The human foods that are most dangerous to dogs are chocolate, foods sweetened with the non-caloric sweetener xylitol, bread dough and alcohol, according to the American Society for Prevention of Cruelty to Animals. All of these foods can cause fatal poisoning, as can moldy food of any type.
Dogs can suffer damage to red blood cells from eating garlic, onions and other foods from the onion family. Some dogs tolerate eating a few grapes or raisins, but others have severe reactions, including kidney failure. Macadamia nuts can cause temporary pain and loss of muscular control but are seldom fatal. Home brewers should be careful not to let their dogs eat either fresh or cooked hops, which can cause multiple organ failure.