For renal disease management, it's best to talk to your vet on diet requirements (doesn't mean you need to use the brand he suggests, but what general protein and other nutritent levels to aim for is something he should be able to discuss). High protein doesn't cause kidney problems, but management of existing kidney problems can require modified diet indeed. Of some importance is high quality protein (low quality proteins are stressful to the kidneys) so it makes some sense to watch that you don't end up with a food loaded with plant/grain protein. You might also find this site useful:
http://b-naturals.com/May2004.php
For the other dog though - the one with no kidney problems, but who is overweight: protein does not make dogs fat (not unless overfed, anyway). More often, it is large amounts of
carbohydrates that stack the fat on. Dogs have no evolved need of carbs at all in their diets, being instead uniquely evolved to consume diets comprised primarily of protein and fat. Fat (unless excessive amounts are consumed) gets burnt as instand energy. But carbs? Well, the dog's body doesn't utilise those well, and they're most often just stored as fat. Unfortunately, most so-called diet foods have very little else in them but carbs (the only exception I can think of just now is Canidae Platinum). And interestingly, many people with overweight (fat) pets report weight loss when they switch to high protein/high fat/low carb foods such as Innova EVO.
Anyway, it actually sounds as though you have two dogs with very different dietary needs there. I'm not sure that there would be all that many (if any) products out there that would suit the needs of both a renal patient and an overweight dog.
