Most of the time, bloggers claim that they generate news. They're wrong. They might hype stories up, but their sources are usually the standard media, especially with big sources. How do I know this? Because I co-wrote an academic paper on the subject. Read it here.
This story's different. It's untrue, as far as we can tell. As this Guardian story explains it, a blogger heard from a civil servant that Brown isn't allowed to eat cheese, salami, various other foods and red wine. He decided that this was stuff he was banned from consuming when he was on anti-depressants in the 1980s. Cue 'Brown depressed story'. Then a bigger site picked it up, as did all the conservative sites out to get Brown. Once enough sites were howling about it, it leaked into the mainstream media.
This is obviously a failure of journalistic standards, but also a beautiful demonstration of the shortcomings of blogging: a weird opinion is amplified by partisan interests during a period in which an individual is already fair game. Instead of ascertaining facts, opinion and speculation are accepted and even encouraged because it's arresting - it's the Fox News approach.
My two cents: if Brown is banned from eating these things, it's because he's in his late 50s and prone to getting a bit porky. I shouldn't be eating these things either.