Comment by noelwelsh

Your muscles need energy to work. You have a variety of energy stores in your body, which range from small amounts of quickly available energy (ATP) to large amounts of slowly available energy (fat). Most relevant to this discussion is glycogen, which is is a carbohydrate. You have about 500g in your body, which is about 2000kcal. It is more readily accessible than fat, and 2000kcal is enough for an hour, or maybe two, of high intensity exercise.

These gels and drinks are trying to replenish glycogen stores. The idea is to keep the runner using glycogen for the entire race, as it provides more energy per unit time than fat metabolism.

In your hikes your energy demands probably aren't exceeding the rate that your fat metabolism can provide.