Many foods that humans eat, especially plant foods (onions, grapes/raisins, macadamia nuts) or foods extracted from plants, such as chocolate and coffee, etc. are harmful to dogs and other animals. The reason is probably that some enzymes present in the digestive tract of humans, are not activated nor present in animals.
Here follows a list of the Top 12 Human foods that are potentially posionous for dogs:
Chocolate: the substance (toxin) in chocolate that is poisonous to dogs is called Theobromine. It is found in chocolate, cocoa beans and cocoa bean hulls. The higher the content in cocoa the more toxic, so dark chocolates are more poisonous to your dog than milk chocolates. Toxic doses of chocolate can cause increased heart rate or irregular heartbeats, restlessness, kidney failure and death. The toxic dose is dependent on weight, so little dogs are at higher risk, but with the high cocoa products now even bigger dogs are at risk. Severe signs occur around 20 mg/lb and seizures and possible death can occur after ingestion of 27 mg of theobromine per pound of body weight. Since milk chocolate contains 58 mg/oz of theobromine, this means a dose of less than 1 oz of milk chocolate per pound of body weight could potentially cause death. Theobromine remains in the dog's system for a long time, so chocolate poisoning can occur even if smaller amounts of chocolate are fed repeatedly over a longer period of time.
Onions: Contain thiosulphate, which can damage red blood cells and cause anemia. Garlic can be toxic, too, but only in large amounts. Thiosulphate levels are not affected by cooking or processing. Raw, cooked, or onion powder are all equally poisonous to dogs. Garlic and garlic powder can have several effects, but the dose needed to induce these effects would be very large. Served in very small amounts garlic can be helpful as a natural anti-flea product.
Human vitamin supplements: many of these contain iron that can damage the lining of the digestive system and be toxic to the other organs including the liver and kidneys.
Liver: when served in large amounts, because it contains too much Vitamin A, which may affect muscles and bones.
Grapes and raisins: causes vomiting, diarrhea, lack of appetite, lethargy, or abdominal pain and have also been found recently to induce kidney failure in some animals. The intensity of the signs is not related to the volume ingested. Some animals may not present any signs if grapes are served only in very limited amounts and on a very infrequent basis. However, given the potential serious risk it is wise to remain on the safe side and not feed your dog any grapes and raisins at all.
Milk: may cause diarrhea, as many adult dogs have insufficient amounts of the enzyme lactase, which breaks down the lactose in milk. Choose lactose-free milk products for your dog.
Avocado: leaves, seeds, stem, skin are toxic. In birds, it produces lethargy, anorexia, breathing difficulties and sudden death. In rabbits, goats, cattle and horses there can be inflammation of mammary glands and fluid accumulation around the heart. The toxic dose in dogs is unknown.
Broccoli: only toxic if fed in very large amounts (over 10% of your dog's diet. Can cause intestinal irritation.
Tomato leaves and potato leaves and stems: are considered toxic because they contain oxylates, which can affect the gastrointestinal, nervous, and urinary systems. The largest amount of oxylates are found in the leaves, but the fruit (tomato) itself also contains some.
Macadamia nuts - Contain an unknown toxin, which can affect the digestive and nervous systems and muscle. Can cause a tremor of the
skeletal muscles, and weakness or paralysis of the hindquarters. These symptoms are usually temporary.
Pips and Kernels: the pips of pears and apples, and the kernels of plums, peaches and apricots contain cyanogenic glycosides resulting in cyanide posioning and the larger kernels can also cause obstruction of the digestive tract.
Candy containing the sweetener Xylitol