If you make it a habit to read the ingredient label before purchasing cat food, there are things to look for and things to avoid. To help point the way to the healthier types of quality cat food, experts and advocates say there are three things to avoid. These are chemical preservatives, meat byproducts, and carbohydrate fillers.

Raising Awareness

Pioneers such as Ann Martin have raised consumer awareness about the ingredients in commercial pet foods, including cat food. Her book "Foods Pets Die For," originally published in 1997, was very influential. Modern crusader Susan Thixton, founder of the website Truth About Pet Food, has taken on the Food and Drug Administration (FDA) and the pet food industry. The site is run by thousands of veterinarians, scientists, and everyday pet lovers who work together to make pet food safe. Thixton is working with Mollie Morrissette and Jean Hofve to give consumers a voice with the FDA and the Association of American Feed Control Officials (AAFCO).

BHT, BHA, and Ethoxyquin

Chemical preservatives like butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA) are very effective at preserving dry cat food but are suspected to be potentially cancer-causing agents. These chemicals are often added to oils and fats. They have been found to cause kidney and liver damage in rats, according to National Center for Biotechnology Information and the National Library of Medicine.

In fact, outside of its purpose as an antioxidant for certain spices, ethoxyquin is illegal to use in human foods in the U.S. and is extremely harmful when directly swallowed or touching the skin. Many pet food manufacturers have moved toward using more "natural" preservatives, such as Vitamin C and E.

Meat Byproducts

The AAFCO defines meat byproducts as the following: "Secondary products produced in addition to the principal product."

Besides not knowing what species of animal the meat comes from, byproducts, as a rule, are considered an inferior form of the protein that cats need. "If we shouldn't eat it, neither should our pets," says Dr. Donna Spector.

There is also meat meal, a mysterious meat byproduct, and concentrate meal. Meat meal and other meals are generally produced by rendering, a process that raises a red flag for cat enthusiasts. Leftovers of meat used in this type of rendering often aren't fit for human consumption. The rendering process alters or destroys natural enzymes and proteins. The meal is a highly-concentrated protein powder that is often low in quality and inferior by nature. Look for higher amounts of named protein sources like chicken and salmon, such as what is in better quality canned cat foods.

Corn Meal and Carbohydrate Fillers

Excess of carbohydrate "fillers" is not good for cats. Dry food can contain as much as 50 percent grain. Older cats and cats with diabetes can be fed grain-free food, as long as the carbohydrate content is limited. Wheat gluten can also be problematic as it's a cheaper alternative to muscle meat protein and whole-grain options. Some pet food can contain melamine, which in combination with cyanuric acid, also found in pet foods, can cause kidney stones and kidney failure, according to the World Health Organization.