The European pet food industry federation (FEDIAF) publishes the most accurate, science-backed information regarding food toxicity in pets. They state that dogs and cats should not consume four foods: Grapes (and raisins), Cocoa (chocolate), Macadamia nuts (no known toxin identified, but can cause GI upset), and members of the onion family, including chives, leeks, shallots, and large amounts of gavage-fed garlic extract (not fresh garlic).
So why do so many pet websites say not to feed nuts and seeds, herbs, spices and teas, peaches, cherries, avocadoes, and many other healthy foods? Because many foods can be a choking risk if pits/rinds/husks aren’t removed, and all foods can create digestive upset if consumed in large quantities, use some common sense when feeding and treating pets: wash produce and try to buy organic or spray-free foods, feed only the edible parts of foods to all your family members (no cores, pits, etc).