There are several commercial foods that are good for both CKD (Chronic Kidney Disease, also called CRF or Chronic Renal Failure) and diabetes. To manage diabetes, you want to feed a low carb (less than 10%) canned food, and to manage the kidney disease, you want to feed a high quality, low phosphorus canned food. Many vets simply recommend low protein prescription diets (like K/D) for cats with CKD, because they are by default low in phosphorus. However, it's the
quality of protein and phosphorus levels that matter, not the protein values. The low-protein prescription kidney diets have
only been shown to be beneficial in end stage renal failure and definitely
should not be fed early stage. In fact, they cause muscle wasting when fed in early stage CKD and are completely inappropriate for an early stage cat--the muscle wasting is more debilitating than the CKD.
Keeping your cat well hydrated is also key in managing CKD, which means NO DRY FOOD. At all. Dry food is moisture depleted and causes chronic dehydration in cats, often the cause of CKD as cats progress in age. Adding a little water with the canned food portions helps, as do pet fountains, since they encourage cats to drink even when they are not thirsty (cats have very low natural thirst drives, so by the time they seek out their water dish they're already dehydrated). See this article on Kidney Disease written by a vet who is an expert in feline nutrition for more information:
http://catinfo.org/#Kidney_Failure.
Here's an updated food list with the values for several premium foods:
https://docs.google.com/leaf?id=0B8...MzhkYTkxOGM4NThk&sort=name&layout=list&num=50. Also see this list (in alphabetical order by brand):
http://catinfo.org/docs/Food Chart Public 9-22-12.pdf, and this list (in order by Phosphorus content):
http://catinfo.org/docs/Food Chart Phosphorus 9-22-12.pdf. You're looking for something with less than 10% carbs (for the diabetes) and less than 250 mg/kcal of phosphorus (for the kidneys). The foods I would suggest are Merrick's Before Grain Beef, Merrick's Before Grain Turkey, Merricks' Cowboy Cookout, Merrick's Surf & Turf, Wellness Turkey, EVO 95% Chicken & Turkey, or Blue Wilderness Duck.
If those are out of your price range the next best thing to feed are the low carb Friskie's Special Diet Turkey & Giblets and Salmon flavors. However, I would
strongly urge a food without byproducts, and keep in mind that they're still cheaper than the prescription foods and usually about the same as many grocery store brands if bought in large cans or in cases. Studies have shown that the quality of the protein source does make a difference in controlling the disease, and that needs to be considered along side phosphorus content.
I know this advice is not what your vet is telling you, but I was in the same boat as you when my Gabby was diagnosed with kidney disease. My vet put Gabby on Purina N/F (at least she got the canned part right), and I watched Gabby waste away--her quality of life was NOT good. Gabby hated the food, and would often refuse it. I then did some reading and realized it wasn't the kidney disease that was making her go downhill, it was the DIET. I switched her to a low phosphorus food with no byproducts, and she did fantastic. In the two and a half years I had left with her after her CKD diagnosis, her kidney values stayed exactly the same (she passed away from cancer, unrelated to her kidney disease). Given that you also have to contend with the diabetes, feeding the prescription kidney diet isn't an option for you. Even if the prescription diet was beneficial (which it isn't), right now the diabetes is the more pressing diet concern. A cat with uncontrolled diabetes is already possibly breaking down its fat and protein stores because it's not properly metabolizing its food, and feeding a moisture depleted, severely low protein diet is a recipe for a potentially deadly complication of diabetes called
diabetic ketoacidosis. If you don't want to argue with your vet, just tell them that your cat is refusing to eat the K/D and take it back for a refund. Most cats hate the taste of it anyway, so it would not be unusual.
Here is a fantastic website with a lot of information about CKD:
http://www.felinecrf.org/
