Our body eating our own fat.

I understand the concept of allowing our ourselves to “dine in” when we get hungry so that the body can get its energy from our fat stores. This totally works. But what if you are really skinny and don’t have much fat on your body. How does that work? Will you need to give yourself more food than an overweight person? And should a skinny person make sure they eat right away when they are hungry since they don’t have much fat to dine in on?