Aaron Reddwrote a review of GU Energy Gel - 8-Pack on January 27, 2020
Familiarity: I've used it several times
Endurance athletes can be at it for hours on end, and much of the time the body doesn't have the sugars to last longer than about 1.5-2 hours. Gu gels help provide sugar for your brain and keep you awake. I have definitely felt my vision get fuzzier and my reaction time get slower when I go to long on a run without one.