Studies have shown that a single intake or a short term (3-6 days) supplementation of beetroot juice shortens your time on a time-trial event and allows you to tolerate high intensity exercise much better. This is because beetroot contains nitrates (NO3-).
Your body absorbs NO3- and secretes it into your saliva, where your mouth bacteria transform it into NO2-, which is then taken up by your stomach as you swallow. (That is why beetroot has no effect if you use antibacterial mouthwashes.) NO2- becomes NO in tissues which are in need of oxygen, such as working muscles.
NO dilates blood vessels and makes your body more efficient at using oxygen to produce energy. It also improves the contractibility of your muscle fibres.
This is great news, not only for athletes, but also for the elderly who have a reduced aerobic capacity, and for people suffering from hypertension as it will lower their blood pressure.
However, there is a problem. Most studies showing a benefit have been done on sedentary or moderately fit people. Studies on elite athletes on the other hand, are rather disappointing.
To try to understand this better, Simone Porcelli and her colleagues have studied the effect of beetroot juice on 21 young men of different aerobic fitness levels. The VO2 max values of the participants ranged from 28.2 ml/kg/min (sedentary people) to 81.7 ml/kg/min (elite level).
The researchers tested their fitness by a run to exhaustion, a series of 6-min sub-maximal runs on the treadmill, and a 3 km time trial. All the participants performed the tests twice, once after taking 500 ml/day beetroot juice for 6 days and once after drinking the same amount of a placebo for the same time.
There was an inverse relationship between the VO2max of the participants and the benefits of taking beetroot juice. In other words: the participants with the highest VO2max showed the least benefits, while those with the lowest VO2max benefitted most. The researchers also measured the blood levels of NO3- and NO2- of the participants, and noted that the fitter ones showed a smaller increase after drinking beetroot juice.
These results are not easy to explain, and Simone Porcelli and her colleagues have come up with 3 possibilities:
1) NO2- is mainly transformed into NO when tissues need oxygen. Elite athletes will have more blood vessels in their muscles due to many years of training, and it is therefore possible that the right conditions to form NO happen only rarely.
2) Athletes might take in much more nitrates with their normal diets, as they are likely to eat more than sedentary people. In this case the supplements would not matter anymore, and could just end up in their urine. Unfortunately, the researchers did not check the urine levels.
3) Our bodies can also make NO via a completely different pathway, without the need of any dietary NO3-. It is possible that many years of training have optimised this system and fine-tuned the athletes’ metabolism, making nitrate supplements superfluous.
The researchers noticed a higher NO3- and NO2- blood level in the fittest participants before taking any juice, which makes one of the two last possibilities (or both) more likely than the first one.
Whatever the reasons, if beetroot juice does not work for you, you should be happy!
photo credit: <a href=”http://www.flickr.com/photos/24987280@N00/2631746551″>Beetroot</a> via <a href=”http://photopin.com”>photopin</a> <a href=”https://creativecommons.org/licenses/by-sa/2.0/”>(license)</a>