Caffeine: Exercise and Fat Oxidation
Monday morning. Need I say more. We wake up, drag our half-asleep bodies to the kitchen and, while fighting to keep our eyes open, make ourselves a nice warm cup of coffee. Only then, after the caffeinated liquid diminishes from our cup, do our eyes widen and our day begins. Whether you’re a strong believer in the power of a cup of coffee or have yet to surrender yourself to the magic of caffeine, the effects of caffeine on your body are worth considering.
Caffeine is alkaloid xanthine derivative found in coffee beans, tea leaves, cacao beans, and cola nuts. The recommended maximum intake of caffeine that is considered safe is 400 mg/day. This correlates to roughly 4 cups of coffee. An intake above this may result in adverse side effects that include: insomnia, nervousness and irritability, headache, a fast heartbeat, frequent urination, and an upset stomach. Individual sensitivity to caffeine may vary, so for those that have never consumed caffeine, it is recommended to start with a smaller dose to see how your body will react before increasing consumption. Furthermore, medications may interact with caffeine and a physician’s authorization is suggested before consumption.
Once ingested, caffeine is rapidly absorbed, taking only 15 minutes to kick in. Peak caffeine concentration can occur between 15 -120 minutes after initial consumption and effects may last up to 6 hours. The fast absorption rate by the body is due, in part, to the structure of caffeine itself. Caffeine has a similar structure to adenosine, an inhibitory neurotransmitter that promotes sleep and suppresses arousal when bound to a receptor. It seems quite ironic that the very molecule that promotes sleep has a similar structure to the molecule that stimulates the body. This similarity, though is key to caffeine’s function in masking sleepiness. As caffeine enters the blood brain barrier, it binds to adenosine receptors in the brain. By binding to these adenosine receptors, caffeine acts as a competitive inhibitor, blocking adenosine from binding and masking the need for sleep. This leads to the well-known alertness associated with caffeine consumption. Interestingly though, as the blood concentration of catecholamine’s (stress hormones such as adrenaline) rise, not only does our heart rate increase, but our concentration of lactate, glycerol, and free fatty acids does as well.
Why is this information important? Researchers believe that the multiple effects of caffeine may not only play a role in increasing alertness, but can also act as an ergogenic aid to exercise and increase fat oxidation at rest. At rest, the body relies more on fat oxidation due to the increased plasma free fatty acid concentration in the blood caused by caffeine consumption. The slight increase in fat oxidation elicited by caffeine consumption, should not be used as a substitute to exercise, rather it should be used as a supplement to it. Caffeine consumption has been shown to aid in increasing exercise the volume of endurance training. Caffeine ingested before exercise has been shown to reduce pain sensation and decrease the rated perceived exertion of training. Although consumption does not preserve glycogen fuel use, it aids in increasing exercise volume, therefore helping you last longer during workouts to burn extra calories.
The effect of performance improvement can be found even in lower doses of about 1.5–3.0 mg/kg of caffeine. To utilize the maximum benefits of caffeine consumption, ingestion should occur 1 hour prior to exercise. So, before your next workout, grab a cup of tea, ice cold latte, or shot of espresso, and smile to yourself knowing that with each sip (and each step on the treadmill) you can become a fat burning machine.
B.S. Biochemistry, Exercise Physiology
University of Miami