The gut is trainable — just like muscles. Most cyclists can only absorb 40-50g/hr of carbohydrate without GI distress when untrained. With 2-4 weeks of progressive practice (starting at 40g/hr and adding 10g/hr per week), most riders can tolerate 80-90g/hr using a 2:1 glucose:fructose ratio. This is the protocol used by World Tour teams. Train your gut in training, not on race day.