Yes, dogs can eat ketchup, but keep it in minimal amounts to avoid upset stomachs. Ketchup is highly acidic and loaded with salt and sugar. Dogs may suffer from digestive discomfort, vomiting, and diarrhea when consumed excessively.
Risks
Tomato sauce or ketchup is highly acidic. It also has high sugar and salt content which are unhealthy for dogs.
Ketchup may contain garlic and onion, which can be toxic to dogs in large amounts.
Servings
If your dog has consumed food with a small amount of ketchup in, it is likely he will be ok. However, it is best to avoid giving your dog ketchup or tomato sauce because of its high sugar and salt content.