"Should I eat gels during a marathon?" We get asked this question frequently. The short answer is: probably!
If you've ever hit the wall in a marathon, it's most often due to running out of carb energy. For the typical marathoner, this happens somewhere between mile 18-22. It's caused by depletion of glycogen reserves, stored in the liver and muscles. Hitting the wall makes it very difficult to keep running and most runners slow to a dizzy walk.