It's not always a good idea to emulate the diets of elite athletes, many of whom believe that (as a teammate of Olympic marathon champ Frank Shorter once put it) "if the furnace is hot enough, anything will burn, even Big Macs."
But sometimes they get it right.
For the past few years, top endurance athletes have been guzzling beet juice before their races to load up on nitrate, which helps muscles use oxygen more efficiently. We usually think of nitrate as a nutritional villain in foods like hot dogs and bacon, but a growing body of research suggests that it actually plays a crucial role in cardiovascular health, and may even explain the long-standing mystery of why leafy green vegetables are so good for us – as long as you don't use too much mouthwash.
The most recent study, published last month in the journal Hypertension, showed that simply drinking a cup of nitrate-rich beet juice lowered high blood pressure by more than 10 mmHg within a few hours, with effects persisting a day later. In comparison, severely restricting your salt intake will reduce your blood pressure by about 5 mmHg on average.
The beneficial effects are actually produced by nitric oxide, which has well-known cardiovascular benefits; it was only in 2008 that researchers realized that humans could convert nitrate from food into nitric oxide in significant quantities. The key: friendly bacteria that live in the mouth, which convert nitrate in saliva to nitrite, a related ion with one fewer oxygen atom that is then converted elsewhere in the body to nitric oxide.
"Nitric oxide does many good things," explains Dr. Amrita Ahluwalia of the William Harvey Research Institute in London, the lead author of the new study. "It opens up your blood vessels to lower blood pressure; it stops platelets from being sticky; and it prevents the blockages that lead to stroke and heart attack from forming."
Several studies from groups in Sweden and Britain have now established the acute effect of nitrate on blood pressure, and longer trials are now under way to see whether the benefits persist with a chronic high-nitrate diet – an idea that would have sounded foolish even just a few years ago, given long-standing concerns about the links between nitrate in cured meats and cancer.
Nitrate and nitrite are added to cured meats as a preservative; it's thought that at high heat they can combine with another group of chemicals found in cured meats, amines, to produce carcinogenic nitrosamines.
"This fear emerged in the 1960s and 70s, but it hasn't been substantiated in later studies," notes Dr. Eddie Weitzberg, a medical researcher at the Karolinska Institutet in Sweden who has conducted some of the key studies on dietary nitrate.
Either way, that potential risk doesn't apply to the nitrate found in vegetables, which don't contain amines. Leafy green vegetables like spinach and beet greens, in particular, naturally have so much nitrate that you could easily exceed the outdated recommended maximum for nitrate simply by following nutrition guidelines on vegetable intake, Weitzberg says.
There is one potential barrier to the effectiveness of a nitrate-rich diet: mouthwash. Rinsing with a mouthwash containing a powerful antibacterial agent like chlorhexidine wipes out the bacteria that convert nitrate to nitrite for 24 to 48 hours. Other mouthwashes don't have quite as dramatic an effect – "One might say it's lucky that products like Listerine are not so potent," Weitzberg says – but it's still unclear whether using mouthwash on a regular basis might interfere with the nitrate benefits of
Andy Jones, a researcher at Britain's University of Exeter who has spearheaded research into the endurance benefits of nitrate for athletes (his Twitter handle is @AndyBeetroot), has a study under way now comparing the effects of high- and low-nitrate diets with and without antibacterial mouthwash.
"No matter how good the diet," he says, "it may be in vain if we kill off our oral bacteria."
The other question is how best to get your nitrates. While Weitzberg has used isolated nitrate salts in studies, he and the other researchers strongly suggest that it's better to get your nitrate from vegetables. This makes it more or less impossible to get too much, and also avoids confusion with nitrite, which can be lethal at the wrong dose.
Given the poor results of previous attempts at extracting the "magic" from healthy foods – antioxidants, for example – this seems like excellent advice. By sticking with whole foods, you'll be sure to get the benefits you're looking for, and will undoubtedly consume many other helpful compounds, too.
So yes, in the end, this is yet another admonishment that you should eat more vegetables. But now you have an extra incentive: It's what all the Olympians are doing.
Nitrate-rich vegetables lower your blood pressure and may also have other cardiovascular benefits. Your best bet is leafy greens (or the roots of plants with leafy greens, like beets). Some top sources (bear in mind that a serving of beets weighs much more than a serving of arugula):
Arugula: 4,677 mg/kg
Rhubarb: 2,943 mg/kg
Beet (root): 1,379 mg/kg
Celery: 1,103 mg/kg
Swiss chard: 1,690 mg/kg
Alex Hutchinson blogs about exercise research at sweatscience.runnersworld.com. His latest book is Which Comes First, Cardio or Weights?