The sports supplement market is big business, but the reality is that most of these supplements have little evidence for a benefit. It is not all negative news though as there is a small group of supplements that are backed by science and which can play a performance-enhancing role in some athletes. In this series on sports supplements, I will profile this group of supplements and for this podcast, the spotlight is on beetroot juice.
Now if you don’t follow the world of sports supplement research very closely, your reaction to knowing that athletes are chugging down shots of beetroot juice may be along the lines of: “What sorcery is this?” But this is not some faddish trend like Rubik’s cubes, finger spinners or activated almonds. There is now good science to show that beetroot juice, or more specifically a group of compounds found in beetroot and other vegetables called nitrates, can have a significant benefit on sports performance.
Nitrates are inorganic compounds found in many vegetables such as spinach, celery, radishes, and lettuce, but beetroot is one of the highest sources. Nitrate contributes to the production of nitric oxide, which has an important role to play in immune function as well as regulating the tone of blood vessels which impacts blood pressure and blood platelet accumulation.
Nitric oxide is a potent vasodilator, meaning it improves blood flow and oxygen delivery to working muscles. Once consumed, nitrate is converted to nitrite, which circulates in the blood. When oxygen availability is low as can occur during exercise, nitrite can be converted to nitric oxide. Nitric oxide improves the muscles’ efficiency in using oxygen. Nitric oxide also augments exercise performance by an enhanced function of type II muscle fibres which are the fast-twitch muscles used in powerful bursts of movements like sprinting. And finally nitrate, through nitric oxide, can result in a reduction in the energy cost of muscle contraction and increased efficiency of mitochondrial respiration. That all means the muscles are finely tuned for explosive power when oxygen levels are limited.
So, will drinking beetroot juice improve athletic performance? With several dozen exercise studies looking at beetroot juice and nitrates and sports performance now published, the results are looking very promising. In fact, nitrates were one of the few supplements to get the tick for having good evidence behind it in the 2018 IOC Consensus Statement on dietary supplements for use by high-performance athletes and I’ll link to this document in the show notes https://bjsm.bmj.com/content/52/7/439
So, let’s go over a summary of those benefits. Athletes who supplement with beetroot juice which contains an adequate amount of nitrate, on average gain a small benefit on exercise endurance. The most commonly studied exercise situations have been cycling and running trials from about 4 to 30 minutes in duration. At an elite level, clinical trials show a small, but competitively meaningful benefit in time trial performance. Recreational athletes seem to gain an even greater benefit from beetroot juice, which could be because of less prior adaptation of their cardiovascular system to exercise.
Supplementation is also seen to improve performance in high-intensity, intermittent, team-sport exercise of 12 to 40 minutes in duration.
Taking on extra nitrate in the form of beetroot juice can improve the exercise economy of athletes when working at a constant load while running or biking, which translates into a slightly longer time until exhaustion. So, for endurance athletes, this could convert into a small competitive advantage.
Beetroot juice appears to have little effect on power output but seems to reduce the rate of fatigue seen with continued muscle contractions. That means beetroot juice has the most benefit in exercise ranging from 1 minute up to 10 minutes or for muscular endurance events such as sports requiring anaerobic intervals such as football, hockey or rugby, and CrossFit-type exercises.
Typical doses of nitrate used in research studies have been in the ballpark of 400 mg. This dose can be provided by a single-serve of a commercial beetroot juice 'shot' of about 70 mL taken about 2 to 3 hours before exercise.
The highest dietary sources of nitrate are beetroot, celery, lettuce, and spinach. They contain about 250 milligrams of nitrate per 100 grams, but levels can vary hence the popularity of the commercial beetroot shots. And even though beetroot juice can be made at home with a juicer the concentrated shots are generally more popular owing to the much lower volume required than DIY juices. For the same amount of nitrate as you would get in a commercial 70 mL beetroot shot, you would have to chug down about half a litre of beetroot juice, which may not be too appetising an hour before a race.
As a side note, athletes using beetroot juice should avoid using mouthwash or gum as they reduce the bacteria available in the mouth that are essential for the conversion of nitrate to nitric oxide.
Side effects
There is little concern about harmful effects from taking beetroot juice apart from some occasional minor gastrointestinal upsets. As anyone who has tried beetroot juice will tell you though, be prepared for a ‘colourful surprise’ on visits to the bathroom – what goes in purple comes out pink. But this pink colouration of the urine and stools is temporary and harmless.
Beetroot juice is one of the few nutritional supplements for which research has consistently shown a sports performance benefit. The use of all supplements and sports foods by athletes though involves a balance between the potential benefits set against potential risks such as health side-effects, anti-doping rule violations from contamination, and redirection of resources from real performance-enhancing factors. So, take this into account when considering taking any sports supplement. And seek out personalised advice from a sports dietitian. You can connect with an Accredited Sports Dietitian as well as access a great range of resources through the website of Sports Dietitians Australia at www.sportsdietitians.com.au
So that’s it for today’s show. You can find the show notes either in the app you’re listening to this podcast on if it supports it, or else head over to my webpage www.thinkingnutrition.com.au and click on the podcast section to find this episode to read the show notes.
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I’m Tim Crowe and you’ve been listening to Thinking Nutrition.