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Animal nutrition

A diet of chicken and corn

Studies find that the majority of dog food in Brazil is based on a less-than-ideal formula of these two ingredients

On average, 60% of the nutrients in the dog foods studied were from animal sources and 40% from vegetables

Léo Ramos Chaves

Dog and cat food packaging usually includes a picture of what is supposedly the product’s main ingredient. But none of them feature pictures of corn or poultry by-products such as offal meal, despite the fact that these are the two ingredients most eaten by Brazilian pets, according to two studies conducted at the University of São Paulo (USP). Agronomist Luiz Antônio Martinelli, from the Center for Nuclear Energy in Agriculture (CENA) at USP’s Piracicaba campus, says that beef or fish, considered high-quality food sources for cats, are almost entirely absent from industrialized food for these animals.

One of the studies analyzed 82 samples of 25 brands of dog food, both dry and wet, and found that on average, 60% of the nutritional content was of animal origin and 40% from vegetables. “The packaging gives the customer the impression the product contains high-quality ingredients, but actually, almost everything is reduced to corn and chicken,” says Martinelli. “This isn’t illegal, because Brazilian legislation on the matter is highly permissive.” The results of the study were published in the journal PeerJ on February 20 this year.

The conclusions of the second study, which examined the composition of 52 samples of 28 brands of cat food, were similar. Although the percentage of animal protein—essentially chicken—detected in cat food was higher on average than in processed dog food, the level of vegetable ingredients, again corn, as well as occasionally soybean, was still considered excessive by the researchers. Only 20% of the samples had vegetable contents lower than 10%, with most high in carbohydrates. “Dogs are flexible carnivores that through evolution have adapted to a diet that includes more vegetables,” says biologist Janaina Leite, a master’s student at CENA who analyzed the cat food. “But the cat is a more restricted carnivore, less able to digest carbohydrates. Some authors therefore recommend that carbohydrates should represent at most 10% of their diet.”

The packaging may show a steak while the food actually only contains beef flavoring, says Luiz Antônio Martinelli, from CENA-USP

Even in samples of wet cat food whose labels emphasized that they contained beef or fish, the level of animal ingredients never exceeded 25%, according to CENA’s analysis. The fear is that in the long term, the excessive carbohydrate from corn can lead to a higher incidence of diabetes and kidney problems in cats, a fact that has been supported by numerous studies. A paper containing detailed results of the cat food study has been submitted to a scientific journal and is awaiting approval.

To determine which ingredients are present in the food and in what quantity, Martinelli and his group identify the proportion of two stable carbon variants (isotopes) and two of nitrogen. Every plant group and animal protein type has a distinct isotopic signature. By analyzing the proportions of two carbon isotopes—the heavy and rare carbon 13 and the light and abundant carbon 12—it is possible to determine whether the food contains plants from group C3 (soybean, rice, and wheat) or C4 (corn). Vegetables are classified as C3 or C4 depending on their photosynthesis process. A combination of carbon dioxide and sunlight causes chemical reactions in plants that generate sugar molecules with either three or four carbon atoms (defined as C3 or C4, respectively).

A similar method can be used to determine which types of meat the food contains (beef, pork, chicken, or fish), but based on two different forms of nitrogen: the rarer nitrogen 15 and the more common nitrogen 14. “Isotope analysis is a recognized method of studying the composition of food and beverages, as well as the dietary profile of populations,” says Martinelli, who has already used this approach to study wines, beers, and soy sauce.

Léo Ramos Chaves According to the study, most cat food samples contained excessive levels of carbohydrate from cornLéo Ramos Chaves

Because owners care so much for their pets, they place a greater value on products with ingredients they consider high quality. According to Martinelli’s group, even the premium, more expensive, and supposedly better quality pet foods that are associated with beef or fish ingredients are usually composed primarily of chicken and corn, which are cheaper in Brazil. “Current legislation suggests that ingredients should be listed on the label in descending order, from the most abundant to the least, but this is only a recommendation,” says Leonardo Galera, a PhD student at CENA and lead author of the dog food article. The lack of a mandatory legal directive on the issue allows companies to get away with misleading advertising, say the authors of the paper. “Pet food products can show a picture of a steak on the packaging even if they only contain meat flavoring and no real meat,” comments Galera. There is no consensus on the ideal amount of carbohydrate that cats can and should eat.

According to the Brazilian Pet Industry Association (ABINPET), all of its affiliated brands strictly follow Brazilian legislation and comply with standards agreed by the veterinary community. The combination of inputs used in Brazilian pet food follows the guidelines established by international studies, says the leader of the organization. “It is true that chicken is the most common animal protein and corn is the most used vegetable,” ABINPET president José Edson Galvão de França said in a statement. “Industrialized food for dogs and cats should contain between 30% and 60% animal ingredients and 40% to 57% vegetables. The remaining 3–10% should be composed of minerals, vitamins, or additives.”

Qualitative ingredients
The current labeling rules for pet food in Brazil are established through Ministry of Agriculture Regulation 30, which came into force on August 5, 2009. The document, which has been amended several times, requires only that manufacturers specify basic “qualitative” information about the ingredients of a product, with no need to mention quantities. “Regarding labeling, manufacturers are obligated to clearly inform consumers of what ingredients are contained in each product,” says França. “Regarding packaging and marketing, as long as they follow the law and good practices, manufacturers are allowed to draw attention to the unique aspects of their product and to decide how to communicate them to the consumer.” Article 43 of the regulation states that photos and descriptions on product packaging should not “be misleading, wrong, confusing, or deceiving, even by omission,” with respect to composition and quality.

The Brazilian pet food market is worth about R$20 billion per year

The CENA researchers did not disclose the names of the brands they analyzed. The initial objective of the study was to obtain an overview of the products on the market in Brazil, a country with about 130 million pets, including dogs, cats, fish, and birds. However, they are now collecting a wider sample of the products available in the sector, which is worth more than R$20 billion per year, in order to conduct individual brand analyses in the future. They also plan to test how easily different pet foods are digested. “It is no good a pet food containing a certain ingredient of animal origin if this ingredient is difficult to digest,” says agronomist Adibe Luiz Abdalla Filho, another author of the study, who is studying a PhD at CENA.

Scientific article
GALERA, L. A. et al. Carbon and nitrogen isotopic composition of commercial dog food in Brazil. PeerJ. Feb. 22, 2019.