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Coffee contains a wide range of bioactive compounds that influence human health. Evidence suggests that coffee consumption reduces the risk of cardiovascular disease-related deaths and certain types of cancer. Findings from a new study suggest that caffeine in coffee improves fat metabolism when consumed prior to exercise.

Caffeine is an alkaloid compound with potent stimulatory effects. Evidence indicates it improves performance in both endurance and resistance exercise. Some of these effects may be due to caffeine’s capacity to decrease the perception of effort and increase the neural actions on muscle fibers.

The triple-blind, placebo-controlled, crossover trial involved 15 healthy men (average age, 32 years) who were endurance trained but not regular consumers of caffeine. The men cycled on a stationary bike while slightly increasing the resistance every minute until they reached exhaustion. The test was performed four times, either in the morning (8 a.m.) or afternoon (5 p.m.), with each test separated by seven days. Thirty minutes prior to exercising, the men ingested either anhydrous caffeine powder from green coffee beans (3 milligrams per kilogram of bodyweight) or a placebo. The authors of the study monitored the men’s heart rate, maximal fat oxidation (and the exercise intensity at which it occurs), and respiratory function (VO2 max) during the exercise test.

They found that maximal fat oxidation and the intensity at which it occurs exhibited a diurnal pattern, with higher values seen when the men exercised in the afternoon rather than in the morning. Caffeine potentiated the diurnal effect, increasing the men’s average maximum fat oxidation by nearly 11 percent in the morning and 29 percent in the afternoon. Caffeine also increased the exercise intensity at which the fat oxidation occurred by 11 percent in the morning and by 13 percent in the afternoon.

These findings suggest that caffeine improves fat oxidation in endurance athletes and these effects are influenced by a diurnal rhythm. Consuming caffeine in the morning maximized fat oxidation to a degree similar to that seen without caffeine in the afternoon. It is important to note that while caffeine intake may improve fat oxidation, intake late in the day can impair sleep, potentially negating some of the beneficial effects of exercise. Learn more about the effects of caffeine on sleep in this clip featuring sleep expert Dr. Matthew Walker.

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