1 Doughnuts
I can count the number of doughnuts I've had on the fingers of one hand since I read Joseph Mercola's advice on them several years ago. First off, doughnuts are made entirely from refined and processed flour and sugar. Wheat is not the most nutrient dense of foods to begin with (nutrition data), but once it is refined to white flour it has hardly any goodness left in it(nutrition data). Sugar even more so. The fact is the more nutrient dense your food the longer you live. I went to dominica a volcanic island with very high nutrient dense foods where many locals live over 100 years despite having low medical budgets.
Apart from the low micronutrition, the donuts do pack in a lot of energy calories. They also have transfats due to the fact they're deep fried. When unsaturated fats are heated up they warp and bend. This makes them very foreign to our bodies and transfats are now acknowledged as a major contributer to clogged up arteries and heart attacks.

Gosh, all those problems with donuts has taken it out of me, I'll continue with the rest of the top five at a later date.