Commercial Raw Pet Food Phosphorus Discrepancy Exposed

The Hidden Ingredient in Commercial Raw Pet Food

A new study from Ludwig-Maximilians-Universität München has revealed a significant difference between the raw and canned forms of the same pet food. Researchers found that a key indicator of added inorganic phosphorus disappears after the canning process, potentially masking how much of this supplement manufacturers use.

Canning Masks Inorganic Phosphorus Levels

Led by Susanne Löffelmann and Birgit Dobenecker, the German nutrition team tested 18 variations of a wet cat food formula. They added four common inorganic phosphorus sources—phosphoric acid (H₃PO₄), monosodium phosphate (NaH₂PO₄·H₂O), monopotassium phosphate (KH₂PO₄), and dicalcium phosphate (CaHPO₄)—at different levels. For each recipe, researchers prepared a raw version and an identical canned version.

Using a specialized solubility test, they measured phosphorus that dissolves in water within one minute (Psol1). In raw samples, Psol1 levels correlated directly with the amount of inorganic phosphorus added. However, this clear signal vanished after canning. The heat and pressure of processing dramatically reduced Psol1, even though the total phosphorus content remained the same. This finding suggests that by measuring finished products, we likely underestimate how much supplemental inorganic phosphorus is in commercial canned food. Since European regulations do not require declaring these additives, pet owners and veterinarians lack critical information.

Pathogenic Bacteria Are Common in Raw Pet Food

Separate research from the University of Porto provides a stark warning about microbial safety. Between September 2019 and January 2020, investigators analyzed raw meat-based diets (RMBDs) in Portugal. A high percentage of samples were contaminated with zoonotic pathogens, meaning bacteria that can spread from animals to humans.

The study found Salmonella in a significant number of products. More concerning, they identified pathogenic Escherichia coli (E. coli) clones carrying the mcr gene. This gene confers resistance to colistin, an antibiotic of last resort for treating severe human infections. These resistant bacteria can colonize a pet’s digestive tract and be shed into the household environment, creating a potential reservoir for human exposure. This research confirms that RMBDs are not a sterile product and pose a tangible, if often overlooked, public health risk.

Why Phosphorus Additives and Pathogens Matter for Pet Health

The two studies highlight distinct but serious concerns. Excess inorganic phosphorus is not an inert filler. In dogs and cats, high intake is associated with detrimental effects on kidney health and can accelerate the progression of chronic kidney disease (CKD). For pet owners managing a condition like CKD, precise dietary phosphorus control is a cornerstone of care, as discussed in our guide on the best cat food for kidney disease. Not knowing the amount or source of phosphorus in a food undermines this medical management.

The pathogen risk from raw diets has direct and indirect consequences. Pets may experience acute gastrointestinal illness from Salmonella or pathogenic E. coli. Asymptomatic shedding is also common, putting all household members, particularly children, the elderly, or immunocompromised individuals, at risk. This adds a layer of complexity for owners who choose raw diets for perceived benefits, as they must implement rigorous hygienic handling protocols that many may not follow consistently.

Making Informed Choices for Your Pet’s Diet

Choosing a pet food requires weighing these evidence-based risks. For owners considering or currently using a raw meat-based diet, the University of Porto study is a clear call to action. Handle these products like raw meat for human consumption: use separate utensils, clean surfaces thoroughly, and wash hands immediately after handling. Be aware of the zoonotic risk, especially in multi-pet or family households.

For those using commercial wet or dry foods, the phosphorus study reveals a transparency issue. Look for brands that voluntarily provide detailed nutritional information, including phosphorus content and its source. When a pet has a health condition like kidney disease or hyperthyroidism—a condition that also affects organ function, detailed in our article on cat hyperthyroidism and heart disease—a veterinary therapeutic diet formulated with controlled, high-quality phosphorus sources is often the safest choice.

Ultimately, these studies reinforce that diet is a medical decision. A consultation with a veterinarian or a board-certified veterinary nutritionist is the best step to navigate the balance between nutritional adequacy, safety from pathogens, and management of specific health needs.

Sources:
https://pubmed.ncbi.nlm.nih.gov/41456310/
https://pubmed.ncbi.nlm.nih.gov/38699902/
https://pubmed.ncbi.nlm.nih.gov/37003096/