The studies aren't specific to raw, rather, they're saying that low-protein diets don't really work for cats with renal disease (and IMO, they don't work for ANY cat because cats are obligate carnivores. But that's a different thread.
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Protein is needed for all blood cells (white and red). The body is made of protein. If a cat is not getting enough (animal) protein in it's diet, it's body will start breaking down it's own muscles in order to survive. That's when you see muscle wasting and weight loss. Basically, the cat is starving.
This is from Dr. Pierson's site,
www.catinfo.org:
Kidney Disease (CKD - formerly called "CRF"): Chronic kidney disease is probably the leading cause of mortality in the cat. It is troubling to think about the role that chronic dehydration may play in causing or exacerbating feline kidney disease.
And remember, cats have a less than optimal water balance - especially CKD cats that are losing a lot of water via their 'leaky' kidneys - when they are on a diet of predominantly dry food. The prescription dry 'renal diets' such as Hill's k/d - which are commonly prescribed by veterinarians - contain only a small amount of moisture (~10% versus 78% for canned food) leaving your cat in a less than optimal state of water balance.
I have no other word for dry 'renal' diets other than "atrocious" given their water-depletion, low protein amount, and the low biological value of the protein (plant vs animal-based) that they are comprised of. I would have to be stranded on a desert island with no other food source before I would ever consider feeding these diets to any cat in my care.
Regarding hydration, I must say that I find it truly amazing when I hear about the very large numbers of cats receiving subcutaneous fluids while being maintained on a diet of dry food. This is an extremely illogical and unhealthy practice and every attempt should be made to get these cats on a diet that contains a higher moisture content.
Please also note the following list of the first four ingredients of Hill's dry k/d after reviewing this section on reading a pet food label - and bearing in mind that your cat is a carnivore.
This diet (or any other dry 'renal' diet) would never find its way into a food bowl owned by any cat in my care.
The first three ingredients are not even a source of meat and the fourth ingredient is a by-product meal which is not necessarily an unhealthy source of protein but it would be nice to see some muscle meat ("chicken") in this product.
Brewers rice, corn gluten meal, pork fat (preserved with mixed tocopherols and citric acid), chicken by-product meal
The purpose of this 'prescription' diet is to restrict protein which, unfortunately, it certainly does. However, please understand that there are no studies showing that restricting protein to this level will prevent further deterioration of kidney function.
'Renal' diets restrict protein to the point that many cats - those that are not consuming enough of the diet to provide their daily protein calorie needs - will catabolize (use for fuel) their own muscle mass which results in muscle wasting and weight loss.
This internal breakdown of the cat’s own muscle mass will cause an increase in creatinine (and BUN) which needs to be cleared by the kidneys. The rise in creatinine and BUN, and muscle wasting, can lead to an often-erroneous conclusion that the patient’s CKD is worsening.
Of course, the same deterioration can occur in any cat that is not consuming enough protein, but the level of protein in these diets is not only at an extremely low level, it is in an incomplete form for a carnivore. Note that they are often made up mainly of plant proteins - not meat proteins - especially the dry versions.
I hope this helps, and I hope Jemma pulls through! Sending purrs and hugs to you and Jemma.