AAFCO to Set Phosphorus Limit for Cat Foods

Lisa Selvaggio
by Lisa Selvaggio

Cats diagnosed with chronic kidney disease (CKD) may benefit from eating foods that contain less phosphorus, and lower phosphorus levels might also support the kidneys of healthy cats. Unfortunately, it can be difficult to find foods that aren’t high in this mineral. Thanks to research from experts like Dr. Jonathan Stockman, however, more foods with appropriate phosphorus amounts may become available after AAFCO implements a change to the limit for phosphorus in cat foods.

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Dr. Stockman started a 9-month study to look into the link between dietary phosphorus (in this case, 4.8 grams per 1,000 kilocalories, which is the high end of what cats might consume from commercial foods) and the health of 24 cats. A mere four weeks in, though, the team had to stop the trial because some of the cats exhibited symptoms of vomiting, weight loss, and loss of appetite. Also, 22 of the cats’ kidneys showed changes on ultrasound that were indicative of structural damage and kidney function decline.


So, Dr. Stockman started another study. This time, he gave the cats foods containing 3.6 grams of phosphorus per 1,000 kilocalories. Most of the cats didn’t experience significant differences in the function of their kidneys, but some did experience a gradual rise in urea and creatinine, which are used to measure kidney disease. 


Thanks to these and other studies that have been conducted over the last few decades, it’s become clear that the phosphorus level in cat food needs to be limited, and the good news is the Association of American Feed Control Officials (AAFCO) is planning on voting on a maximum phosphorus level this August, and approval is expected. 


Changes include:


  • A phosphorus maximum of 5 grams per 1,000 kilocalories
  • A limitation on highly soluble phosphorus at 1 gram per 1,000 kilocalories
  • A calcium-to-phosphorus ratio of 1-to-1


It’s important to understand that there are two sources of phosphorus in cat foods. One is inorganic phosphoric salts that are added to the foods for shelf stability and palatability. The other is phosphorus that’s naturally occurring in vegetables and meat. Other nutrients and ingredients, and the solubility of phosphorus, can affect how much of it is absorbed, and phosphoric salts are more bioavailable. Experts also consider the calcium-phosphorus ratio in cat foods.


Therefore, even though the maximum phosphorus level AAFCO will set is higher than the 4.8 grams that caused kidney decline in Dr. Stockman’s study, he said the calcium-to-phosphorus ratio and the limit on highly soluble phosphorus will keep it safe.    


It could take a long time before you see these changes implemented in cat foods, especially if reformulations are needed. If you want to know the amount of phosphorus in your pet’s food, contact the manufacturer.


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Lisa Selvaggio
Lisa Selvaggio

Lisa Selvaggio is a freelance writer and editor, and our resident cats-pert, with certifications in pet nutrition and pet first aid. She enjoys producing content that helps people understand animals better so they can give their pets a safe and happy home.

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