In my longer runs I’ll consume a gel at the first hour mark and then ever 30 minutes. This can be for up to 4 to 5 hours. Gels allow me to consume a controlled amount of carbs without consuming too many calories. I’m not sure about cycling, but in ultra running gi issues are one of the main reasons for dnf’s. The funny part is on runs longer than 6 hours, I supplement gels with mashed potatoe burritos.