Most people pet owners trust that packaged dog food is safe. A recent investigation now shows that some popular products may contain harmful substances.
The Clean Label Project, a Colorado-based non-profit organization, tested 79 samples of best-selling dog foods.
The team checks consumer-products for purity and gives certified-labels to brands that meet strict-standards. A federally-certified laboratory carried out 11,376 individual-tests.
The lab looked for heavy metals like lead, arsenic, mercury, and cadmium. It also tested for pesticides, plastics, and a chemical called acrylamide.
“The levels of heavy metals and other contaminants we found were alarming,” said Molly Hamilton, the executive-director of Clean Label Project.
The report showed that dog foods contained three-to-13-times more heavy metals than human foods tested by the group over the past decade.
Dr. Joseph Wakshlag, a professor and nutritional-specialist at Cornell University College of Veterinary Medicine in Ithaca, New York, conducted similar research in 2018.
“We wrote a paper in 2018 comparing the intake of heavy metals between people and dogs based on a calorie,” Wakshlag said. “Compared to a person, we found dogs consumed three to seven times the amounts of heavy metals each day.”
Wakshlag did not take part in the new investigation, but the findings match earlier results.
Heavy metals can accumulate in a dog’s kidneys and liver over time, potentially contributing to chronic disease.
Exposure to metals such as lead and cadmium has also been linked to an increased risk of cancer in dogs.
According to the American Veterinary Medical Association, about one in four dogs will develop cancer during life.
A 2021 study found that 81 percent of tested dog foods exceeded the maximum-tolerated level for mercury. All products in that study exceeded the limit for lead.
The US Environmental Protection Agency states that no safe level of lead exists for humans. The agency does not list safe levels for dogs.
Are there clear safety standards?
Safety standards for animal feed come from the Association of American Feed Control Officials and the National Research Council. These guidelines apply to many types of animals.
“The difficulty of using NRC or AAFCO expectations is that they don’t have guidelines that are specific to dogs. Pet food is lumped into the same category as agricultural animals,” Hamilton said.
“The prevailing industry theory is that dogs have a higher tolerance for heavy metals than humans, though what this theory is based on is up for debate.”
Scientists still lack long-term-studies that follow dogs for many years on different diets.
“How would chronic consumption of these contaminants at really high levels affect a dog? We don’t know,” Wakshlag said. “We have very few studies that have followed dogs for years on different diets to find those answers.”
Dry food contamination
The study found that dry dog food, also known as kibble, contained the highest levels of contaminants.
Air-dried and freeze-dried foods followed next. Fresh and frozen foods had the lowest levels.
Lead and mercury levels in dry food were about 21-times higher than in fresh and frozen foods. Kibble also had over 13-times more arsenic and six-times more cadmium.
More than 85-percent of dog owners feed dry-food daily. Many dogs eat the same product for years.
“If dry dog food is all they consume, it’s possible the accumulation of heavy metals could be contributing to the higher cancer rate in dogs,” Hamilton said.
Fresh and frozen foods
Fresh and frozen dog foods entered the mainstream market in 2006. These products contain at least 70-percent water.
Water usually contains fewer heavy metals than a condensed-piece of kibble. However, dogs must eat more fresh or frozen food to get the same calories.
“You also can’t take those numbers at face value, because a dog has to eat about 3 cups of fresh or frozen dog food to get the same calories and nutrients as 1 cup of dry food,” Wakshlag said.
“Therefore, the dog’s exposure to heavy metals in fresh or frozen foods goes up because it has to eat two to three times as much.”
Chemicals found in dog food
The investigation also found high levels of acrylamide in dry dog food. One product tested at 780-parts-per-billion.
“I’ve never seen acrylamide at a 780 level in a food,” Wakshlag said. “That company must be cooking the hell out of their food or using ingredients that are leading to more acrylamide formation.”
“That’s like a person eating five servings of french fries every day in terms of acrylamide exposure.”
Acrylamide forms when carbohydrate-rich foods cook at high-temperatures above 248-degrees-Fahrenheit.
Scientists consider it likely to cause cancer in humans. Animal-studies show that acrylamide can cause several types of cancer and reduce fertility.
The researchers also tested for plastic-related chemicals. These included Bisphenol-A, Bisphenol-S, and a phthalate called Di(2-ethylhexyl)phthalate.
Dry food again showed the highest levels. Studies in humans link these chemicals to heart disease, diabetes, reproductive problems, and early death. Scientists have not yet studied long-term effects in dogs.
What pet owners can do
“Pet owners care for their dogs as deeply as parents care for their children,” Hamilton said. “They should be able to buy dog food without worrying it might harm their pet.”
The Pet Food Institute, which represents pet-food manufacturers, said it will review the report and continues to monitor safety.
Hamilton advises calm and careful action. A veterinarian can help guide food-choices. If budget allows, fresh or frozen options may reduce exposure.
“If you’re going to keep using dry food, rotate it with other brands to diversify your dog’s diet,” Hamilton said.
“You wouldn’t want to eat the same thing every day for every meal, and many dogs are thrilled to eat new foods. Rotating the diet is probably the best thing you can do.”
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