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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.
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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.