woensdag 2 augustus 2017

Beets: Enhancing Sports Performance and Cognitive Function

Hyped by athletes and sports physiologists, beets (Beta vulgaris, Chenopodiaceae) have emerged as a trendy and promising sports performance supplement ingredient. A growing body of evidence suggests that beetroot, the taproot of the beet plant, has the potential to improve athletic performance and endurance. New research aims to pinpoint its mechanisms of action, and how it may help support body systems and impact blood pressure, heart health, and even cognitive function.

Beetroot contains a variety of health-promoting compounds, including betaines, resveratrol, and quercetin. However, studies of the potential sports performance benefits of beets have focused primarily on nitrates. The nitrates in beets are converted into nitrite, some of which is then transformed into nitric oxide, which plays a role in blood pressure regulation, cardiovascular function, and mitochondrial energy production.

Research supports certain exercise performance benefits of dietary nitrate supplementation, with several studies in recent years showing that supplementation can decrease the oxygen cost of submaximal exercise (exercise conducted at an intensity less than the maximum of which the individual is capable) and increase high-intensity exercise tolerance in recreational athletes.1,2,3 In addition, a 2011 study suggested that nitrate-rich beetroot juice can increase oxygen efficiency in submaximal cycling exercise.4

Exercise Performance
More recently, research is honing in on how and when performance is affected by consumption of beetroot. One 2017 study, led by Oliver Shannon at the Institute for Sport, Physical Activity and Leisure at Leeds Beckett University in the United Kingdom, sought to determine the effects of dietary nitrate supplementation on physiological functioning and exercise performance in trained runners and triathletes during short- and long-distance time trials. The authors measured plasma nitrite, resting blood pressure, and maximal oxygen consumption for eight trained male runners or triathletes. The subjects completed four exercise performance tests, each consisting of a 10-minute warmup followed by either a 1,500-meter or 10,000-meter treadmill time test.5 Three hours prior to each test, the athletes received either 140 mL of concentrated nitrate-rich beetroot juice or 140 mL of nitrate-depleted beetroot juice. Researchers found that nitrate-rich beetroot juice supplementation significantly enhanced performance in the 1,500-meter time trial but not for the 10,000-meter trial.

The findings, the authors wrote, suggest that beetroot juice supplementation may be ergogenic (i.e., performance-enhancing) during shorter-distance time trials at a high work rate, but maybe not during longer-distance time trials at a lower work rate. The authors also noted that the effects of nitrate supplementation are highly variable, and that that these results cannot be easily generalized to other populations or conditions and, as such, further study is warranted.

Much of the earlier research on beetroot has focused on endurance, but one new study from 2017 examined the impact of beetroot on high-intensity or intermittent-type exercise.6 The double-blind, placebo-controlled crossover study, led by Jean Nyakayiru of the Department of Human Movement Sciences at NUTRIM School of Nutrition and Translational Research in Metabolism at Maastricht University Medical Centre in the Netherlands, investigated whether six days of nitrate-rich beetroot juice supplementation would improve exercise performance in trained soccer players. Soccer players were chosen because the sport requires multiple bouts of high-intensity running and a heavy reliance on type II muscle fibers, which are thought to be the muscle group most impacted by nitrates.
The subjects (N = 32), of similar age, height, weight, and playing experience, ingested two 70-mL doses of beetroot juice (140 mL per day) containing 800 mg of nitrate or two 70-mL doses of beetroot juice placebo (with similar taste and appearance but depleted of nitrate) for six days.6 The final dose was ingested three hours prior to the exercise test. Subjects then completed two test days of high-intensity intermittent running performance using the Yo-Yo intermittent recovery level 1 (YoYo IR1) test, a measurement tool that simulates soccer-specific activities in a controlled setting.
Distance covered during the test was the primary measure of performance, although heart rate was measured continuously and blood and saliva samples were taken prior to the test. The authors found that nitrate-rich beetroot juice ingestion improved subject performance by 3.4 ± 1.3% compared to the placebo group, with higher plasma and salivary nitrate concentrations as well.
Interestingly, mean heart rates in the beetroot juice group were also lower than in the placebo group during the test. This may have implications for further study on heart function. The results demonstrate that nitrate supplementation could represent an effective nutritional strategy to improve exercise performance in soccer players, especially toward the end of a match. Further study, however, is needed to see if these same improvements can be translated to athletes at different performance levels.

