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Nutrition FAQ: Caffeine in Sports Gels, Caution on Diuretic Effect
UPDATE: this might be true in a lab, but I reject its credibility during double centuries as false, where I would consume 6 to 12 liters of fluid over 11 to 16 hours containing 650 to 1200mg of caffeine.
Energy gels like Gu have 20mg caffeine per packet (most flavors), or even 40mg for some flavors (Jet Blackberry), and 0mg for others.
Too much caffeine for 3+ hour endurance events?
If an athlete consumes three energy gels per hour, each containing 20mg caffeine, the diuretic effects of caffeine could in theory begin to be a problem after about 3 hours:
3 packets per hour X 20mg/packet X 3 hours = 9 X 20 = 180mg caffeine
For energy gels with 40mg of caffeine per packet, such as Gu Jet Blackberry, the caffeine adds up quickly.
Mitigating by mixing non-caffeinated energy gels
A mitigation strategy could be to intermix other non-caffeinated flavor, thus restricting the caffeine intake to 40mg per hour, which would allow 4 hours of consumption without diuretic issue.
Elimination of caffeine over time
Since the body eliminates caffeine over time, some steady-state consumption is possible. How fast the body can eliminate caffeine under endurance events is unclear, and affected by overall exertion and hydration.