They say for the ultimate nutrient and mineral balanced diet you should ‘eat the colours of a rainbow’ : red, orange, yellow, green, blue, indigo and violet. Can this prove difficult? Whats the reason behind the advice? I want to elaborate on this notion and highlight why it holds sound scientific rationale, with a few interesting examples. Following this advice makes for interesting shopping and creative cooking, yet very worthwhile. You’ll have to invent your own recipes, but most are best eaten raw.
All athletes know that fruit and vegetables need to be the main part of an effective diet, which is crucial for achieving the correct training effect with controlled fat loss or adequate nutrition to sustain over-loading, taper and maintenance period during the competitive season. Many of the vitamins, minerals and macro-nutrients (larger molecule compounds critical for everyday metabolic function and homeostasis) are responsible for processing the building blocks of organs and tissue in the body to maintain cells and grow into healthy systems. Luckily, many fruit and vegetables are a great source of fuel themselves with naturally digestible high levels of carbohydrate (starches) and fructose.
On the beet
This post is the first in the series on the ‘rainbow’ fruit and vegetables and how they provide nutritional benefit to athletes and in the case of beetroot (an abstract example of the colour red, ok more like deep crimson thanks to the anti-oxidant chemical beta cyanin), has potentially significant performance (ergogenic) gains in endurance sport like cycling and running.
Beetroot juice prepared from baked beetroot is fast becoming ‘popular’ as a performance aid with those looking for marginal gains in during competition. Several studies have been published which highlight any overall effect and benefits different preparations of this vegetable may or may not have on endurance. We all know it is a ‘marmite’ vegetable, you either like it or hate it, especially when pickled it has a more sour taste.
But whats the fuss all about, and is there any evidence to the claims?
Beetroot is an excellent source of folate and a good source of boron, manganese and contains betaines which may function to reduce the concentration of homocysteine, a homolog of the naturally occurring amino acid cysteine. High circulating levels of homocysteine may be harmful to blood vessels and thus contribute to the development of heart disease, stroke, or peripheral vascular disease.
Beetroot has been found to improve performance in athletes, possibly because of its abundance of organic nitrates. Dietary nitrate, such as that found in the beetroot, is thought to be a source for the biological messenger nitric oxide (NO), which is used by the endothelium to signal smooth muscle (found in veins and arteries), triggering them to relax. This mechanism is a common target for cardiovascular drugs in their treatment against heart disease. This induces vasodilation and increases blood flow, and hence are termed nitrodilators. Therefore, it is assumed that beetroot juice reduces blood pressure and the oxygen cost of exercise through the metabolic conversion of inorganic nitrate to bioactive nitrite and then nitric oxide, and improving the match between blood flow and oxygen uptake, and hence the oxygen cost of exercise.
The exact mechanism of their action is unknown, although nitrodilators cause blood vessels to dilate and in turn increases blood flow to muscles. Increased blood flow allows more oxygen and nutrients to reach the muscles. Waste products are also removed more quickly. The combined result of this is to increase the metabolic efficiency of the muscles and hence the stress placed on the heart needed to deliver sufficient blood volume.
Improved cardiac output due to decreased peripheral resistance (increased blood flow in the extremities) occurs through more dilated veins and capillaries. Nitrodilator drugs used in cardiac disease (like Sodium Nitroprusside, Glyceryl Trinitrate) also reduce systemic vascular resistance (depending on dose) and arterial pressure, which further reduces myocardial oxygen demand. Taken together, these two actions dramatically improve the oxygen supply/demand ratio potentially making exercise more efficient.
Dietary nitrate NO(3)(-) supplementation, via its reduction to nitrite NO(2)(-) and subsequent conversion to nitric oxide NO and other reactive nitrogen intermediates, reduces blood pressure and the O(2) cost of submaximal exercise in humans. Studies in rats support the hypothesis that NO(3)(-) supplementation improves vascular control and elevates skeletal muscle O(2) delivery during exercise predominantly in fast-twitch type II muscles, and provide a potential mechanism by which NO(3)(-) supplementation improves metabolic control. (Ref 1).
