I think it's just one of those things that depends on how you carry your weight. Some people carry excess weight in their feet - and it doesn't take a lot to go up 1/2 size or from a medium to a wide. But other people have small feet even with extra weight, and they aren't likely to see a big difference.

I'm not positive which category I fall into though! lol! I currently wear either an 8 or 8.5 M. When I was younger, it was 7.5 to 8 but I'm not sure whether that change was from weight or age. I didn't change sizes during my pregnancy, though.

I haven't noticed a darn bit of change, even after losing 60-70 pounds-ish. Of course, I wear a loose size 10, and my sister--who's never had anything even close to a weight problem--wears a 9 1/2, And my brother wears, like, a 14 or something men's. So I suspect that they're going to stay big. Meh. The size of my feet's never bothered me, and my ankles are skinny enough now to make my tie-on moccasins look good, so I'm happy.

at 170 lbs, I wore a size 8, and now at 135ish, I wear a 7!