McDoubles were popular with skinny guys who had a hard time putting on weight. One would stuff their faces with calories and hit the weights in order to do get bigger and it would be very hard if a guy didn't get in enough calories. So that's why a calorie dense item like a McDouble would help. However, that's changed with McDonald's increasing prices such that you aren't getting protein bang for your buck. Now, as one poster had already stated, you get a better deal (monetary and nutritional) with chicken, milk, lentils, beans, whole wheat pasta and eggs.