Nitrate content in beetroot juice increases tolerance to exercise

Writing in the Journal of Applied Physiology​, the University of Exeter researchers wanted to find out if the physiological affects that beetroot juice (BR) has during physical activity could be attributed to the nitrates it contains and not to the presence of other potentially bioactive compounds.

Reduced oxygen uptake​

Previous research has demonstrated the positive effect of beetroot juice on the body during exercise.

Professor Andy Jones, the senior scientist on the study, was part of pioneering research from the same university that claims BR can allow people to exercise for up to 16 per cent longer.

The vegetable juice’s nitrate content may reduce oxygen uptake to an extent that cannot be achieved by any other known means, making exercise less tiring, according to the 2009 findings.

The Exeter scientists claim their latest study is the first to investigate the effects of BR and nitrate-depleted beetroot juice (PL) on physical activity.

The results showed that six days of BR supplementation enhanced the participant’s overall performance and heart function during exercise.

Methodology and results​

Nine healthy, physically-active male subjects were assigned in a randomised, double-blind, cross-over trial.

The scientists compared changes between the BR and PL supplementation on a range of physical activity measures such as blood pressure and mitochondrial oxidative capacity (Qmax), which is a measure of how efficiently the muscles use oxygen.

The study began with an assessment of the individuals involving treadmill tests, maximal oxygen intake, blood pressure, heart rate, lung function and blood nitrite concentration.

The participants were then randomised to receive 0.5L per day of either BR containing 6.2 mmol of nitrate or PL (containing 0.003 mmol of nitrate) for six days.

Subjects took part in repeat treadmill exercise tests on days four and five. On day six, the men were asked to perform knee extension tests while scans were taken of their body.

The knee extensions were designed to reduce muscle phosphocreatinine concentration (PCr) and allow them to estimate Qmax. Phosphocreatinine is a molecule that acts as a rapidly mobilizable reserve of high-energy phosphates in skeletal muscle and brain.

Tests were repeated during a second supplementation period when the men received the alternative drink for six days.

Results showed that, compared to PL, BR elevated the men’s plasma nitrate concentration and reduced their systolic blood pressure.

The participant’s oxygen requirements during treadmill walking, moderate-intensity running and severe-intensity running were also reduced by BR. Time-to-exhaustion was increased by 15 per cent by BR during severe-intensity running.

There was no difference in Qmax between PL and BR.

“These results indicate that the positive effects of six days of BR supplementation on the physiological responses to exercise can be ascribed to the high nitrate content,”​ said the researchers.

Source: Journal of Applied Physiology​

“Dietary nitrate supplementation reduces the O2 cost of walking and running: a placebo-controlled study”​

Authors: K. E. Lansley, P. G. Winyard,​J. Fulford, A. Vanhatalo, S. J. Bailey, J. R. Blackwell, F. J. DiMenna, M. Gilchrist, N. Benjamin, and A. M. Jones