There seems to be debate in the chronic kidney disease (CKD) community regarding renal diets, their effectiveness of increasing longevity, and when to introduce them.
Pro-renal diet studies:
More cautious renal diet studies:
My interpretation is that traditional, older research does pretty strongly support an increase in longevity for cats being fed a renal diet. Cats are so complex though, and often our older cats can have concurrent conditions. The newer research seems strongly in favor of the body condition markers playing a big role in increasing longevity. So, we’ve got conflicting information. I wonder if some of the cats in these studies didn’t take well to the renal food, with nausea or just flat out not liking it as much, decreasing their overall caloric intake contributing to the results. There’s probably a happy medium in here somewhere. What about cats that are overweight to begin with? In theory, they could afford to lose a little in the physical department if that means reducing the load on the kidneys. If your cat is otherwise healthy, and early stage CKD, maybe you could find a middle ground. Potentially a food with lower protein content, but not as drastic with the restriction. As this community grows, it will be interesting to get some more input from folks with opinions and experience related to this topic.
Pro-renal diet studies:
- Polzin et al., 2000, from the University of Minnesota
- Endorses renal diets as a mainstay for managing CKD. The general idea is to introduce a renal diet (restrict protein, phosphorus, and sodium) in early stage CKD rather than waiting for the end stages. No discussion about concerns or limitations of this diet and over-restriction.
- Ross et al., 2006, from the University of Minnesota
- Specifically looked at Stage 2 and Stage 3 CKD cats. Only 45 cats were in the study. Significant reduction in renal-related deaths was found in cats being fed the renal diet, while “significant differences” were not detected in body weight and other key markers. Some concerns about the cats in the two test groups and their other medical conditions, potentially skewing some results.
- Platinga et al., 2000s, from Utrecht University, the Netherlands
- Retrospective study that about cats fed traditional diets and renal diets, finding that renal diets roughly doubled median survival time, but with considerable variation depending on the diet. No data on adverse effects of kidney diets and nothing on body condition with no record of daily food intake details.
More cautious renal diet studies:
- Machado et al., 2022, from the University of Sao Paulo, Brazil
- Focus on Stage 1 and Stage 2 CKD cats and the impact of feeding a low-phosphorus maintenance protein diet. The study was completed with 25 cats over 60 days. Statistical analysis was used to look at body weight, muscle mass score, and body condition score. The biggest result was cats in Stage 2 did show a "significant" reduction in these body markers, not so much in healthy cats and Stage 1 cats. It does appear kidney markers such as SDMA and creatinine did decrease in most cats being fed this diet. Concerns about study size and no discussion about longevity related to these body markers.
- Scherk, 2020s, from Feline Practice in Vancouver, Canada
- Discussion on optimizing the benefits of a renal diet but preventing further muscle wasting. The loss of lean body mass has “profound” effects on survival. Does seem to support renal diet in middle stage CKD with careful monitoring.
- International Renal Interest Society (IRIS) treatment recommendations
- Talks about phosphate control being key, protein restriction also but to be wary of malnutrition, nausea, etc.
My interpretation is that traditional, older research does pretty strongly support an increase in longevity for cats being fed a renal diet. Cats are so complex though, and often our older cats can have concurrent conditions. The newer research seems strongly in favor of the body condition markers playing a big role in increasing longevity. So, we’ve got conflicting information. I wonder if some of the cats in these studies didn’t take well to the renal food, with nausea or just flat out not liking it as much, decreasing their overall caloric intake contributing to the results. There’s probably a happy medium in here somewhere. What about cats that are overweight to begin with? In theory, they could afford to lose a little in the physical department if that means reducing the load on the kidneys. If your cat is otherwise healthy, and early stage CKD, maybe you could find a middle ground. Potentially a food with lower protein content, but not as drastic with the restriction. As this community grows, it will be interesting to get some more input from folks with opinions and experience related to this topic.