Ability to add a negative item

This would be huge, as any time I enter something like a restaurant meal but I don't eat one small thing, it becomes a pain to have to create a custom food and try to re-calculate what the new custom food would be. E.g. if I eat a "McDonald's, Double Cheeseburger" as searched for on the app, but don't eat the bun, I could simply add a "negative" item for a hamburger bun, if that makes sense. Also would be great for a meal that includes a side I don't eat.