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Caffeine causes the body to rely more on fat for fuel during a workout, rather than glucose," Aceto says. "But the caffeine effect is lessened when you eat a high-carbohydrate meal with it." Drink 1-2 cups of black coffee within two hours of working out, and emphasize healthy fats and protein if you're drinking it with a meal or snack. Skip the cream and sugar (which add unwanted calories and fat), and avoid drinking coffee at other times of the day; doing so can desensitize you to the fat-burning effects of caffeine.