Yeah, it's not just the food, but how much you eat. Did you see the portions that Spurlock was consuming in his movie? Double-fisting SuperSized drinks along with shakes! Who in their right mind can even eat that much? Unless you're training for eating contests or somethin'. For a while there when I was working full time in office and going to summer-school and didn't have much time for lunch, I'd grab a quick medium chocolate shake at Mickey's and run off again. I actually lost about 20-lbs that summer!

I can also sit around the house, never exercise and eat a tonne of the leannest choicest beef you can get, the most gourmet holistic naturally grown organic foods and I can also gain weight!

As John implied, weight is a poor indicator of health anyway. Total body-fat % would be a better indicator combined with LDH/HDL ratio, blood-pressure and resting heart-rate. If you improve those indicators, the weight-loss is pretty much automatic and guaranteed.