Because many seemingly normal pets have kidney disease, we recommended all adult pets avoid excess dietary phosphorus. This can be accomplished by meeting the minimum recommended dietary allowance for phosphorus. The National Research Council employs the same logic for human nutritional guidelines. Check the level of phosphorus in your pet's food. The minimum dietary allowance is 0.55% (dry matter basis). Some pet foods contain up to three times this amount.

More information about Kidney Disease
The kidneys are two of the most important organs in the body. They remove protein and mineral excess and toxic substances, reabsorb needed nutrients, recycle water, and control the balance of acids or bases in the body. When kidney disease affects animals, they eventually lose the ability to remove waste products and excess nutrients from the blood, which can ultimately lead to death.

Research shows that excess dietary phosphorus can accelerate the progression of kidney disease. Many pet owners are unaware of the high incidence of kidney disease in dogs and cats. Studies by the Morris Animal Foundation in 1986 and 1991 concluded that kidney disease was the leading cause of non-accidental death in cats and the second leading cause of non-accidental death in dogs. Another researcher found kidney disease was second only to cancer as the leading cause of death in dogs. A third study concluded that 20% of dogs over five years old have more than a 75% reduction in kidney function.²

Once started, kidney disease is unstoppable. As the disease progress (months to years), kidney function continues to decline. Health reaches a critical level when the kidneys fail. Kidney disease is not easy to detect, especially in its early stages. Routine tests used by veterinarians to identify kidney disease (serum creatinine and serum urea nitrogen) cannot do so until about three-fourths of kidney function is lost. ¹

What is the link between kidney disease and excess phosphorus in pet foods?
Causes of kidney disease are difficult to avoid. Causes include aging, bacterial infections, hypertension, toxins (e.g., antifreeze and certain drugs), or it can be an inherited trait from the parents. Thus, prevention of kidney disease is difficult, but the progression of kidney disease can be slowed.

Research in dogs and cats with advanced kidney disease revealed that decreasing the level of phosphorus in the food slowed the progression and reduced the severity of kidney disease, thereby improving the length of survival. ^4,5 In the study using dogs, two identical foods were fed except for the level of phosphorus. The high level of phosphorus was 1.50% and the low level was 0.44% of the food's dry matter. After two years of feeding these foods, only 33% of the dogs fed the high phosphorus food were alive, but more than 75% of the dogs fed the low phosphorus food were alive. In the study using cats, the food's dry matter phosphorus levels were similar to those used in the dog study (0.42% and 1.56%). The kidneys of the cats fed the low phosphorus food had little or no changes. The kidneys of the cats fed the high phosphorus food had deteriorated when examined under the microscope.

Because low phosphorus foods slowed the deterioration of kidney function in dogs and cats with advanced kidney disease, it is logical that limiting excesses of phosphorus throughout an animal's adult life can reduce the progression of kidney disease in its earlier stages when diagnosis is so difficult.

The health care profession applies the same reasoning to our foods for limiting the intake of cholesterol, fat, and sodium. Since we cannot predict accurately who among us will get coronary disease or high blood pressure, the experts recommend that all adults eat less cholesterol, fat, and sodium as part of a sensible nutritional plan.

Sometimes what's not in the bag is what counts.
How can pet owners pick a pet food that contains lesser amounts of phosphorus? Either ask your veterinarian or call the pet food manufacturer's customer service department for information about the level of phosphorus in their foods.

Formulating a pet food, with adequate but not excessive levels of phosphorus, requires medical knowledge, nutritional expertise, and careful selection of ingredients. Ingredients such as meat and bone meal and fish meal can contain high levels of bone that adds excess of phosphorus. Because pet food manufacturers are not required to list phosphorus on the nutritional label guarantees, products containing fish meal and other meat and bone meals should be evaluated with added attention.

The minimum dietary allowance for phosphorus in adult dogs and cats is 0.5% (dry matter basis).⁶ There are products sold in both specialty stores and grocery stores that contain 1% to 11/2% phosphorus--two to three times the minimal necessary amount.To do the best for our pets we should select foods that contain lesser amounts of certain nutrients. In the case of phosphorus, more of this nutrient is not better for your pet and could be influencing the progression of undiagnosed kidney disease.

1. Bronson, R., American Journal of Veterinary Research, 1982, 43:22057-2059.
2. Leibesteder, J. & coworkers, WSAVA World Congress Proceedings, 1991, p. 271-274.
3. Osborne, C. And Stevens, B., Handbook of Canine & Feline Urinalysis, 1981, p47.
4. Brown, S. & coworkers, Journal of the American Society of Nephrology, 1991, 1:1169-1179.
5. Ross, L. & coworkers, American Journal of Veterinary Research, 192, 43: 1023-1026.
6. 1995 Association of American Feed Control Officials, Official Publication, p.134-135.

The Authors.

Kathy L. Gross, Ph.D., P.A.S. Dr. Gross joined Hill's Pet Nutrition, Inc. in 1990 after serving as postdoctoral research associate at the US Department of Agriculture Research Service Human Nutrition Research Center on Aging at Tufts University. Dr. Gross' expertise is in gastrointestinal tract nutrient metabolism, amino acid metabolism, and interactions of nutrition and immunology. She has authored or co-authored 41 research publications and is adjunct professor at Kansas State University.

Timothy A. Allen, D.V.M., Diplomate A.C.V.I.M. Dr. Allen completed and in internship and medical residency at the Animal Medical Center in New York City after receiving his D.V.M. in 1972. He then served two years as Research Associate in the Laboratory of Medical Biochemistry at the Rockefeller University, New York City. Dr. Allen was in private veterinary practice for four years and then a faculty member at Colorado State University for eight years before joining Hill's Pet Nutrition, Inc. in 1988. Dr. Allen is board certified in Veterinary Internal Medicine. He is an expert in nephrology and urology. He has authored or co-authored over 90 research publications. Dr. Allen is an affiliate faculty member at Colorado State University and an adjunct professor at Kansas State University.

"Reprinted with permission of Hills Science Diet"