I'm not a particularly big fan of doughnuts but I do tend to eat one or two large bagels (which don't have nearly as much sugar content as doughnuts but do tend to get lumped into that whole "carbs are evil" thing) before going on a long run or bike ride. I also eat more fatty meats than average but that goes along with doing heavy weight training at least 3 times a week.
There are many foods that looked at out of context aren't particularly "healthy" if considered against an average modern sedentary lifestyle but which are sources of either quick energy or useful protein which can be beneficial for weight management and overall health if properly utilized.
All of this is why talking about diet without also talking about exercise is useless.
My completely non-scientific belief is that while over-consumption of sugar isn't a great thing, the primary thing making us fat is that we've switched to a massively sedentary lifestyle on average. We aren't toiling in the factory or on the farm or walking door to door selling vacuums, and mostly that's a good thing because those jobs aren't particularly interesting for many of us, but at the same time our bodies aren't really evolved for sitting down 8-16 hours a day.