It’s helpful to fuel with gels during a half marathon. If you’re running for longer than 75-90 minutes, you need to fuel mid-run to replace used glycogen stores. Gels are an easy-to-digest glucose source that are rapidly absorbed into the bloodstream, and also frequently contain electrolytes to replace the ones lost in sweat.
During a half marathon, it’s recommended to consume about 30-60 g carbohydrate/hour after 60 minutes of running to replenish your body [ 1
1]. Additionally, make sure you drink water with a gel to stay properly hydrated.
Rosenbloom, Christine PhD, RD, CSSD Food and Fluid Guidelines Before, During, and After Exercise, Nutrition Today: March/April 2012 - Volume 47 - Issue 2 - p 63-69, doi:10.1097/NT.0b013e31824c5cb8