Foods to avoid

The following foods have been shown to be toxic to dogs. How much of them would be needed to do harm is usually dependent on the size of your dog.

Chocolate
Chocolate contains an ingredient called theobromine that is toxic to dogs and, if eaten in large enough amounts, can be fatal. The darker the chocolate is, the higher the theobromine content is. Symptoms of poisoning occur when a dog has eaten 45 mg per pound of body weight; death has been known to occur when 52 mg per pound of bodyweight has been ingested.
Milk chocolate contains about 44 mg per ounce, while dark baking chocolate contains about 390 mg per ounce. You can see from this that it wouldn’t take much of a dark chocolate to kill a small dog. Once the chocolate has been eaten, there is no antidote for the overdose of theobromine.

Coffee, Tea and Cola All contain caffeine which is toxic to dogs in large quantities. Caffeine has been shown to be toxic at levels of 63 mg per pound of bodyweight

Onions
Onions contain a substance called n-propyl disulfide which can damage red blood cells. It is in fresh, dried, cooked and powdered onions. If a large amount is ingested, or even if smaller amounts are fed over a long period of time, the dog can develop an anemia called Heinz body anemia. If left untreated, it can be fatal. If diagnosed, it can usually be reversed by blood transfusion.

Garlic
Garlic contains the same substance as onions. A little bit in the food, or a sprinkle of powder occasionally probably won’t do any harm, but since it does contain the same anemia-causing agent, it should be used with care. Toxic amounts for onions and garlic are not known, so both should be used very sparingly, if at all.

Grapes and Raisins The ASPCA has had about a dozen cases reported of dogs suffering toxic reactions or dying after eating large quantities of grapes or raisins.
The actual substance in the grapes or raisins that caused the deaths hasn’t been identified, but it causes renal failure. A general toxic amount is not known at this time, but death did occur after one dog ingested 1 ounce of fruit per kilogram (2.2 pounds) of bodyweight.
A dog would presumably have to eat fewer raisins, being a more concentrated form of grapes, to cause problems. Macadamia Nuts While rarely fatal, the ingestion of macadamia nuts can cause serious symptoms including vomiting, tremors, abdominal pain, lameness and joint stiffness. The quantity known to cause problems is .9 g per pound of body weight.

Green Potato Flesh and Skins
If the skin or flesh of a potato is green, it contains a substance called solanine. This can be toxic, even in small quantities, so always peel off or cut away any green parts. Ingestion of this can cause a myriad of symptoms involving the whole body .