Beetroot juice appears to lower the oxygen cost of exercise by reducing the total ATP cost of muscle force production—the muscles use less ATP to produce the same amount of work. Beetroot juice also decreases the breakdown of phosphocreatine (the limited reserve of high-energy phosphate that resynthesizes ATP), thus lessening muscle metabolic disruption. These changes may be due to an increased efficiency of mitochondrial oxidative phosphorylation or increased efficiency of calcium transport by the sarcoplasmic reticulum Ca-ATPases.
Recently a few research groups have started to shed light on the properties of naturally occuring nitrodilators in performance cycling, with a trend towards showing a benefit…..
Acute dietary nitrate supplementation improves cycling time trial performance. Ref 2
9 club-level competitive male cyclists demonstrated an improvement in both a 4 and 16km time-trial effort after ingesting 500ml of a beetroot preparation containing 6.2 mmol of nitrates, 2.5hrs before each event. The study was randomised, using a cross-over design. This meant that although the study group was small, the cyclists served as their own controls (ie the relative difference in performance times were measured after a wash-out period and sufficient recovery). Randomised assignment of either the intervention (beetroot juice) or placebo, eliminates any systematic selection bias which may skew the results, and reduced the effects of variation between periods and carryover from the intervention by swapping the order in which the intervention and placebo are tested.
Results showed that the beetroot preparation improved time trial performance by 2.8% and 2.7% for the 4km and 16.1km respectively, with the longer distance being a much more significant difference (p<0.001, suggests the probability of observing a difference as large as this, or greater effect, is less than 1 in 1000 if it were a chance finding due to random variation alone).
Nitrate supplementation’s improvement of 10-km time-trial performance in trained cyclists. Ref 3
Subsequent to the study above, researchers questioned the effect of chronic ingestion of Beetroot juice on a 10km Time Trial performance. Using a similar randomised cross-over design as above 12 well trained cyclists were unknowingly given 140ml of an 8mmol/L (nitrate concentration) preparation of beetroot every day for 6 days or placebo (with a 14 day washout). A significant overall reduction in time (12 seconds, (1.25% decrease)) to completion was seen after the active preparation, with a corresponding small increase in power (6 Watts, (2.1% increase)), although still significant. Interestingly, submaximal VO2 values were reduced for both 65 and 45% maximal work capacity, highlighting and improvement in cycling efficiency as a result of 6 days of nitrate loading before an event.
No improvement in endurance performance after a single dose of beetroot juice. Ref 4
To improve upon the dietary practicalities of the effect that 500ml of Beetroot juice 6.2 mmol/L has on TT efforts, this group studied a single dose of a more concentrated preparation (140ml, 8.7 mmol/L) or placebo taken 2.5hrs before a 1hr time trial effort, again using a similar design in 20 well trained cyclists (1 week washout period).
Even though blood nitrite levels were considerably higher during the time trial effort after subjects had taken the beetroot preparation, time to completion, power and heart rate showed no significant differences. The negative finding may be a result of the increased protocol duration (16km vs 1hour) where any true effect may be lost in the variation and the study wasn’t sensitive enough to capture a smaller difference in effect. (Where as larger effects in small study populations may be due to chance alone).
Single and combined effects of beetroot juice and caffeine supplementation on cycling time trial performance
A combinatorial study design looking at both the combination of caffeine and beetroot juice, either intervention by itself and placebo (double dummy, no intervention) showed that beetroot juice alone (8.4 mmol of Nitate) was not ergogenic when taken 2 hours prior to a TT effort.
A Single Dose of Beetroot Juice Enhances Cycling Performance in Simulated Altitude. Ref 6
A study looking at the effects of Beetroot juice on a 16km TT effort at simulated altitude, observed that VO2 was lower during steady state exercise conducted prior and that the time trial performance was 38 seconds less when compared to placebo. This suggested that beetroot juice may be an effective ergogenic aid for compensating the negative effects of hypoxia at altitude.
