If you are underweight because you are not a fan of food (as you put it), and your doctor has even diagnosed it .. Then you ARE under nourished. No denying it. If you were told you look that way, that is why.
As concerning as that is .. Fan of food or not, I am sure you are an intelligent person who knows what that does to the body and how it looks, and more importantly how unhealthy that is for brain function.
I encourage you to talk to your doctor about this condition a little deeper before you do so much damage that you will pay consequences for the rest of your life.