Supplementing with sodium nitrate has been shown to improve exercise capacity. Yet sodium nitrate in processed foods is a health hazard. New research suggests that you might be able to eliminate those health risks yet still reap the performance benefits by eating beets before exercise.
Eating a diet rich in vegetables is one of the best ways to decrease your risk for chronic diseases like heart disease and cancer. Vegetables are low in calories but high in fiber, vitamins, minerals, antioxidants, and phytochemicals.
But what about the nitrate content? Would that be on your list? When it comes to exercise, mounting evidence shows the nitrate content of vegetables may exert a natural ergogenic — or performance-enhancing — effect.
Nitrates are found in all vegetables but are especially abundant in leafy green vegetables and in beetroot.
Okay, but aren’t nitrates also found in hot dogs and bacon, and aren’t these foods supposed to be bad for you?
Nitrate versus nitrite
What a difference a vowel makes!
Sodium nitrate (note the “a”) is a naturally occurring compound found in almost all leafy green vegetables as well as in beetroot. For a list of foods high in nitrates see the Research Review “Do Veggies Improve Endurance Performance?” Sodium nitrate has antimicrobial properties so it’s used as a food preservative in lunch meats, sausage and bacon. When it combines with the myoglobin in meat it increases the meat’s colour during cooking. Sodium nitrate is also one of the ingredients in pesticides, fireworks and fertilizers.
Sodium nitrite (note the “i”) is a close relative of sodium nitrate and is also used as a preservative, but some of its byproducts have been linked to cancer and other serious health conditions. Because of this, the USDA, EPA and WHO have all placed limits on the amount of nitrates and nitrites that are added to food and water.
Here’s the catch: Dietary nitrates and nitrites seem to be harmful… except when consumed in their naturally occurring vegetable form. (Just one more reason to eat whole, unprocessed foods.) So don’t run out and load up on bacon and hot dogs to increase the amount of nitrate in your diet.
Beets and performance
Back to dietary nitrate and improved exercise performance. A number of studies show that beetroot juice improves time to exhaustion during exercise (in other words, you have more energy for a longer period) and reduces the oxygen cost of exercise (1, 2).
Researchers have hypothesized that the nitrate in beetroot juice reduces the oxygen cost of endurance exercise by allowing you to burn less energy (ATP) to produce the muscular force that propels you forward, allowing you to last longer.
So how does this all work?
Beets contain a lot of great things, including phytochemicals like quercetin and resveratrol. But the positive effects of beets on exercise performance are probably due to their nitrate content.
The breakdown and use of dietary nitrates in the body is actually pretty cool. It begins in the mouth with your saliva. About a quarter of the dietary nitrate (NO3) found in foods like beets enter the salivary circulation after combining with bacteria on your tongue. There, the NO3 is converted to active nitrite (NO2). Neat, huh? Then you swallow the nitrite and it is reduced to nitric oxide (NO) when it interacts with your stomach acid.
It is this form, nitric oxide, that produces the positive effects during exercise. You’ve probably heard of nitric oxide, especially if you hang out in the supplement aisles of your local health food store. Nitric oxide does a lot of things, but in terms of exercise it increases blood flow to the muscles, making it easier for your power generators (mitochondria) to produce energy (ATP). It also governs blood pressure and regulates muscle contraction.
The majority of beetroot studies so far have used time to exhaustion protocols – and those results don’t always translate into actual performance gains. What most enquiring minds really want to know is: will eating beets or drinking beetroot juice help me to run (cycle, swim, walk, etc) faster?
One study showed that drinking beetroot juice improves cycling time trial performance (3), but what about eating plain ol’ beets – and what if you are a runner, not a cyclist?
The study in this week’s review looked at whether eating 200 grams of whole beetroot (containing ~500 mg of nitrates) before exercise improves running performance during a 5 km treadmill time trial.
Murphy, M., Eliot, K., Heuertz, R., Weiss, E. Whole beetroot consumption acutely improves running performance. J Acad Nutr Diet. 2012 Apr;112(4):548-552.
The participants in this study consisted of five recreationally fit men and six women in their 20s. The study used a double-blind crossover design in which the subjects ate either 200 grams of baked beets or a placebo (cranberry relish) before completing a 5 kilometer treadmill time trial test. All participants completed two trials in random sequence separated by a 1-week “washout” period. The purpose of the washout was to decrease the chances that the intervention effects (eating beets or cranberries) would overlap and interfere with the results of either of the trials.
