I think carbohydrates and sugars are the worst things for you. The way I understand it is that refined sugar and carbs are processed by the liver and turned into fat cells. Fat is not. If you're going to eat carbs and sugar, do so just before an activity and your body will use the fuel. If not, it will store the fuel as fat cells and you'll never get rid of them. I'm no nutritionists but that's what I've read.