As I said, it's not gonna be chicken and broccoli, but I could easily have 800-1000kcal of any starchy side dish (say 250g of dry white rice/pasta) 3 times a day. Add meat, fruit, and a small treat here and there, and you're at 5000 without even touching fast food. Believe it or don't, I'm 6'5 and come from a family of fatasses, people marvel at how much I can put away wherever I go. Not saying it's that way for everyone, but you should still be able to get enough calories to grow from 3 square meals.