I am extremely underweight. I'm a boy, age 14, yet weigh only 75 pounds. My BMI is a measly 14.6. However, I must have the most insanely fast metabolism ever. I generally eat MacDonalds once every 2 days or so. Other than that, here's pretty much a list of what I ate today-1 bag of Jack Links Beef Jerky, half a bag of Funyuns, 2 grilled cheeses, 1 pizza puff, 1 Turkey and Ham sandwich, and one Medium Dominoes Pizza. I drank 3 bottles of water and a 2 liter Sprite. I am also in no way puking myself. How am not fat. How?