Phosphorus in Feline Nutrition: What AAFCO's New Phosphorus Recommendations Mean for Cat Food Formulation
RESEARCH & DEVELOPMENT - TECHNICAL POSITION PAPER
Leading with Technical Expertise - White Paper
Leah Lambrakis, Department of Technical Services
Phosphorus is an essential nutrient for cats, with roles that extend throughout the body. Together with calcium, it provides the mineral foundation for bones and teeth, while also playing important roles in normal cell function and energy use. Considering how phosphorus is so important, the body regulates its concentration closely. The kidneys play a central role, adjusting the amount of phosphorus retained or excreted in response to dietary intake and the body's needs. This regulation is coordinated through a network of hormones, which collectively help maintain the balance among phosphorus, calcium, bone and kidney function. ¹
Calcium and phosphorus are also closely connected. Bone serves as the body's primary reservoir for both minerals, and changes in the intake or metabolism of one can influence the other. For this reason, feline nutrition has long considered not only whether diets provide adequate amounts of calcium and phosphorus, but also the relationship between them, commonly expressed as the calcium-to-phosphorus, or Ca:P, ratio.
As our understanding of feline mineral metabolism has advanced, researchers have increasingly explored the other side of the nutritional equation: whether the amount of phosphorus consumed, the source from which it comes, and its relationship with dietary calcium may also influence long-term health.
Over the past decade, a growing body of research has examined phosphorus intake in healthy cats from several perspectives. Researchers have studied diets containing different concentrations of phosphorus, compared naturally occurring and added inorganic phosphorus sources, evaluated differences in phosphorus solubility and availability, and investigated how the Ca:P ratio may modify the physiological response.¹² Together, this work shifted the scientific conversation beyond phosphorus requirements alone and helps explain the recent changes to the AAFCO Cat Food Nutrient Profiles. ³
From Emerging Science to AAFCO Review
For many years, phosphorus recommendations in cat food focused primarily on providing enough of this essential mineral to meet a cat’s nutritional needs.⁴ As new research emerged, scientists began asking if there could also be consequences associated with feeding too much phosphorus, particularly when certain phosphorus sources are used.
Early work by Dobenecker and colleagues evaluated healthy adult cats fed diets containing higher levels of phosphorus.⁵ The researchers observed changes in several indicators of kidney health and phosphorus metabolism, raising questions about the potential effects of high phosphorus intake in otherwise healthy cats. Research by Alexander and colleagues added another important observation.⁶ Cats fed a diet containing a high concentration of phosphorus, much of it supplied from inorganic phosphate sources, along with a low Ca:P ratio, developed changes in kidney structure and markers of kidney function. These studies suggested that the story is more complex than total phosphorus alone. Further, an evaluation of 82 commercially available cat foods found considerable variation in phosphorus concentration and Ca:P ratio, demonstrating that phosphorus levels relevant to the emerging research were also present in the marketplace.⁷
Researchers then began looking more closely at the source of phosphorus. Phosphorus occurs naturally in meat, bone and other ingredients used in pet foods. It may also be added through mineral phosphate ingredients for nutritional or functional purposes. These different sources can vary considerably in how readily phosphorus becomes available to the animal. Research by Coltherd and colleagues also demonstrated that different phosphorus sources produced different responses in cats, leading to an important concept: not all dietary phosphorus behaves in the same way.⁸
As this body of research grew, AAFCO was asked to consider whether the existing Cat Food Nutrient Profiles still reflected the current scientific understanding of calcium and phosphorus nutrition. In 2024, AAFCO convened an expert panel to review the emerging literature and determine whether updates to the calcium and phosphorus recommendations for cat foods were warranted.⁹ The panel brought expertise in companion-animal nutrition, nutrient requirements, feline renal physiology, diet formulation and the development of AAFCO nutrient profiles. The panel reviewed research examining total phosphorus intake, inorganic phosphorus sources, phosphorus availability and solubility, calcium-to-phosphorus balance, and indicators of kidney and mineral health in cats.⁹
Translating the Science in the New Recommendation
Following its review of the available research, the AAFCO Expert Panel recommended updates to the Cat Food Nutrient Profiles that consider three important aspects of phosphorus nutrition: the total amount of phosphorus in the diet, the contribution from highly soluble phosphorus sources, and the balance between calcium and phosphorus.⁹ The Expert Panel concluded that phosphorus from a variety of sources has been safely fed to adult cats at concentrations up to 5 g/1,000 kcal ME when highly soluble phosphorus contributes less than 1 g/1,000 kcal ME and calcium and phosphorus are maintained at a ratio of at least 1:1.³
The 2026 AAFCO Official Publication includes the following recommendations for cat foods:
| Nutrient | AAFCO Cat Food Nutrient Profile |
|---|---|
| Maximum total phosphorus | 5 g P/1,000 kcal ME |
| Highly soluble phosphorus | <1 g P/1,000 kcal ME, included within total phosphorus |
| Minimum Ca:P ratio | 1:1 |
These recommendations recognize that dietary phosphorus should be evaluated in the context of phosphorus source and calcium balance, not total phosphorus alone.
What Is Highly Soluble Phosphorus?
