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 . Additionally, make sure you drink water with a gel to stay properly hydrated.