Training for a marathon? Look at you, superstar! If you've got a long road of long runs ahead of you, odds are, you're no stranger to loading up on good-for-you, pre-workout fuel foods. But there's an obvious choice you might be overlooking. And thanks to its crazy good endurance benefits, it's one you really just can't afford to skip out on any longer. Behold, the new pre-workout superfood: beets!

Long heralded for its work out boosting power, beet converts have been singing the food's praises for years. Many a fitness guru have suggested that drinking beetroot juice before a workout can boost performance, improve blood and oxygen flow to tired muscles, and increase endurance. Even doctors are on board with beets, and many studies have tested the potential ergogenic (read: performance enhancing) effects of beets in athletes. But what exactly does all that mean?

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Nutritionally speaking, beets have got it goin' on. Thanks to their high carb content and a heavy hit of dietary nitrates, beets possess serious performance potential. Here's the long and short of it: beets are rich in nitrates — including a particular type (Dietary Nitrates) known for morphing into nitric oxide inside the body. When this happens, the switch is said to relax blood vessels and encourage more productive blood flow to working muscles. And when you're crushing it on the stairmaster, this is the exact type of bodily voodoo you want to see happening in your system.

I chatted with a doctor friend of mine to see if there was any truth to the theory, and although the logic follows, she also wondered how much of the effect was mental. As is often the case with any food said to offer specific and heightened health benefits (red wine that fights heart disease, blueberries that offer a hit of antioxidants), many doctors maintain that you'd have to eat quite a bit to see any real, ground-breaking results. But after consulting registered dietitian Heather Steele, it seems like the theory checks out. "Research definitely suggests that it's beneficial," she confirmed. "It has to do with the nitrates in the beets. Typically, [beet consumption] increases the VO2 max."

The VO2 maxessentially indicates endurance. When dietitians and cardiologists study VO2 max, they're looking at oxygen intake and output, and how long the subject can sustain exercise at a certain oxygen level. With the help of beets, subjects are able to exercise longer, and more efficiently.

But when it comes to activity-boosting beets, how much is enough? According to Steele, fresh beetroot juice is usually more effective than canned beets. "Canned beets don't seem to have the same nitrite content that a fresh beet would have," she explains. Though depending on your location, it might be challenging to find fresh beet juice. For best results, drink a cup of juice, or eat a cup of fresh beets about 30 minutes to an hour before working out.

You can also mix the superfood with other, complimentary pre-workout snacks. When you're about to do serious physical work, something with healthy carbs is usually a safe best, as they tend to offer a quick boost of energy right before you get to work. A snack packed with quick-digesting, healthy carbs -- like a beet, apple, celery, arugula, and almond milk smoothie -- might do the trick.

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Also, beets are delicious! Don't be fooled by their rough, dried-up, dirty-looking exterior; on the inside, beets are smooth, buttery, velvety, and perfect for munching with goat cheese, in salads, with veggies, or on their own. Even better: Their thick skin keeps them fresh in your refrigerator for up to two weeks, says Malone. And they're less sensitive to ethylene, which means they can stay near other vegetables without going bad.

PS- some lab studies have even shown that beets reduce or reverse certain types of tumor growth. If you're not yet on the beet bandwagon, time to get on board.

Just don't be alarmed if the, ahem, benefits pop up the next day; it's said that anywhere between 10-15% of adults experience beeturia after eating beets.

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