An important part of the new recommendations is the introduction of a limit specifically for phosphorus from highly soluble sources. The Expert Panel identified highly soluble phosphorus sources based on their behavior in water.⁹ Phosphate salts that are greater than 80% soluble after one minute of exposure to water are considered highly soluble, for purposes of the recommendation. ⁹ These include certain sodium phosphate ingredients commonly used in pet food formulation. Phosphorus naturally present in ingredients such as meat and bone is incorporated within the food matrix and generally has lower water solubility than highly soluble inorganic phosphate salts. Some added phosphate salts dissolve much more readily, making the phosphorus rapidly available for absorption.¹⁸ This distinction is important for pet food formulation. Two foods with the same total phosphorus concentration may have very different contributions from highly soluble phosphorus sources. Understanding both the amount and the source of phosphorus therefore becomes an important part of formulating cat foods within the new recommendations.
Formulation Application
Translating the new calcium and phosphorus recommendations into finished cat foods adds another layer of complexity for pet food formulators. Meeting the new framework requires consideration of not only how much phosphorus is present in a formula, but where that phosphorus comes from and how it is balanced with calcium. This can be particularly complex in wet pet food. Wet foods often contain a diverse mix of animal-derived ingredients, including muscle meats, organs and bone-containing materials. Each contributes naturally occurring phosphorus and calcium to the formulation, and the amounts can vary depending on the ingredient, raw material composition and supplier specifications.
Phosphate ingredients can serve multiple purposes as well. In addition to contributing phosphorus, certain phosphates may be used for their functional properties in food manufacturing, including their effects on water binding, meat restructuring, and texture. Under the new recommendations, the phosphorus contributed by highly soluble phosphate sources must now be considered within its own limit while still contributing to total dietary phosphorus. This creates a complex formulation challenge. Reducing a highly soluble phosphate may affect more than the mineral profile. Replacing one phosphorus source with another can influence calcium balance or functionality. Changing animal-derived ingredients to manage total phosphorus may affect protein, fat, ash, texture, palatability and product cost. Further, increasing calcium simply to achieve the desired Ca:P ratio may create additional nutritional or product-performance considerations. For formulators, calcium and phosphorus can no longer be viewed as two independent nutrient specifications checked at the end of formulation. They must be considered as part of the ingredient and product design from the product concept.
Closing: Providing Time for Industry Transition
While the updated calcium and phosphorus recommendations represent an important advancement in feline nutrition, implementing them across the pet food industry will require time. Existing cat food formulations may need to be evaluated or reformulated, ingredient and supplier specifications reviewed, and product labels updated.
At the 2026 AAFCO Annual Meeting, the membership approved a recommendation providing enforcement discretion for the updated cat food calcium and phosphorus requirements through 2030. This timeline aligns implementation with AAFCO’s Pet Food Label Modernization (PFLM) transition period, allowing manufacturers to address formulation and labeling changes together as products move to the new requirements. The additional transition time is particularly important given the complexity of the new phosphorus framework.
The enforcement discretion period provides the industry an opportunity to build the ingredient knowledge, formulation tools, process capability and product data needed to implement the new recommendations consistently, while continuing to advance the science surrounding phosphorus nutrition in cats.
Our Commitment – Leading with Technical Expertise – we are here to provide guidance and insights – do not hesitate to connect with us at Simmons Pet Food, petcomments@simfoods.com. We would love to hear from you and be part of your pet’s nutrition solution!
Literature Referenced
Laflamme D, Backus R, Brown S, Butterwick R, Czarnecki-Maulden G, Elliott J, Fascetti A, Polzin D. A review of phosphorus homeostasis and the impact of different types and amounts of dietary phosphate on metabolism and renal health in cats. J Vet Intern Med. 2020;34(6):2187–2196.
Stockman J. Dietary phosphorus and renal disease in cats: where are we? J Feline Med Surg. 2024;26(10):1098612X241283355.
Association of American Feed Control Officials (AAFCO). 2026 Official Publication. Association of American Feed Control Officials; 2026. Cat Food Nutrient Profiles.
National Research Council. Nutrient Requirements of Dogs and Cats. Washington, DC: The National Academies Press; 2006.
Dobenecker B, Webel A, Reese S, Kienzle E. Effect of a high phosphorus diet on indicators of renal health in cats. J Feline Med Surg. 2018;20(4):339–343.
Alexander J, Stockman J, Atwal J, Butterwick R, Colyer A, Elliott D, Gilham M, Morris P, Staunton R, Renfrew H, Elliott J, Watson P. Effects of the long-term feeding of diets enriched with inorganic phosphorus on the adult feline kidney and phosphorus metabolism. Br J Nutr. 2019;121(3):249–269.
Summers SC, Stockman J, Larsen JA, Zhang L, Rodriguez AS. Evaluation of phosphorus, calcium, and magnesium content in commercially available foods formulated for healthy cats. J Vet Intern Med. 2020;34(1):266–273.
Coltherd JC, Staunton R, Colyer A, Thomas G, Gilham M, Logan DW, Butterwick R, Watson P. Not all forms of dietary phosphorus are equal: an evaluation of postprandial phosphorus concentrations in the plasma of the cat. Br J Nutr. 2019;121(3):270–284.
AAFCO Calcium/Phosphorus Expert Panel. Report to the AAFCO Pet Food Committee with Recommendations for Changes to the AAFCO Cat Food Nutrient Profiles and Mineral Ingredients Definitions to Avoid Nutritional Phosphorus-Induced Renal Disease in Cats. Association of American Feed Control Officials; 2024–2025.