Pet owners are spending more money on their pets than ever—last year they spent $72 billion—and they spend more on pet food than any other category.

Premium dog food logs in as the most frequent type of pet food purchased, and most of that spending goes toward rising prices and sales of higher-priced dog food made with quality ingredients.

In response, some pet food companies are developing diets that more closely resemble human food than what we traditionally think of as dog food: diets that incorporate human-grade meat and vegetable ingredients that pass United States Department of Agriculture (USDA) inspections.

But there hasn’t been a lot of research done on these new dog food diets. A new study from researchers at the University of Illinois (UI) aimed to change that.

According to the study, “For a pet diet to be labeled as human-grade, every ingredient and the finished food must be stored, handled, processed, and transported according to the current good manufacturing practices for human edible foods.”

One of the goals of the study was to help determine feeding guidelines for specialized diets like these. Since the diets are more similar to human foods than traditional kibble, corresponding author Kelly Swanson, PhD, MS, a professor of animal and nutritional sciences at UI, said there are risks in using formulas derived from traditional pet foods.

“Typical pet foods are generally less digestible than human foods—that’s why feeding guidelines are different from the USDA nutrition guidelines for humans,” Swanson said. “But if you apply the traditional dog food guidelines for metabolizing energy to human-grade dog foods, you risk overfeeding because these foods are so nutrient-dense.”

Swanson’s team tested six commercial dog foods made with minimally processed human-grade ingredients such as rice, carrots, broccoli, chicken, and lamb, and supplemented with human-quality vitamins and minerals.

The researchers determined the chemical composition of the six diets as well as their nutrient and amino acid digestibility and energy content. The team then fed the dog food to roosters who had undergone surgery to remove the cecum (an intestinal pouch that contains bacteria that can break down nutrients and might have obscured the results). Roosters who are surgically altered in this way have digestive systems similar to those of cats and dogs, making them a popular model for studying the effects of pet food. Each rooster was randomly assigned one of the six dog food varieties.

Based on their analysis of the roosters’ feces, the researchers determined that all of the diets were highly digestible, and that protein, amino acids, and other nutrients were easily absorbed into the roosters’ bloodstreams.

Although the study included a single product line, Swanson believes the outcomes are likely to translate to similar pet diets using human-grade ingredients. “Individual foods have to be tested but our results should apply to other products if they’re truly using human-grade ingredients. There might be some small differences, but ultimately, they should still be highly digestible,” he said.

Swanson is currently testing the diets, along with similar diets from other companies, with dogs.

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