“Research reveals new secret weapon for Le Tour,” read the press release headline, referring to the Tour de France. “Now there could be a new, completely legal and rather surprising weapon for riders aiming to shave vital seconds off their time – beetroot juice.”
Beetroot juice? Within 24 hours my local bike club forum was buzzing about the news. The research, published in Medicine & Science in Sports & Exercise (June 2011), is the latest in a series of studies on beetroot juice and exercise conducted by Dr. Andy Jones and crew at the University of Exeter (the University put out the press release).
The study found that men who consumed 0.5 liters (~17 ounces) of beetroot juice improved simulated 4 km and 16.1 km cycling time trial performance by 2.8 percent (11 seconds) and 2.7 percent (45 seconds), respectively, as compared to when they completed the rides after drinking a placebo. Power output increased while oxygen consumption was not changed, indicating cycling economy was improved. The participants drank the juice 2.5 hours before completing the rides, which were conducted on stationary bikes.
The nine competitive male cyclists (average age 21 years) who participated in this study were asked to avoid strenuous activity and refrain from caffeine and alcohol consumption prior to coming to the lab to ride. This is standard. But a subsequent step in the protocol is not standard:
“The subjects also abstained from using antibacterial mouthwash and chewing gum during the supplementation periods because these are known to eradicate the oral bacteria that are necessary for the conversion of nitrate to nitrite.”
Huh? It turns out beetroot juice is just the tip of the iceberg for an exciting and rather amazing area of research that also involves bacteria and spit. You’ll be hearing a lot more about this work and its implications for sports performance and health, so it’s worth a closer look.
Why beetroot juice?
Beetroot juice is chock full of inorganic nitrate. The nitrate (NO3-) gets converted to nitrite (NO2-), which is then converted to nitrogen oxides, such as nitric oxide (NO). Nitric oxide is a powerful signaling molecule that is thought to be responsible for the majority of the physiological benefits. [Nitrate is not the same as nitrite. See the section on risks below.]
Beetroot juice contains lots of nutrients, including antioxidants and polyphenols. To make sure the effects were due to nitrate, the researchers selectively removed just the nitrate from the juice. When participants were given this altered juice, they exhibited no improvements in cycling performance. (Thus the nitrate-depleted juice served as the perfect placebo for comparison against the regular juice.)
What’s with the mouthwash?
Humans lack the necessary enzyme to convert nitrate to nitrite and get the whole chain of events going. But it turns out there are bacteria that lounge in the back of our mouths that are pros at this. The nitrate we eat goes through a rather strange and wonderful journey:
- When we consume a source of nitrate, such as beetroot juice, the nitrate is rapidly absorbed by our small intestine. Nitrate levels subsequently rise in our blood stream and remain elevated for hours.
- Our salivary glands suck up about 25 percent of this circulating nitrate, concentrating it in our saliva (the balance of the nitrate ends up in our urine). Saliva levels of nitrate become 10-20 fold higher than blood levels, and can peak 30 minutes after ingesting nitrate.
- This salivary nitrate is then converted to nitrite by bacteria that hang out on the back of our tongues.
- When we swallow, our saliva, now full of nitrite, goes to our stomach, where the nitrite is converted to nitric oxide and other nitrogen oxides. Some of the nitrite also makes its way from our stomach back into our circulation.
If we use an antiseptic mouthwash, we stop the bacteria from working. If we spit (or don’t swallow), we deny our gut the nitrite-enriched saliva.
Yes, bacteria. Communities of bacteria reside in our mouths, our nasal passages, on our skin, in our gastrointestinal tract, in our urogenital tract, and in many other places where light doesn’t shine. For each single human cell we have, we have ten (10!) microbial cells.
We have a symbiotic relationship with these microbes. As the beetroot juice research illustrates, bacteria possess enzymes we don’t have but that we need in order to digest certain foods.
We each possess a unique set of bacteria; the lint in our belly button, the dirt under our fingernails, and the bacteria in our gut help define who we are, and may affect our health. If you’ve ever consumed foods that contain probiotics, such as yogurt or tempeh, than you’ve influenced your microbial community. This is a very hot field of research and product development.
How big of a boost to athletic performance does beetroot juice/nitrate cause?
Surprisingly big. In this study average power output was increased by 5 percent during the 4 km time trial and 6 percent during the 16.1 km time trial. There were no changes in oxygen consumption, indicating cycling economy was improved.
Several studies have now shown that dietary nitrate supplementation causes an improvement in exercise efficiency and an improved tolerance for high-intensity exercise. In essence, your muscles are getting better gas mileage from oxygen.
Bear in mind this research was conducted on very small numbers (usually less than 12 participants in each study) of mostly male, college-age participants. All the research was carried out in laboratory settings. Whether the benefits extend to real-world settings has not been examined.
