The Second among the list is onions, you should be extremely careful with food that contain onions. Onion powder and garlic are some of the foods that can cause havoc to your dogs. All kinds of onion and garlic are a problem. This comprises of raw, dehydrated, cooked, powders or those in foods. Onions can break down dog’s red blood cells and drastically decrease the oxygen that gets in its blood. Although the problems might not show up right away, they can build up over time. Look out for symptoms like vomiting, loss of appetite, diarrhea, and a general malaise.