Trial 1: The subjects ate 200 grams of baked beets (about 2 medium-sized beets) and 75 minutes later ran 5 kilometers on a treadmill.
Trial 2: The subjects ate 200 grams of a cranberry relish and 75 minutes later ran 5 kilometers on a treadmill.
For each of the trials, the subjects arrived at the laboratory after an 8 hour fast. They were asked to avoid eating other nitrate-rich foods (they were given a list), dietary supplements, and medications for 72 hours before the test. They were also told not to lift weights in that same time period and in the 24 hours before were asked not to consume alcohol, caffeine or do any sort of exercise. All these “rules” made for a stronger study by levelling the playing field as best as possible between subjects.
While it is pretty easy to distinguish the taste of beets from that of cranberry relish, the researchers kept the portions and calories similar and used the same spices. Because the participants didn’t know what the study was about, the researchers thought it unlikely that the difference in taste would create a placebo effect and change the outcome of the study.
Resting blood pressure was measured before and one hour after eating the beetroot or cranberry relish. During the time trial the researchers recorded average running velocity, heart rate and rating of perceived exertion at one mile intervals and at the end of the 5 km run.
Improved running performance
The researchers wanted to find out if eating 200 grams of beetroot (containing ~500 mg nitrates) before exercise improved running times enough to be significant. What they found was that yes, average running velocity (speed in a given direction) was slightly faster (3%) after eating the beetroot compared to the placebo 12.3+ 2.7 vs 11.9+ 2.6 km.
Interestingly, the difference was greatest (5%) during the last mile.
While the difference may not look like much, a 3% faster running velocity translates to about a 41 second faster finishing time. In a short race like a 5 km run, 41 seconds is a lot! For example if your pace is 8 minutes per mile, you would finish a 5 km in 24:51 minutes. But if you ate 200 grams of beetroot before the run you could potentially shave 3% off of your time.
So we know the subjects ran at a faster velocity. But were there any differences in heart rate or did they feel like the run was easier after eating the beetroot?
Heart rate and rating of perceived exertion
Even though the subjects ran at a slightly faster velocity during the beetroot trial, there were no differences in exercise heart rate compared to the placebo trial.
What does that mean?
Well, the most likely explanation is that the nitrate content of the beets reduced the oxygen cost of exercise. Unfortunately, this study did not take direct measurements of oxygen use or of respiratory exchange rate (RER is a measure of the ratio of carbon dioxide produced to oxygen used) so this doesn’t fully prove cause and effect. However, it does support the results of similar types of studies evaluating the performance effects of dietary nitrates.
Perceived exertion was measured using the Borg 6 to 20 point scale. Perceived exertion was rated lower during the first mile of the beetroot trial with no differences later in the run. If perceived exertion was lower during the first mile of the beetroot trial this may have contributed to the faster running velocity later in the run, perhaps because the subjects didn’t feel as tired.
A major limitation of this study is that serum nitrate levels weren’t measured, so there is no way to know how great an increase there was after eating the beetroot compared with the placebo. Also, the nitrate content in the beetroot was not measured. Still, given what we know about the nitrite content of beets, it is pretty likely that the beetroot did in fact increase serum nitrate levels and enhance performance.
Eating 200 grams of baked beets 75 minutes before exercise improved the running performance of recreationally fit men and women.
The increase in performance was most likely due to the conversion of the dietary nitrate to nitrite to nitric oxide in the body. Nitric oxide reduces the oxygen cost of exercise by requiring your muscles to use less energy or ATP to produce the same amount of work.
What this means is that eating a couple of medium sized beets at least 60 minutes before a run could help you shave at least half a minute off of your 5 km time!
Of course, this was a very small study. If you want to help out with your own science project, why not try it yourself? At minimum, it’s worth a shot to see if it makes a difference. (Just don’t be alarmed if you’re peeing pink for a little while.)
- The results of this study have some real value and potential application to the athletic setting. Most previous studies evaluating the performance effects of nitrate-rich vegetables have used time to exhaustion protocols (which test exercise capacity, rather than athletic performance).
- You can try this yourself! If you are a juice fan, you could easily juice a couple of beets and drink the juice down before your morning run and see how you feel. Just make certain you stick to real foods. Don’t risk your life by supplementing with nitrite salts.
- We still need more research to determine the optimal amounts of dietary nitrate needed to enhance athletic performance.
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