To date, dietary nitrate supplementation has been shown to improve a number of exercise performance variables in several small studies:
- reduce the oxygen cost of submaximal cycling
- reduce the oxygen cost of low and high intensity knee extensor exercise
- reduce the oxygen cost of treadmill walking and running
- extend time-to-exhaustion during high intensity exercise
How does it work? Dietary nitrate supplementation appears to reduce the metabolic perturbation in contracting muscle cells (muscles at rest are not affected). There is a reduced rate of muscle ATP turnover at a given work rate. The mechanisms responsible for this reduced oxygen cost include increased mitochondrial efficiency (Larsen, 2011), and perhaps increased energetic efficiency of calcium transport by the sarcoplasmic reticulum Ca2+ ATPases (SERCA) (Ferreira, 2011).
The effects of dietary nitrate are not limited to athletic performance. Nitric oxide can widen (dilate) blood vessels, reducing blood pressure and increasing blood flow. Much of the current research on dietary nitrate supplementation is focusing on the prevention and treatment of conditions such as heart attacks and peripheral arterial disease (PAD). Scientists are also starting to examine the effects of nitrate on brain health.
Beetroot juice? Yuck. What other foods have high levels of nitrate?
Beetroot juice was used for the experiments because it offers a quick and easy way for research participants to consume a substantial amount of nitrate. But beetroot juice is something of an acquired taste, and it can, ahem, result in red urine and red stools.
Luckily, beetroots are just one of many vegetables and herbs that are high in nitrate. Leafy green vegetables tend to be the top sources of nitrate:
- Very high nitrate levels (> 250 mg/100 g*): arugula (rocket or rucola), bok choy, celery, chervil, collard greens, cress, lettuce, radish, red beetroot, rhubarb, spinach, Swiss chard.
- High nitrate levels (~100-250 mg/100 g): basil, celeriac, Chinese cabbage, chard, coriander, endive, fennel, kohlrabi, leek, mustard greens, parsley.
*Numbers are nitrate content, expressed as milligrams per 100 grams fresh weight, and are compiled from a variety of U.S. and European sources. Nitrate levels in vegetables can vary considerably depending on many factors, such as growing conditions.
The amount of nitrate utilized in the research studies to reduce the oxygen cost of exercise ranges from about 300-500 mg. These are levels that are readily obtained by eating a diet rich in fruits and vegetables. Here’s how some of the numbers compare:
500 ml (~17 ounces) beetroot juice 500 mg nitrate*
1 cup raw spinach 926 mg nitrate**
1/2 cup cooked collard greens 198 mg nitrate**
1 cup raw leaf lettuce 103 mg nitrate**
* The beetroot juice used in several of the experiments was supplied by James White Drinks Ltd (Ipswich, U.K.). According to the company website, approximately 2.5 beetroots are in each 250 ml serving and the juice contains 0.1 g of nitrate per 100 ml.
** These numbers are adapted from Hord, 2009. Remember that nitrate concentrations in vegetables can vary considerably.
Participants in almost all the research studies were asked to avoid foods high in nitrate, and/or performed the exercise tests after a 3 hour (or overnight) fast. Thus they started off with low levels of plasma nitrate in their systems.
What would happen if you conducted the research on participants who consumed a diet of nitrate-rich vegetables and thus would presumably have high plasma nitrate levels to begin with? Would you see improvements in athletic performance following additional dietary supplementation? It seems unlikely as there is no evidence that higher doses of dietary nitrate increase the beneficial effects (no dose-response studies have been published).
What about hot dogs?
Nitrate and nitrite are also present in very low levels (too low to impact athletic performance) in cured and processed meats such as hot dogs, bologna, corned beef, luncheon meats, sausages and ham. They are added to enhance flavor, stabilize color, and serve as antimicrobial and antioxidant agents.
Nitrate and nitrite are considered potentially harmful at high concentrations, and their levels are regulated in food and drinking water. This regulation is the source of much debate. Researchers note that the traditional Japanese diet, the heart-healthy Mediterranean diet, and the research-based Dietary Approaches to Stopping Hypertension (DASH) eating plan all emphasize fruits and vegetables, and thus are abundant in nitrate. This has led to speculation that these diets might help protect against heart disease, high blood pressure, and type 2 diabetes in part because of their high nitrate levels. For a good discussion of the dietary issues, as well as lists of nitrate levels in foods, see Hord, 2009.
What are the risks?
The nitrate-nitrite-nitric oxide pathways can be confusing. There is a big difference between the biological effects and toxicity of nitrate and nitrite. And there is a big difference between the biological effects of inorganic nitrate, found in dietary sources such as beetroot juice and vegetables, and organic nitrate, found in drugs such as nitroglycerin.
Nitrate supplementation to enhance sports performance has become a hot topic in online forums, but unfortunately there are some misconceptions. This has raised concern among leading researchers in the field, prompting them to address potential hazards (see the Journal of Applied Physiology, August 2011 ‘Letters to the Editor’ section). Recommendations include:
- Don’t use nitrate salts and nitrite salts as dietary supplements to enhance sports performance.
- Be aware that nitrite, used intentionally or unintentionally, can have harmful effects.
