I've also worked in several large tech companies before and most of the workers aren't fat. In fact, at Google, we're given healthy meals and encouraged to exercise (there's physical activities available in the office like ping pong tables, gym, etc.). There has never been a stereotype among CS programmers that we're fat. It's usually that we're awkward, introverted, shy and condescending towards people who can't use logic.

But whenever I hear about the fat nerd stereotype, it's usually about gamer nerds. They even made a whole South Park episode about it. And if you check the post history of the person who I'm responding to, you'll see that he plays video games enough to post them on YouTube. So, being fat might have more to do with excessive gaming rather than going to work to sit all day in front of a computer (which is something non-computer nerds do too if they work in an office setting). That's why I'm saying that maybe he got his stereotypes mixed up.