["I eat a lot but don't get fat.", 'Do you have a fast metabolism then? I wish I had that!', "Maybe so. Although I don't get fat, it doens't mean I'm healthy. I'm just glad I don't have to worry about weight."]
Make sure you have routine physicals so that you can get anything else that might need to be adjusted fixed, etc.. but you are right, at least you don't have to worry about weight.
I eat a lot but don't get fat.