Nitrates seem to be the key ingredient in beetroot
Drinking beetroot juice boosts stamina and could help people exercise for up to 16% longer, a UK study suggests.
A University of Exeter team found nitrate contained in the vegetable leads to a reduction in oxygen uptake - making exercise less tiring.
The small Journal of Applied Physiology study suggests the effect is greater than that which can be achieved by regular training.
Beetroot juice has previously been shown to reduce blood pressure.
The researchers believe their findings could help people with cardiovascular, respiratory or metabolic diseases - and endurance athletes.
They focused on eight men aged 19-38, who were given 500ml per day of organic beetroot juice for six consecutive days before completing a series of tests, involving cycling on an exercise bike.
On another occasion, they were given a placebo of blackcurrant cordial for six consecutive days before completing the same cycling tests.
After drinking beetroot juice the group was able to cycle for an average of 11.25 minutes - 92 seconds longer than when they were given the placebo.
This would translate into an approximate 2% reduction in the time taken to cover a set distance.
The group that had consumed the beetroot juice also had lower resting blood pressure.
The researchers are not yet sure of the exact mechanism that causes the nitrate in the beetroot juice to boost stamina.
However, they suspect it could be a result of the nitrate turning into nitric oxide in the body, reducing how much oxygen is burned up by exercise.
Study researcher Professor Andy Jones - an adviser to top UK athlete Paula Radcliffe - said: "We were amazed by the effects of beetroot juice on oxygen uptake because these effects cannot be achieved by any other known means, including training.
"I am sure professional and amateur athletes will be interested in the results of this research.
"I am also keen to explore the relevance of the findings to those people who suffer from poor fitness and may be able to use dietary supplements to help them go about their daily lives."
Professor John Brewer, an expert on sports science at the University of Bedfordshire, said: "These findings are potentially exciting for many people involved in sport and exercise, but will almost certainly require further more extensive studies before the exact benefits and mechanisms are understood.
"We must also remember that exercise and training and a sensible diet will always remain as the essential ingredients for a balanced and healthy lifestyle."
Dr Simon Marshall, of the University of San Diego, has carried out work on exercise and health.
He said much more work was needed involving many more subjects to draw firm conclusions.
"Certainly, a diet high in nitrate-rich fruits and vegetables is good for your heart health and this study provides further evidence of this."