The dude who eats two Big Macs and a Sprite everyday is still alive.
In addition to the point that Spurlock outright lied about his alcoholism in the film (some of his symptoms were compared to an alcoholic suffering withdrawal...because that's exactly what it was!) he was also intentionally overeating and engaging in abnormally unhealthy behavior. Some have noted at some points he had to be consuming about 4000 calories a day. That's basically an Olympic athlete-level diet except Spurlock was clearly not working out at the level of an Olympic athlete. He was actually limiting his steps and physical activity and continuing to eat when he was full.
Some people replicating his all McDonald's diet experiment actually reported
losing weight when it was paired with a solid level of physical activity and portion control. It goes without saying eating only McDonald's is not healthy or a good idea, but the movie didn't accurately portrwy it at all.