Acute and chronic effects of dietary nitrate supplementation on blood pressure and the physiological responses to moderate-intensity and incremental exercise. Ref 7
A single preparation of Beetroot (5.32 mmol/L) was given prior to a ramp test performed on 8 subjects using a balanced, crossover design (not randomised or blinded). Steady-state VO2 was reduced by approximately 4% after 2.5hrs, and remained reduced for up to 15 days post test, indicating potential ergogenic effects of beetroot on cycling performance.
Influence of acute dietary nitrate supplementation on 50 mile time trial performance in well-trained cyclists. Ref 8
Beetroot supplementation was assessed for performance enhancement in 8 well-trained cyclists during laboratory-based 50 mile time-trial vs placebo. Although a reduced time to completion was demonstrated approximately 1 minute less vs placebo, this was not significant. The authors concluded that a lack of benefit in this study may have been due to the well-trained status of the subjects used, although this would reduce the generalisability of beetroot supplementation further.
Influence of nitrate supplementation on VO₂ kinetics and endurance of elite cyclists. Ref 9
This study examined if an elevated nitrate intake over 6 days would improve VO(2) kinetics, endurance, and repeated sprint capacity in elite endurance athletes. All parameters either remained the same or similar with no significant effects vs placebo. These finding were in contrast with previous results seen in moderately trained cyclists, suggesting the degree of training may confound the potential ergogenic effects of beetroot juice.
Beetroot juice and exercise: pharmacodynamic and dose-response relationships. Ref 10
In a balanced crossover design, 10 healthy men ingested 70, 140, or 280 ml concentrated BR (containing 4.2, 8.4, and 16.8 mmol NO3(-), respectively) or no supplement to establish the effects of BR on resting plasma [NO3(-)] and [NO2(-)] over 24 h. Subsequently, on six separate occasions, 10 subjects completed moderate-intensity and severe-intensity cycle exercise tests, 2.5 h postingestion of 70, 140, and 280 ml BR or NO3(-)-depleted BR as placebo (PL). Compared with PL, 70 ml BR did not alter the physiological responses to exercise. However, 140 and 280 ml BR reduced the steady-state oxygen (O2) uptake during moderate-intensity exercise by 1.7% (P = 0.06) and 3.0% (P < 0.05), whereas time-to-task failure was extended by 14% and 12% (both P < 0.05), respectively, compared with PL. The results indicate that whereas plasma [NO2(-)] and the O2 cost of moderate-intensity exercise are altered dose dependently with NO3(-)-rich BR, there is no additional improvement in exercise tolerance after ingesting BR containing 16.8 compared with 8.4 mmol NO3(-).
All readers should appraise the individual scientific merits of each study, and draw their own conclusions. Further research will hopefully clarify the situation more fully.
Even though many of the studies used different protocols, I believe a trend towards a small improvement in performance during shorter time-trial efforts may be real. The dose of nitrates in the beetroot preparation and the schedule of supplementation (either acute single preparation or multiple doses after 6 days of chronic ingestion) may determine the ergogenic effect in moderately trained individuals, taken prior to an event. The true ergogenic effect of organic nitrates on a typical cyclist will never been known, but with sound biological plausibility it may well be worth the investigating beetroot juice personally.
ARTICLE UPDATE- 1/1/14 Happy New Year!
A meta-analysis (a formal statistical appraisal of data from different studies questioning similar hypotheses) was performed on the pooled data from 17 studies examining the effect of nitrate supplementation on exercise performance.
In summary, they found that doses 300 to 600mg in a single bolus for 15 days chronic ingestion showed a significant moderate benefit on performance for time to exhaustion tests. Effect size (ES) 0.79, ranging from 0.23 – 1.35 on a 95% confidence interval (ie the range of effect with which we are 95% confident the true value lies) with a p-value = 0.006 suggesting a 1 in 167 chance of observing an effect of 0.79 if the difference was due to random variation alone.
