The following is a list of foods that cats should never eat !!

1. Onions, Garlic, & Related Root Vegetables

Onions contain a substance (N-propyl disulphide) which destroys red blood cells in the cat, causing a form of anemia called Heinz body anemia. Garlic contains a similar substance in a lesser amount.

2. Green Tomatoes, Green (raw Potatoes)

These foods are members of the Solanaceae family of plants, which includes the Deadly Nightshade, and contain a bitter, poisonous alkaloid called Glycoalkaloid Solanine, which can cause violent lower gastrointestinal symptoms. The leaves and stems are particularly toxic. (Tomatoes in pet foods are ripe, and should cause no concern because they appear in relatively small amounts).

Definition Nightshade vegetables: members of the solanaceae family of plants, include potatoes, peppers, eggplants and tomatoes. These plants contain alkaloids that have a potentially inflammatory effect on the body, and should probably be avoided by anyone suffering from arthritic or autoimmune conditions.

3. Chocolate

It's becoming more widely known that chocolate is very toxic to both cats and dogs. Theobromine is the offending substance here. Janet Tobiassen Crosby, D.V.M. has an excellent article on the symptoms, effects, and treatment of chocolate toxicity.

What makes chocolate toxic, anyway?
Chocolate is made from the fruit (beans) of the cacao tree. Theobromine, a component of chocolate, is a toxic compound in chocolate. Caffeine is also present in chocolate and a toxic component, but in much smaller amounts than Theobromine. Both Theobromine and Caffeine are members of a drug class called Methylxanines.

Theobromine and caffeine effects on the body:

• Central Nervous System (CNS) stimulant
• Cardiovascular stimulant
• Increase blood pressure (mild)
• Nausea and vomiting

Why isn't chocolate toxic to humans?
Humans can break down and excrete Theobromine much more efficiently than dogs. The half life of Theobromine in the dog is long; approximately 17.5 hours.

Are some chocolates more toxic than others?
Yes. Unsweetened (baker's) chocolate contains 8-10 times the amount of Theobromine as milk chocolate. Semi-sweet chocolate falls roughly in between the two for Theobromine content. White chocolate contains Theobromine, but in such small amounts that Theobromine poisoning is unlikely. Caffeine is present in chocolate, but less than Theobromine.

Quick Guide for Theobromine levels in different types of chocolate:
From The Merck Veterinary Manual, here are approximate Theobromine levels of different types of chocolate:

• Dry cocoa powder = 800 mg/oz
• Unsweetened (Baker's) chocolate = 450 mg/oz
• Cocoa bean mulch = 255 mg/oz
• semisweet chocolate and sweet dark chocolate is = 150-160 mg/oz
• Milk chocolate = 44-64 mg Theobromine per oz chocolate
• White chocolate contains an insignificant source of methylxanthines.

4. Grapes and Raisins

These foods' toxicity has mainly been found in dogs, in quantities of varying amounts. The ASPCA advises: "As there are still many unknowns with the toxic potential of grapes and raisins, the ASPCA Animal Poison Control Center advises not giving grapes or raisins to pets in any amount." That's good enough for me.

5. Milk

Although milk is not toxic to cats, it may have adverse effects. Simply put, adult cats fed a nutritious diet don't need milk, and many cats are lactose-intolerant, which means that the lactose in milk and milk products produces stomach upset, cramps, and gassiness. If your cat loves milk, and begs for it, a small amount of cream may be okay, two or three times a week. (The more fat in the milk, the less lactose.) Another compromise is CatSip, a product made from skim milk with an enzyme added that helps the digestion of lactose. Catsip is available in supermarkets such as Safeway, Albertson's and A&P, as well as pet products chains, such as PetSmart and Petco.

These are the most commonly seen "people foods" that are potentially harmful to cats. The bottom line is to feed your cat nutritious food developed with his needs in mind and choose treats designed for cats instead of table scraps.

By Franny Syufy, About.com Guide