Same like with human health many disease processes can be prevented and reversed with proper nutrition.
General rule of a thumb should be "longer the shelf life of the food, shorter the lifespan of your pet".
Here are some links with detailed information for proper start, feel free to continue if you have some good links.
When it comes to our feline companions am delighted I stumbled across this website which contains most comprehensive selection of essential information about feline health care and nutrition I have encountered on the net.
It contains excellent guide to making your own cat food, great deal of information on different medical conditions and vaccines.
Feeding Your Cat: Know the Basics of Feline Nutrition – Common Sense. Healthy Cats.
And as for our canine friends here are some links which contain excessive information on how to organize your dogs diet. Yes dogs need magnesium supplementation too.
This is my favorite veterinarian and his website is a true treasure cove of various information on dog and human health
In case you need to give pills or tablets to your pets this is good to know
A veterinarian discusses the dangers of pilling cats if not followed with food or water. Tips and tricks for pilling cats and dogs safely are discussed.
www.catinfo.org