If you’re a runner or cyclist who participates in races, you’d, no doubt, like to maximize your exercise endurance. Over the years, studies have looked at a variety of foods that appear to modestly boost exercise endurance. One of these is beetroot juice, a beverage that increases blood flow to contracting muscles. But, beetroot juice has a little competition from an unlikely source – dark chocolate.
Who doesn’t love chocolate? Dark chocolate is possibly the healthiest food that also doubles as a decadent dessert. In fact, dark chocolate is often touted for its heart-healthy benefits. Plus, there’s evidence that dark chocolate is a heart-healthy treat. Now, a small study shows that munching on dark chocolate may actually boost exercise endurance. Sound too good to be true?
What the Study Showed
To explore the potential endurance benefits of chocolate, researchers at Kingston University enlisted nine amateur cyclists. First, they asked the cyclists to complete a fitness test to measure their baseline level of aerobic fitness. Then, they divided the subjects into two groups. One group of cyclists replaced one of their daily snacks with four squares of dark chocolate. The dark chocolate squares were tested and confirmed to be high in flavanols. The other group ate white chocolate instead. Unlike dark chocolate, white chocolate doesn’t contain flavanols at all. In total, the participants ate 40 grams, around 1.4 ounces, of chocolate per day in place of another snack.
Afterward, the cyclists took part in cycling fitness tests. After a week on one routine, the cyclists switched the chocolate type the participants consumed. The dark chocolate eaters consumed white chocolate and vice versa and the tests were repeated. After tabulating the results, the researchers found that the cyclists required less oxygen during a cycling workout when they ate dark chocolate as opposed to white chocolate, leading to greater endurance. They were also able to cover more distance during time trials. Other studies looking at beetroot juice have shown similar benefits.
Dark Chocolate and Endurance
Why might dark chocolate improve exercise endurance? The most likely compounds responsible for this potential benefit are the flavanols in dark chocolate, particularly one called epicatechin. When you eat a piece of dark chocolate rich in epicatechin, it stimulates the walls of arteries to produce a gaseous chemical called nitric oxide. Nitric oxide, in turn, helps open up the blood vessels to allow better oxygen delivery. Better oxygen delivery means that muscles that are contracting so hard during exercise get oxygen faster and can sustain exercise longer. This adds up to better exercise endurance and that’s desirable if you play sports, run, or cycle.
In addition, the flavanols in dark chocolate have heart-health benefits. The increased oxygen delivery that benefits your muscles also boosts blood flow to the most important muscle in your body, your heart. Ingredients in dark chocolate also make platelets in your bloodstream less sticky and this helps lower the risk of a blood clot forming. When a blood clot forms in an artery that supplies oxygen to your heart, it can lead to a heart attack. If it’s a blood vessel that supplies blood and oxygen to your brain, the result is a stroke. So, eating moderate amounts of dark chocolate may lower the risk of heart attacks and stroke. Plus, the types of fat in dark chocolate don’t seem to raise cholesterol or adversely affect blood lipids.
In fact, a study that followed 21,000 middle-aged and older adults in England for 11 years found that those who ate the most chocolate had a lower mortality rate than those who rarely consumed this delicious treat. Some of the adults in the study ate a fair amount, the equivalent of two dark chocolate bars, but other research suggests you can get benefits by eating only 2 ounces daily.
Not All Dark Chocolate is Created Equal
You might think you can grab any dark chocolate at the supermarket and reap the benefits. Not necessarily. The flavanols in dark chocolate are rather bitter. To make a dark chocolate bar taste sweeter, some manufacturers use alkali, a process called Dutch processing. Unfortunately, this also destroys most of the beneficial flavanols in chocolate. When you choose dark chocolate, make sure it wasn’t Dutch processed or exposed to alkali. It should say so on the label. Also, look for a brand with a cacao content of at least 70% and a bar that’s low in sugar. Even better, research the company you buy your dark chocolate from as even some bars that have a cacao content of 70% or higher fall short when independently tested. For example, some listed as 85% cacao contained as little as 56% cacao.
Another caveat, be aware that when Consumer Lab independently tested a variety of dark chocolate bars, including organic ones, some were contaminated with the heavy metal cadmium, a particularly dangerous metal that your body can’t eliminate. In fact, some had concerningly high levels. Know what you’re buying, especially if you eat dark chocolate every day. Cocoa powders and cocoa nibs also may contain heavy metals, like cadmium, particularly cocoa powder.
The Bottom Line
Dark chocolate may help modestly boost exercise endurance, although more research is needed. Still, the evidence that dark chocolate is healthy for the heart and blood vessels is well established. However, do a little research before grabbing a dark chocolate bar to avoid the downsides such as low levels of flavanols, too much added sugar, and contamination with heavy metals. You might find dark chocolate with a high percentage of cacao a little bitter at first, especially if you’re accustomed to milk chocolate, but eat it regularly and you’ll soon find sugary, milk chocolate tastes TOO sweet and dark chocolate tastes just right. So, enjoy dark chocolate in moderation. It’s one of the best-tasting “medicine” around!
References:
Science Daily. “Eating Dark Chocolate as a Daily Snack Could Help Boost Athletic Performance”
Nutr Rev. 2008 Nov;66(11):630-41. doi: 10.1111/j.1753-4887.2008.00114.x.
Consumer Lab. “Product Review: Dark Chocolate, Cocoa Powder, Nibs, Extracts & Supplements — Sources of Flavanols”
Harvard Health Publishing. “Sweet dreams: eating chocolate prevents heart disease”
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