I eat fairly healthily, most of my main meals are fairly good in terms of fat, vitamins, calories etc... my downfall is my sweet tooth, and the deli down the road from my house, stacked with delicious cakes

which keeps me at just under 11st (I'm short at 5' 5'') despite running 40-50 mpw.
I don't feel bad for what I eat, I enjoy eating well, but I probably would do if I was not doing as much exercise. I'm actually thinking I might crack down on the sugar and try to lose a few pounds after my next marathon
Running is supposed to be great at eliminating cholesterol. If you find you can eat all that food without weight gain, and feel hungry all the time, then it could be you have a naturally fast metabolism. Or you could try eating protein instead of carbs or sugar when you are hungry; this makes you feel full for longer.