Although it’s entertaining, Super Size Me is mainly propaganda. Like LuLu said, Spurlock didn’t just eat McDonald’s, he ate ridiculous quantities of it. There were plenty of people who did their own studies losing weight by eating at McDonalds, just by counting calories–not to mention the guy who’s eaten literally nothing but Big Macs and Cokes most of his adult life, while staying thin and healthy. It doesn’t matter much what you eat if you eat a sensible quantity.
If you want examples of people who can binge on tons of calories, while staying fit, look at endurance athletes. Michael Phelps is the example everybody knows, but any serious distance runner has to eat like a garbage truck. I read a story about an ultra marathoner who had pizza delivered to him on his running route, just to stay fueled and avoid unwanted weight loss.
If you want to eat lots of calories, burn lots of calories. It’s the way everyone lived–hunting, gathering, or working in the fields with heavy tools–for most of human history.