Well, I'll agree that 300 pounds is excessive, I'd say that some people are overly hysterical and judgemental about the issue.
I'm five foot nine and two hundred and twenty pounds - and I work out pretty much every day and have for a while. Admittedly, I don't eat as well as I ought to, but still - people have radically different body types.
Indeed, when it comes to clothes, I have a huge problem with shirts in that I have extremely broad shoulders and a thick neck, which means that I end up with shirts which either barely fit around the neck, or hang off my sides like a dress. It's a huge pain in the ass sometimes.
The one interesting thing is that I'm Canadian and, in Canada, I tend to be heavier than the average. When I cross the border into the United States, I tend to find that I'm far closer to average.
Not that I care (some Canadians wear it as a mark of superiority). After all, American weight is a mark of prosperity and, in general, fat people - like smokers - are probably saving the public health system money over the long run, if we account fairly.