This is by no means a list of everything on the planet that’s bad for cats. But it’s a few of the things that should be avoided by themselves or as an ingredient in something else.
Food is the foundation of health. How long an animal lives and, most important, the quality of its life, depend greatly on the quality and quantity of the food that it eats. Simply put, food is body-fuel, and provides the energy needed for an animal to maintain good health and condition. With regard to nourishment, quantity is not necessarily synonymous with quality. It is very possible for an animal to receive adequate quantities of food and yet still suffer degradation of health due to poor quality ingredients.
Protein. Dietary protein supplies essential amino acids and is needed for the manufacture of antibodies, enzymes, hormones, tissues, and proper pH balance. Protein provides energy for cats and is essential for growth and development. Complete proteins contain ample amounts of essential amino acids and are found in foods such as meat, fish, eggs, and poultry. Incomplete proteins do not provide all essential amino acids and are found in many foods including legumes, grains, and vegetables. Plant proteins don’t supply the essential amino acids that a cat needs, such as taurine which come from animal protein. Cats need protein from animal sources as the amino acids from vegetable sources are not well utilized. Overall, cats have a very high requirement for protein.
So, what's the big deal about food? Why does it have such a huge influence on a body's health? Well, simply put, food is body-fuel. It nourishes each and every cell in the body and creates the energy necessary for life to happen. It's an overly simplified analogy, but food is to living beings like gas is to cars.