If a dog eats cat food will it damage his kidneys?

No, not if it's only done once in awhile, but cat food should never be fed to a dog as part of their main diet.

Cat food is significantly higher in protein than dog food. It is important to not feed a dog cat food over a long period of time. Scientists have spent a lot of time studying what each animal needs in their diets and the foods are formulated to meet these requirements. The high levels of protein can worsen kidney problems in dogs with such problems if they are fed the cat food for a long period of time. Our puppy loves cat food and we had to place the cat food bowl on a tray that the cats could jump to but the dog couldn't to stop the dog from eating it all the time.

IAMS is a very poor quality food. If you read the ingredients, the majority are ingredients that dogs should not be fed. Any sort of wheat, soy, corn or by-products should be avoided. There have been scientific studies showing that these ingredients plus many others are shown to cause cancer in the future. (Many dogs actually have an allergy to corn or corn by-products as well as to wheat and soy.) If you are looking for a healthy, dog food, approved for human assumption try Solid Gold or Natural Balance. They are very high quality foods and you will never have to worry about recalls.