Just because your dog enjoys kitty's food doesn't mean you should indulge him. Many dogs abandon their own bowls and attempt to scarf down the cat's food because the fatty content makes it more appealing. Plus -- appeal factor aside -- dogs being dogs, if there's food available they'll eat it. An occasional nibble of cat food won't hurt your dog, but long-term consumption can result in nutritional imbalances and gastrointestinal complications.

The caloric density and high-fat content in cat food aren't suitable for dogs. Dogs that consume cat food are more likely to experience gastrointestinal distress, obesity and disease. Chronic gas, vomiting and diarrhea are common reactions to short- and long-term consumption, as is pancreatitis, which can be life-threatening and turn into a recurring problem. Obese dogs are at higher risk for heart disease, hypertension, cancer, respiratory issues, bone and joint problems, diabetes and bladder stones.

Protein is absolutely vital for the health of dogs and cats. However, cats, as carnivores, require higher protein levels than dogs, who are omnivores. Some cat foods contain protein levels that exceed even the highest-protein dog foods. How harmful those excess protein levels are is the subject of much debate. While excess protein in dogs' diets was previously linked to kidney disease, those studies have been widely discredited. Nonetheless, for your dogs' long-term, optimum health, it's wise to offer him foods that have been specifically balanced for canine nutritional needs.

Dogs and cats have different vitamin and mineral requirements. Most commercial cat foods contain additives that dogs don't need, such as vitamin A, B-complex, arachidonic acid, arginine and taurine. While cats absolutely need the added vitamin A, too much vitamin A can cause bone and joint pain in dogs, according to the ASPCA. The other additives may not be toxic, but long-term consumption of improper nutrient levels can lead to nutritional imbalances. Bottom line: for optimal weight, metabolic function and organ function, feed your dog food that is specifically balanced for the canine system.