We have a fast food restaurant called Mighty Taco by us. It's sorta like Taco Bell, but a lot fattier. There is more fat in Mighty than in McDonald's. I got their Mighty Pack (like a family pack, 6 medium size tacos) today, and ate the entire thing after our practice and meet today. I won't gain anything. Given, I won't be able to do that in 20 or even 10 years, but still.
Now most people don't do that. As long as you eat like a normal person (do you really need that dessert?) and work out regularly you don't have to worry about your weight too much.