For week 9 journal club we looked at the following beetroot juice research paper:
Lansley KE, Winyard JF, Fulford J, et al. Dietary nitrate supplementation reduces the O2 cost of walking and running: a placebo-controlled study. J Appl Physiol 2011; 110: 591-600.
I received lots of questions for the researcher, Dr Stephen Bailey, about his research. Stephen is a lecturer in exercise physiology at Exeter University. He has very kindly answered all of our questions and you can read the responses below.
Q. Your study only used 9 participants. Did you carry out a power calculation to calculate the minimum sample size for your study? Sarah Rossiter (Sport and Exercise Physiologist)
A. Yes, we calculated the number of participants required to detect significant differences by using the effect size reported in the initial study by Larsen et al. (2007). We and others have since published a number of papers confirming these effects using 8-10 subjects. This indicates that the sample size provided an appropriate level of statistical power to detect the physiological and performance changes after beetroot juice supplementation.
Q. Is there potential for beetroot juice to positively impact intermittent exercise? Kevin L Merry (lecturer in Sports and Exercise Science at Loughborough College)
A. We have previously shown that beetroot juice supplementation can reduce the ATP cost of muscle force production during high-intensity exercise (Bailey et al., 2010, Journal of Applied Physiology, 109, 135-148). We showed that this reduced muscle phosphocreatine (PCr) utilisation and it might also have reduced muscle glycogen utilisation. Since PCr and glycogen are important substrates for anaerobic metabolism within the muscle, then a reduced utilisation of these substrates during exercise may increase the number of high-intensity bouts an individual can complete before these reserves attain low levels and performance is compromised. In addition we also showed in this study that the accumulation of inorganic phosphate (Pi) and adenosine diphosphate (ADP), metabolites that are associated with the development of muscle fatigue, was lower. Therefore the potential for sparing the limited anaerobic energy reserves and for lowering the accumulation of metabolites linked to the process of muscle fatigue after beetroot juice supplementation would be hypothesised to improve intermittent exercise performance. While this hypothesis has yet to be empirically tested, we have anecdotal evidence from team sports players who are very positive that beetroot juice supplementation is capable of enhancing intermittent exercise performance.
Q. Would you expect to see significant improvements in performance the more endurance trained the athlete? James Bray (part-time exercise physiology PhD student)
A. There is some evidence showing that the plasma nitrite and nitrate concentrations might be higher in training compared to untrained humans. Since beetroot juice supplementation is effective because of its ability to increase the plasma nitrite concentration, the scope for beetroot juice to be effective in trained athletes might be lower compared to untrained or lesser trained individuals. Alternatively, a larger dose may be needed to provoke the physiological and performance benefits observed in less training individuals in trained athletes. Moreover, trained athletes have better muscle oxygenation and since the conversion of nitrite to nitric oxide is enhanced when oxygen levels are lowered, it is possible that nitric oxide production from nitrite might be lower in this population. At the moment the literature is equivocal with regards to the ergogenic effects of beetroot juice supplementation in trained endurance athletes. It is possible that the extent to which beetroot juice supplementation is ergogenic in athletes might be dependent on the interaction between the nitrate dose, the event duration and intensity, and the training status of the athletes. Therefore, further research is required before beetroot juice supplementation can or cannot be recommended as an ergogenic aid for athletes.
Q. Should one drink beetroot juice if they experience GI issues? Perhaps the night before? Aaron Paige (Aspiring exercise physiologist and athletic trainer)
A. The subjects who have participated in our studies to date have not reported any significant GI troubles so this is likely to be uncommon following the ingestion of the volumes of beetroot juice consumed in our studies. For individuals who do experience GI issues, you could have them use the new concentrated beetroot juice shots which provide the same nitrate dose for a lower volume (70 ml rather than 500 ml). We know that plasma nitrite attains peak values 2.5 hours after beetroot juice ingestion and declines thereafter. Therefore, is someone was going to drink beetroot juice the night before, they would still need to top up, perhaps with a couple of shots, 2.5 hours before competition.
Q. When supplementing beetroot, is there a minimum time delay from seeing the effects of beetroot on performance? In your study the supplement was taken on 6 days, where others studies, I believe, have seen the effects of beetroot after 2 hours. Tom Watkiss (Sport and Exercise Physiology MSc student)
A. The plasma nitrite concentration peaks approximately 2.5 hours after consuming beetroot juice so we would not expected to see any changes less than 2 hours after drinking beetroot juice. We have shown that supplementation with beetroot juice for 15 days appears to be more effective than 6 days and a single dose ingested 2.5 hours prior to exercise, so longer supplementation may be more beneficial.
Q. In terms of practicality for athletes, is there a limit to its effects? I.e. distance of race or total of race. Tom Watkiss (Sport and Exercise Physiology MSc student)
A. We have shown that beetroot juice supplementation is effective during event durations of ~6-20 minutes, but it is not known whether this applies to longer duration athletic events. There is some evidence to show that the plasma nitrite levels decline during exercise so, while beetroot juice supplementation can elevate plasma nitrite levels, this will eventually be used up during exercise. Therefore, it might be useful during long-distance endurance events to top up with beetroot juice shots during the race.
Q. From previous experience of research with BR (Beet it), some of my participants / athletes have anecdotally stated that they struggled with the palatability of BR & saw that as a potential limiter to usage. As you conclude that the positive physiological effects are due to high content levels of nitrate & you now have a mechanism of extracting nitrate, are there any plans to examine the potential for making a more palatable, high nitrate drink to compare against the effects of BR? Dylan Merkett (Health Editor at Bupa)
A. For individuals who struggle with the palatability of beetroot juice, you could have them use the new concentrated beetroot juice shots which provide the same nitrate dose for a lower volume (70 ml rather than 500 ml). It is also important to note that it is the nitrate in the beetroot juice, not beetroot juice per se, that is responsible for the effects. Therefore, the consumption of other foods rich in nitrates such as lettuce (particularly rocket), spinach, radishes etc., could be an alternative method to provoke these responses. However, one thing that individuals should avoid is the uncontrolled consumption of nitrite and nitrate salts since this is dangerous and potential fatal (http://jap.physiology.org/content/111/2/616.long). Accordingly, dietary interventions should be used to obtain these effects.
Many thanks to everyone who asked a question and to Stephen for responding to the questions and giving us a better insight into beetroot juice and exercise.