> Or are people over fueling themselves?
Not possible, you burn calories way too fast! What is possible is to cause GI distress by consuming more than you can digest or consuming things that you are not used to or in ratio's or quantities that you are not used to. In yesterday's Tour de PPA I burned 2260 Calories in 2.5h. 800 - 900 Cal/h is about normal for racing for me. That is 200 - 225g of carbs per hour, which no one can digest. I am gut trained to handle 100g per hour, but the rest has to come from glycogen reserves and some minor fat oxidation that is at least somewhat possible at race pace.
Even at lower intensities that burns less calories and allows more fat oxidation to occur you will be going into your glycogen reserves from the start line. If you are not consuming carbs at your maximum possible rate you are limiting how hard you can go or how long you can go hard for.
