How fat am I?

So I was watching the London marathon coverage ten days ago, which was full of all the usual inspiring stories, including a bloke who was 23 stones a year ago, and had lost more than half his body weight or something crazy to take part in the run. (One of the reasons why I am now doing the same thing).
But it made me think that these days, you've got be 20 stone plus before anybody takes you seriously as a fatty.
I mean, at 18 stone I thought I was pretty fat, and indeed I am, but next to that guy, and many people I see around Bristol, I'm a mere slip of a lad.
The whole thing has shifted up several gears.
But I can't imagine how I can fit any more lard into my body. I had a heart operation in 2007 which has left me with a rather impressive scar down the middle of my chest where they had to saw through my sternum. Ouch. Anyway, there are times when I worry it's going to split like a zip bursting on a pair trousers.
So how anybody could get up to the likes of 50 stone is beyond me. Although in a weird way I am impressed by anybody who can eat enough to get that big. Judging by my food diary I reckon I won't be far off. It does look like a lot when you write it down.
It's weird but when I told a former colleague I was aiming to lose eight stone, she said that was how much she weighed. That means I can shed the weight of a whole person, a full grown adult, and still have enough to go round.
And so it has begun. I went for my first run on Tuesday, and considering the driving wind and rain, I felt very brave and manly. I ran about a mile, very slowly and stopped a couple of times to walk. But I kept going when I thought I might give up completely, so I'm pleased with that start. Only 25 miles to go.