These are some foods that should be avoided in cat’s diets:
Tuna can be addictive food to cats, even if that’s a can of human food tuna. If you are treating tuna as snacks, that may be fine. If you are using human form of tuna as a regular diet for your cats, that’s the problem. The human form of tuna does not provide enough nutrients a cat need. This may lead to malnutrition. Too much tuna may also cause mercury poisoning.
Onion can break down a cat’s red blood cell, no matter it is in powdered, raw, cooked or dehydrated forms. Not even baby food that contains onion powders. If your cat accidentally ate a little bit of onion, that should be fine. Consuming a large quantity of onion at a time or feeding your cats with onion regularly may cause poisoning. Onions, chives and garlic can cause gastrointestinal upset to your cat.
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 very smelly diarrhea.
Raw meat and raw fish, including raw eggs may contain bacteria that cause food poisoning to your cats. There is an enzyme in raw fish that can destroy thiamine. Thiamine is an essential material for Vitamin B for your cat. Lacking of thiamine may result in serious neurological problems, may also 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 kinds of butter 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.
Salmonella and E. coli inside raw meat and raw eggs can be harmful to both human and pets. Same as cats, an enzyme in raw eggs decreases the absorption of biotin (a vitamin B). For dogs, this may 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 esophagus usually of smaller dogs. On the other hand, chicken bones of any type are rarely a problem.