Qualitative analysis suggested that performance benefits are more often observed in inactive to recreationally active individuals and when a chronic loading of nitrate over several days is undertaken. Overall, these results suggest that nitrate supplementation is associated with a moderate improvement in constant load time to exhaustion tasks. Despite not reaching statistical significance, the small positive effect on time trial or graded exercise performance may be meaningful in an elite sport context. Article.
For imaginative ideas to help you increase you beetroot intake check out www.lovebeetroot.co.uk
Ref 1: J Physiol. 2013 Jan 15;591(Pt 2):547-57. doi: 10.1113/jphysiol.2012.243121. Epub 2012 Oct 15. Impact of dietary nitrate supplementation via beetroot juice on exercising muscle vascular control in rats. Ferguson SK, Hirai DM, Copp SW, Holdsworth CT, Allen JD, Jones AM, Musch TI, Poole DC.
Ref 2: Med Sci Sports Exerc. 2011 Jun;43(6):1125-31. doi: 10.1249/MSS.0b013e31821597b4. Acute dietary nitrate supplementation improves cycling time trial performance. Lansley KE, Winyard PG, Bailey SJ, Vanhatalo A, Wilkerson DP, Blackwell JR, Gilchrist M, Benjamin N, Jones AM.
Ref 3: Int J Sport Nutr Exerc Metab. 2012 Feb;22(1):64-71. Nitrate supplementation’s improvement of 10-km time-trial performance in trained cyclists. Cermak NM, Gibala MJ, van Loon LJ.
Ref 4: Int J Sport Nutr Exerc Metab. 2012 Dec;22(6):470-8.No improvement in endurance performance after a single dose of beetroot juice. Cermak NM, Res P, Stinkens R, Lundberg JO, Gibala MJ, van Loon L JC.
Ref 5: Applied Physiology, Nutrition, and Metabolism, 10.1139/apnm-2013-0336. Single and combined effects of beetroot juice and caffeine supplementation on cycling time trial performance. Stephen C Lane Mr, John A. Hawley PhD, Ben Desbrow PhD, Andrew M Jones PhD, James R Blackwell, Megan L Ross, Adam J Zemski, Louise M. Burke
Ref 6: Med Sci Sports Exerc. 2013 Jul 10. A Single Dose of Beetroot Juice Enhances Cycling Performance in Simulated Altitude. Muggeridge DJ, Howe CC, Spendiff O, Pedlar C, James PE, Easton C.
Ref 7: Am J Physiol Regul Integr Comp Physiol. 2010 Oct;299(4):R1121-31. Epub 2010 Aug 11. Acute and chronic effects of dietary nitrate supplementation on blood pressure and the physiological responses to moderate-intensity and incremental exercise. Vanhatalo A, Bailey SJ, Blackwell JR, DiMenna FJ, Pavey TG, Wilkerson DP, Benjamin N, Winyard PG, Jones AM.
Ref 8: Eur J Appl Physiol. 2012 Dec;112(12):4127-34. doi: 10.1007/s00421-012-2397-6. Epub 2012 Apr 20. Influence of acute dietary nitrate supplementation on 50 mile time trial performance in well-trained cyclists. Wilkerson DP, Hayward GM, Bailey SJ, Vanhatalo A, Blackwell JR, Jones AM.
Ref 9: Scand J Med Sci Sports. 2013 Feb;23(1):e21-31. doi: 10.1111/sms.12005. Epub 2012 Oct 1. Influence of nitrate supplementation on VO₂ kinetics and endurance of elite cyclists. Christensen PM, Nyberg M, Bangsbo J.
Ref 10: J Appl Physiol (1985). 2013 Aug 1;115(3):325-36. doi: 10.1152/japplphysiol.00372.2013. Epub 2013 May 2. Beetroot juice and exercise: pharmacodynamic and dose-response relationships. Wylie LJ1, Kelly J, Bailey SJ, Blackwell JR, Skiba PF, Winyard PG, Jeukendrup AE, Vanhatalo A, Jones AM.Leave a reply →