Why Energy Drinks and Exercise Don’t Mix

image of energy drink contained in metal can with mysterious twister element, purple background

Do you sip a cup of coffee or two before a workout? What about an energy drink? Studies show that caffeine improves exercise performance for moderate-intensity, endurance exercise. Whether caffeine is effective for short periods of anaerobic exercise is less clear. During sub-maximal, endurance exercise, drinking as little as 2 cups of coffee improves performance., meaning you can go further without fatiguing after consuming caffeine than you can after drinking a non-caffeinated beverage.

Based on these findings, you might assume that energy drinks are a good choice. They contain caffeine and they have the word “energy” in their name. So, is sipping a can or two of an energy drink a good alternative to coffee?  Let’s compare the two and see whether energy drinks are a suitable replacement for coffee.

What’s in an Energy Drink?

The average 16-ounce energy drink has around 140 milligrams of caffeine. An 8-ounce cup of brewed coffee has about 95 milligrams of caffeine, so ounce-for-ounce the average cup of coffee has more caffeine than the average energy drink, although the caffeine content of energy drinks and coffee may vary, sometimes widely.

Energy drinks also contain other stimulants that coffee doesn’t have. One, in particular, called guarana increases energy and alertness. So, despite containing less caffeine per ounce on average, energy drinks may be more activating than coffee and other caffeinated beverages due to the other ingredients manufacturers add to these beverages. However, many energy drinks also contain taurine, an amino acid, found naturally in meat, fish, and dairy products. Many people mistakenly believe that taurine is a stimulant. In fact, it’s the opposite. Taurine mildly depresses central nervous system function. So, taurine may cancel out some of the energizing effects of the caffeine and guarana in energy drinks.

Some energy drink manufacturers also add B-vitamins to their drinks, based on the fact that B-vitamins support energy metabolism. Popular energy drinks may also contain herbal additives, like ginseng, that purportedly increase mental focus. In addition, L-carnitine is a common ingredient in energy drinks, based on the idea that it supports fat metabolism. Of course, many energy drinks also contain sugar, sometimes in large quantities.

Energy Drinks and Exercise

If energy drinks contain caffeine and we know caffeine boosts exercise performance, why not just sip an energy drink if you don’t like the taste of coffee? Unfortunately, they can have a negative impact on heart and blood vessel function. In fact, a 2016 study linked energy drinks with a short-term increase in the load placed on the heart. This load forces the heart to work harder. The researchers believe the combination of caffeine and sugar may be responsible for some of this effect but also point out that the taurine in energy drinks may be a factor as well. Another study found that they reduce blood flow to the brain and can cause a transient rise in blood pressure.

In addition, there are case reports of people experiencing heart irregularities, including cardiac arrest, after drinking large quantities of energy drinks. One theory is that energy drinks cause a coronary artery, a vessel that delivers blood to the heart, to temporarily narrow or spasm, thereby reducing oxygen delivery to the heart. Plus, research shows energy drinks increase the force with which the heart beats, thereby increasing the heart’s oxygen requirements.

But, are we likely to experience ill effects when we drink energy drinks and exercise? In a small, randomized, controlled study, one of the most reliable types of studies, a popular energy drink was linked with increases in blood pressure and stress hormones called catecholamines in young, healthy adults. Combined with the stress of exercise, this could be enough to cause adverse effects on heart function in some individuals, especially individuals who have undiagnosed heart disease.

Some People Metabolize Caffeine Slowly

To add to the concern, up to 25% of the population has a variant of the enzyme that breaks down caffeine. In these individuals, caffeine stays in the body longer. Studies show that slow caffeine metabolizers are more prone toward heart problems related to caffeine intake than fast metabolizers. In fact, a study in Journal of the American Medical Association found that subjects who metabolized caffeine slowly were at 36% higher risk of a heart attack or other serious cardiac event when they drank more than two cups of coffee daily. If they drank more than four cups daily, their risk rose to 64%.

Like coffee, energy drinks contain caffeine. So, a slow caffeine metabolizer should have a similar risk when drinking energy drinks. Plus, energy drinks contain additional stimulants, like guarana, that could increase the odds of an adverse effect even more. The only way to find out whether you’re a slow metabolizer is to get genetically tested.

The Bottom Line

Energy drinks have unpredictable amounts of caffeine. Plus, they contain other stimulating ingredients, like guarana, that can have an additive effect with the caffeine. Combine this with intense exercise, a rise in body temperature, and dehydration, it could have unpredictable effects on heart function.  In fact, a number of deaths related to energy drinks, some occurring during exercise, are under investigation.

If you’re trying to boost your performance during endurance exercise, it’s best to stick to coffee. Energy drinks contain additional stimulants that have an unpredictable effect on sports performance and may force your heart to work harder. If you know you’re a slow caffeine metabolizer, it’s safest to limit your caffeine to one cup of coffee daily, or two at most, due to the potential for it to stay in your system longer. Energy drinks have the added drawback of being high in sugar. Plus, the carbonation can cause digestive upset.



Mayo Clinic. “Nutrition and healthy eating”
Phys Sportsmed. 2010 Apr;38(1):107-17. doi: 10.3810/psm.2010.04.1768.
Adv Nutr. 2016 Sep 15;7(5):950-60.
Psychopharmacology (Berl). 2010 Aug; 211(3): 245–257.
Astorino T.A. et al. (2009), J. Efficacy of Acute Caffeine Ingestion for short-term high-intensity exercise performance: A Systematic Review.
Med J Aust. 2009 Jan 5;190(1):41-3.
Journal of Amino Acids. Volume 2013, Article ID 646703, 7 pages. http://dx.doi.org/10.1155/2013/646703
JAMA Research Letter. “A Randomized Trial of Cardiovascular Responses to Energy Drink Consumption in Healthy Adults”
JAMA. 2006;295(10):1135-1141. doi:10.1001/jama.295.10.1135
Shape.com. “Are Energy Drinks Safe? What You Need to Know About the Monster Energy Drink Death Investigation”


Related Articles:

Why Caffeine after a Workout Has Potential Benefits

How Much Can Caffeine Improve Exercise Performance? It Depends on This

Can Drinking Coffee Before a Workout Make Exercise More Enjoyable?

Should You Drink Coffee Before a Workout & If So, When?

Can Drinking Coffee Boost Your Metabolism?

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