I have been very thin my whole life, well, it started when I was about 10. The doctor told me that I have a fast metabolism, which means my body breaks down food quickly and only stores a very little amount as fat.
So basically, if I were to intake a lot of calories, I still would not gain weight. People simply tell me "Eat McDonald's everyday"!. trust me, I've tried that but with no luck.
Is there ANY possible way to gain weight by slowing down my metabolism? What certain foods should I be eating? Proteins, carbs, calories?