These are some foods that should be avoided in cat’s diets:
Cats can be addicted to tuna, whether it's packed for cats or for humans. Some tuna now and then probably won't hurt. But a steady diet of tuna prepared for humans can lead to malnutrition because it won't have all the nutrients a cat needs. And, too much tuna can cause mercury poisoning.
Onion in all forms -- powdered, raw, cooked, or dehydrated -- can break down a cat's red blood cells, leading to anemia. That's true even for the onion powder that's found in some baby foods. Eating a large quantity once or eating smaller amounts regularly can cause onion poisoning. Along with onions, garlic and chives can cause gastrointestinal upset.
A lot of cat owners like to offer cats with dairy products, like milk, eggs. Many cats are lactase deficient so cannot break down lactose, and then it acts like a laxative. The result can be a very smelly diarrhea.
Raw meat and raw fish, like raw eggs, can contain bacteria that cause food poisoning. In addition, an enzyme in raw fish destroys thiamine, which is an essential B vitamin for your cat. A lack of thiamine can cause serious neurological problems and lead to convulsions and coma. Again, the occasional feed is no problem, but a prolonged diet of raw fish will cause thiamine deficiency in cats.
There is also an amount of food that dogs owners should be aware of.
First, Xylitol is a type of artificial sweetener found in many sugar-free products, like gum and candy, as well as some nut butters like peanut butter. Xylitol can cause insulin release, which can lead to liver failure, seizures and brain damage.
While many dog owners are already familiar with the chocolate warning, coffee and caffeine all contain substances called methylxanthines, which in high doses are very dangerous to a pet's health.
If methylxanthines and caffeinated are eaten by pets, they can cause vomiting and diarrhea, panting, excessive thirst and urination, hyperactivity, abnormal heart rhythm, tremors, seizures and even death. The darker the chocolate the more poisonous it is. White chocolate has no methylxanthines; milk chocolate has a moderate amount, while baking chocolate contains the highest.
Grapes are also poisonous to some dogs (there seems to be a genetic basis to this), and the mechanism is not clear as to why they are poisonous. In some cases very small amounts of raisins being ingested has caused severe illness.
There is a chance that raw meat and eggs may contain bacteria such as Salmonella and E. coli, which can be harmful to both pets and humans. Raw eggs also contain an enzyme called avidin that decreases the absorption of biotin (a B vitamin), which can lead to skin and coat problems, but it takes a lot of ingesting of raw eggs to have this effect.
While many owners consider dogs to be fond of bones, bones can also be a problem for pets, especially if cooked. This is because heating coagulates the proteins in the bone, and makes them indigestible. Raw bones are broken down by the acid in the stomach, whereas cooked bones are not. Dogs and cats have evolved to deal with sharp bones going through their intestinal tract, and have an extra thick layer in their gut. However, the main thing that can be an issue is cooked chop bones getting stuck in the oesohagus usually of smaller dogs. On the other hand, chicken bones of any type are rarely a problem.