially for cat food. For more on mercury and arsenic, including why the form of each matters, see our post on lead, arsenic, and mercury in cat food.

Protein needs and mercury in dry cat food

The Brazil study found more mercury in dry cat foods than in dry dog foods. Its authors offered a possible explanation: cat foods include more protein to meet cats' higher protein needs, and in their samples, animal protein ingredients such as beef meal and chicken by-products had the highest mercury.

The UK study supports the protein part of that picture. Cat diets in that study had more crude protein than dog diets, in line with cats being obligate carnivores.

Treat this as the authors' suggestion, not a settled fact. The Brazil authors did not report which form of mercury was present, and suggested it may not be the methylmercury found in fish. This is one study of foods sold in one country, describing groups of products, not any single bag.

Where dog food came out higher

Dog food came out higher in several comparisons. In the South Africa study, which tested 31 brands, dog brands went over maximum tolerable limits more than cat brands, and recipes built on red meat had the highest total metal levels.

In the Brazil study, dry dog foods had higher aluminum, barium, cobalt, and uranium than dry cat foods, and lead was over the tolerable level in a larger share of dog foods.

Some of what drives these results is specific to dogs, such as red meat recipes and raw food made with game. Our post on heavy metals in dog food covers those factors.

What the research can't tell us yet

These studies are useful, but they have limits worth knowing.

Samples are small and mostly outside the US. The studies tested foods sold in Brazil, China, Spain, South Africa, and the UK. Products and ingredients vary from country to country.

Limits differ by country. The China study judged foods against China's pet feed limits, while others used US or European reference values. In the US, the FDA has no set limits for heavy metals in animal food and acts case by case. Its own sampling found most animal food results below maximum tolerable levels.

These are estimates, not measurements in pets. The hazard figures come from models built on food levels and assumed intake. They don't measure metals in the cats and dogs eating the food.

Long-term effects are open questions. The UK authors say it remains to be seen whether high, long-term arsenic intake affects cats' kidneys.

What to ask for both pets

The same questions work for both pets, and our 5-minute heavy metals check walks you through them. If a company shares results, here's how to read a heavy metal COA. Ask your vet about each pet's diet, since a cat and a dog have different needs. For the people in your home, see our guide to heavy metals in food.

FAQ

Is cat food or dog food higher in heavy metals? It depends on the metal and the study. Dog foods went over tolerable limits more often in the Brazil and South Africa studies, while cat foods ran higher for mercury in the Brazil study. In the Spain study, arsenic and mercury had the highest hazard estimates, especially for cat food, and the China study found a higher arsenic estimate for cats than for dogs.

Why might small pets take in more heavy metals? Smaller animals eat more food for their size, so in exposure models they take in more of each metal per pound of body weight. The Brazil and China studies both found this.

Are fish-based pet foods higher in mercury? In the Spain study, fish-based cat foods had higher mercury, arsenic, and cadmium. In the 2018 US study, fish-based dog foods did too.

Can my cat and dog share the same food? That's a question for your vet. Cats and dogs have different nutritional needs, and AAFCO label statements name the species a food is formulated for.

This article is general information, not veterinary advice. If you have questions about your cat's or dog's health, contact your veterinarian.

Want to know whether a brand tests its cat and dog foods for heavy metals? Heavy Metal Tested is a certification program that helps brands share independent results with owners. Learn how Heavy Metal Tested certification works.