Carbohydrate is what is needed - period. Now there is some discussion that for REALLY long events, there MAY be a need for Fat/Protein in the mix. When they say really long, an IM may be at the threshold of being realky long.
The things that need to be kept in mind are as follows:
1) As intensity increases the need for carbohydrate as fuel at the muscular level increases
2) The body has stores of about 2 hours of Carbohydrates - hence the "wall" at 20 miles or 2 hours of a marathon if nothing taken in.
3)As intensity increases gastric(stomach) absorbtion and functionality decreases
4) As more complicated substrates( fats/proteins) are added to what ever is taken in gastric functionaity is further comprimised.
In summary - If training racing longer than 2 hours carbohydrates need to be taken in and the process needs to be simple as possible due to the increased demands put on the stamach. Not sure why so many people have these incredibly complex and complicated routines that from what I have seen can lead to more problems, then the simple task of getting carbohydrates to the muscles as quickly and easily as possible.
Steve Fleck @stevefleck | Blog