Special 'renal' diets are often prescribed for cats with chronic renal failure (CRF). There is now plenty of good scientific evidence to show that CRF cats eating these diets live longer (on average twice as long) as those not fed the diets. The diets should be introduced gradually to encourage acceptance by the cat. Renal diets are formulated to contain:
Waste products are produced by the body as protein is converted into energy. So, by reducing the amount of protein in the diet, so the amount of waste needing to be processed by the ailing kidneys can be limited or reduced. This in turn can reduce the clinical signs associated with the build up of waste products in the body (called uraemic signs), such as vomiting, loss of appetite, anaemia and lethargy. The benefits of protein restriction in reducing these clinical signs have been supported by scientific studies performed both in cats and other species.
Whether dietary protein restriction actually has any impact on the progression of renal failure in cats is still a very controversial area. As nephrons within the kidney fail, the smaller number of remaining nephrons adapt to deal with the greater waste processing load placed on them. In some experimental studies, these adaptive changes have been demonstrated to be harmful to the remaining nephrons, and ultimately cause or contribute to the progression of CRF. In experimental models, restricting dietary protein has been shown to minimise these changes and thus slow the progression of CRF. At this stage, however, this benefit is only suggested (not proven) in humans, and there is no proof that cats would benefit in the same way.
Phosphorus is an important mineral usually found in nature combined with oxygen as phosphate. Whilst an important component of cells and bone in the mammalian body, too much phosphate contributes towards hyperparathyroidism (over production of parathyroid hormone which regulates the amount of calcium and phosphorus in the body). In one scientific study looking at cats with naturally occurring renal disease, improved survival times were seen in those fed a phosphate restricted diet (Elliott et al, JSAP 2000, 41: 235 -242).
Increased potassium and vitamin B
Prescription renal diets are supplemented with potassium and water soluble vitamins (B and C vitamins) which CRF cats are vulnerable to losing in their urine. Potassium deficiency is covered in greater depth in the section: Managing potassium deficiency.
Renal diets usually have lower levels of sodium, which may help to reduce the risk of systemic hypertension (high blood pressure) from developing.
Palatability and calorie content
Increased palatability and calorie density helps CRF cats with a poor appetite to maintain a normal body weight.
Renal diets are formulated to help prevent acidosis (excess blood acidity - a common consequence of kidney disease) from developing in cats with CRF.
Additional dietary manipulations
Renal diets often have supplemented fibre which helps to reduce absorption of protein breakdown products across the bowel. Levels of fatty acids (e.g. omega 3 polyunsaturated fatty acids) are also often supplemented as this has been shown to slow the progression of renal disease in other species.