- Nitrate-containing vegetable juice presents a potential risk if stored incorrectly. If the juice gets contaminated by bacteria that can convert nitrate to nitrite, high levels of nitrite could accumulate over time which could potentially be harmful.
- Nitrate ingestion from dietary sources, such as vegetables, is safe.
In addition, several medications may adversely interact with a high nitrate diet. These include nitroglycerin or nitrate preparations used for angina, and PDE-5 inhibitors such as Viagra, Cialis and Levitra. Anyone with risk factors for or diagnosed with heart disease, or with low blood pressure (hypotension), may wish to consult their healthcare professional before starting a high nitrate diet. Individuals with kidney stones should bear in mind that several vegetables that are high in nitrate are also high in oxalate (rhubarb, beetroot, Swiss chard, spinach).
The bottom line: You are what you – and your microbes – eat
It’s tempting to interpret this exciting research as suggesting that a particular substance, such as beetroot juice, provides a “new secret weapon” akin to an ergogenic aid. But all the evidence points to the slightly less sexy conclusion that the true ‘secret weapon’ to sports performance resides in your vegetable crisper. (Popeye was right all along!)
Eating a diet abundant in nitrate-rich vegetables may improve your athletic performance (as well as your cardiovascular health). Conversely, consuming a diet low in nitrate-rich vegetables may adversely affect your athletic performance (and your cardiovascular health).
To improve your performance during day-to-day training and competition:
- Aim for a serving of fruits and a serving of vegetables at each meal (If you don’t know where to start, take a look at ChooseMyPlate.gov, the DASH Eating Plan and the Mediterranean diet)
- To up your odds of improving performance for a specific event, try consuming nitrate-rich foods approximately 3 hours before the event
- Ditch the mouthwash (and don’t obsess over belly button lint or dirt under your fingernails – they probably harbor friendly, helpful microbes)
- Don’t forget the big picture. Stay well hydrated and get plenty of sleep (see Twelve Everyday Health Rules from 1908)
- Consider keeping a training log so you can look for patterns among these variables and determine what works best for you.
See how easy it is to incorporate greens into your diet with these awesome recipes (and stunning photos) from around the food blogosphere:
- From Smitten Kitchen: Spinach Quiche (freezer friendly) and Arugula, Potato and Green Bean Salad
- From Kiss My Spatula: Wild Arugula-Quinoa Salad with Cherries and Thyme Roasted Baby Beets with Mint Vinaigrette
- From Love & Olive Oil: Fig, Prosciutto, and Arugula Pizza and Pizza Bianca with Goat Cheese and Greens
- From Food Blogga: Spinach and Apple Salad with Warm Cranberry-Maple Dressing and Arugula, Baby Spinach and Blueberry Summertime Salad
- From 5 Second Rule: Creamy Spinach Cashew Spread and Roasted Beet Salad with Goat Cheese and Walnuts
- Start with Dr. Allen Lim’s Rice Cakes (a favorite snack of pro cyclists) and add in chopped spinach or other greens (fresh or frozen)
- Do your own riff on the classic Joe’s Special (try rolling in tortillas and freezing) or add spinach to Freezer Breakfast Burritos (my standby is to omit the sausage, add frozen hash browns, make several dozen and freeze)
What’s your favorite recipe that uses leafy green vegetables?
Hungry for more information?
- L F Ferreira, BJ Behnke. A toast to health and performance! Beetroot juice lowers blood pressure and the O2 cost of exercise. Journal of Applied Physiology, 110:585-586, 2011. doi: 10.1152/japplphysiol.01457.2010
- NG Hord, Y Tang, NS Bryan. Food sources of nitrates and nitrites: the physiologic context for potential health benefits. American Journal of Clinical Nutrition, 90 (1):1-10, July 2009. doi: 10.3945/ajcn.2008.27131
- KE Lansley, et al. Acute dietary nitrate supplementation improves cycling time trial performance. Medicine & Science in Sports & Exercise, 43(6):1125-1131, June 2011. doi: 10.1249/MSS.0b013e31821597b4
- FJ Larsen, et al., Dietary inorganic nitrate improves mitochondrial efficiency in humans, Cell Metabolism, 13(2):149-159, February 2011. doi: 10.1016/j.cmet.2011.01.004
- JO Lundberg, et al. Roles of dietary inorganic nitrate in cardiovascular health and disease. Cardiovascular Research, 89 (3):525-532, 2011. doi: 10.1093/cvr/cvq325
- A A Kenjale, et al. Dietary nitrate supplementation enhances exercise performance in peripheral arterial disease. Journal of Applied Physiology, 110(6):1582-1591, 2011. doi: 10.1152/japplphysiol.00071.2011
The Human Microbiome Project seeks to characterize the various microbes and their DNA that reside in and on our bodies. The project is examining the connections among these microbial communities, our health, and various conditions including psoriasis, Crohn’s Disease, acne, asthma, and obesity. Also check out Belly Button Biodiversity.
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