Cognitive Function
Beetroot juice also may have important benefits beyond athletic performance, extending to healthy aging of the brain and cognitive function. A study published in 2016 examined whether beetroot juice might have a synergistic effect with exercise on neuroplasticity (i.e., the ability of the brain to reorganize by forming new nerve cell connections). Led by Meredith Petrie of Wake Forest University in Winston-Salem, North Carolina, the study looked at the effects of beetroot juice on the functional brain network of 26 older men (with a mean age of 65.4 years) who were randomly assigned to ingest beetroot juice or placebo for six weeks of exercise.7
Using measurements from peak metabolic equivalent capacity and resting state magnetic resonance imaging, the authors found that the community structure consistency of the somatomotor cortex (an area of the brain that controls motor signals to the muscles) was significantly enhanced in the beetroot juice group compared to placebo.7 They also noted significant differences in the secondary connections of the brain between the somatomotor cortex and insular cortex.
The authors concluded that older adults who exercised and consumed beetroot juice demonstrated greater consistency within the motor community and fewer secondary connections with the insular cortex compared with those who exercise without beetroot juice. Because of these results, the researchers wrote that subjects in “the exercise plus beetroot juice group had brain networks that more closely resembled those of younger adults, showing the potential enhanced neuroplasticity conferred by combining exercise and beetroot juice consumption.”

Conclusion
Though these studies shed more light on the benefits of beetroot juice and how dietary nitrates can improve exercise performance and tolerance, many questions remain. In addition to understanding more about when and how much nitrate-rich beetroot juice will have an impact, larger studies with more diverse populations are needed to better understand the exercise advantages and the broader health benefits of dietary nitrates. Furthermore, there is a wide variation in the nitrate content of many vegetables, including beets.8 Nitrate must also be metabolized to nitrite by oral bacteria, so oral hygiene becomes an important factor in the response to nitrate-based supplements, including beetroot juice. More safety data would also be useful to understand the effects of prolonged intake and the advantages or disadvantages of consuming dietary nitrates from beets alone, as opposed to obtaining the nitrates from other vegetable sources. —Karen Raterman

References

  1. Bailey SJ, Winyard P, Vanhatalo A, et al. Dietary nitrate supplementation reduces the O2 cost of low-intensity exercise and enhances tolerance to high-intensity exercise in humans. J Applied Physiol. 2009;107(4):1144-1155.
  2. Larsen FJ, Weitzberg E, Lundberg JO, Ekblom B. Effects of dietary nitrate on oxygen cost during exercise. Acta Physiol. 2007;191(1):59-66.
  3. Bailey S.J., Varnham R.L., DiMenna F.J., Breese B.C., Wylie L.J., Jones A.M. Inorganic nitrate supplementation improves muscle oxygenation, O2 uptake kinetics, and exercise tolerance at high but not low pedal rates. J Appl Physiol 2015;118:1396-1405.
  4. Cermak NM, Gibala MJ, van Loon LJC. Nitrate supplementation’s improvement of 10-km time-trial performance in trained cyclists. Int J Sport Nutr Exerc Metab. 2012;22:64-71.
  5. Shannon OM, Barlow MJ, Duckworth L, et al. Dietary nitrate supplementation enhances short but not longer duration running time-trial performance. Eur J Appl Physiol. April 2017;117(4):775-785.
  6. Nyakayiru J, Jonvik KL, Trommelen J, et al. Beetroot juice supplementation improves high-intensity intermittent type exercise performance in trained soccer players. Nutrients. March 2017;9(3):314.
  7. Petrie M, Rejeski WJ, Basu S, et al. Beet root juice: An ergogenic aid for exercise and the aging brain. J Gerontol A Biol Sci Med Sci. 2016. doi: 10.1093/gerona/glw219.
  8. Nuñez de González MT, Osburn WN, et al. A survey of nitrate and nitrite concentrations in conventional and organic-labeled raw vegetables at retail. J Food Sci. May 2015;80(5):C942-949.


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