Nitrate
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Nitrate

Perhaps Popeye should dole out nutrition advice. Turns out the cartoon sailor man's go-to bicep bulker – the trusty can of spinach – really does strengthen muscles. Swedish scientists just determined that nitrate, a compound abundant in spinach and other leafy vegetables, can build and tone muscle and in turn boost athletic performance.

In a study published in The Journal of Physiology, researchers added nitrate directly to one group of mice's drinking water and not to the other's. After only one week, the nitrate-fed mice had sprouted significantly stronger muscles than the non-nitrate group. Interestingly, however, only the fast-twitch muscles – those used for high-intensity workouts – were affected, while no change occurred in the slow-twitch muscles associated with moderate exercise.

How this all works isn't as simple as spinach directly beefing up brawn (sorry, Popeye). "Rather than 'building muscle,' per se, like we typically associate with strength training, dietary nitrate was shown to improve muscle contraction force," says Ted Weiss, a professor of nutrition and dietetics at Saint Louis University who has also published research on nitrate's effect on athletic performance. He explains that nitrate triggers an increase in two key proteins found naturally in muscle that regulate the movement of calcium between different regions of the cells. This calcium shuffle plays a vital role in muscle contraction. "Because nitrate increases the number of these proteins, muscle can contract with more vigor," he says. In short, the more calcium delivered, the stronger the contractions, meaning faster running, more efficient pedaling, and quicker response times on the tennis court.

And here's the best part: The amount of nitrate needed to strengthen muscle in mice translates to a totally attainable human-size helping of spinach or other vegetables, such as beets, bok choy, and carrots. "Since nitrate is present in numerous veggies, simply shooting for the USDA-recommended vegetable intake of 3 cups per day will supply enough," Weiss says. "But if you want to look to one food specifically as a nitrate source, you can get your daily dose from 2 cups of sautéed spinach or two moderate-sized spinach salads. Or you can mix up a large smoothie made with beets, collard greens, or kale."

Weiss also notes that the mice study's short seven-day regimen suggests that nitrate can provide a fairly quick performance boost. In other words, put down the pre-10K pasta and pile on the produce instead. "Be sure to load up on vegetables a few days before a big athletic event," he says. "At the very least, go veggie heavy for your pre-race meal."