“This does become a complicated area of nutrition, a cat is an obligate carnivore as unlike most animals a cat cannot synthesise taurine so has to eat meat. Cereals are used in commercial cat food and will certainly not harm a cat and have nutritional benefits as long as there is enough meat content . The cheapest the cereal the harder it is for any animal to digest and therefore a rice based food is far more digestible.
Cats also have a tendency to produce stones in their urinary tract and an acid urine will dissolve these. It is therefore important to ensure the diet does not contain too much of the wrong minerals that can change the urine PH , magnesium being the worst which is present in a lot of farmed chickens.”

I didn’t know about the urine pH issue but there are similarities in humans: urinary tract infections with urease-producing bugs like Proteus or Pseudomonas – the urease metabolises urea into ammonia and carbon dioxide. This is problematic as the NH3 raises pH which causes formation of struvite stones. These are composed of a combination of magnesium ammonium phosphate (struvite) and calcium carbonate-apatite. As pH rises the phosphate becomes less soluble.