Frequently used in energy drinks, several varieties of guarana contain more caffeine then a coffee plant. (Some have shown levels up to 7 percent compared to coffee's 2 percent.) However, caffeine provides the body with perceived energy rather than actual energy. There's no proof that it actually benefits athletic performance. If you choose to use caffeine supplements like guarana, proceed with caution. Guarana's high levels of caffeine have reported side effects of jitteriness, increased heart rate and high anxiety levels.
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