Eating watercress every day could help protect against cancer, say researchers.
The vegetable reduces damage to DNA in cells, according to a British trial.
Some nutritionists claim higher intakes of 'superfoods' - including cruciferous vegetables such as watercress and broccoli - can improve the body's defences against cancer.
But specialists in the disease have sounded a note of caution, warning that consumers are being misled into thinking that superfoods will prevent them contracting cancer, rather than reducing the risk.
Blood tests were taken at the start and end of the trial, which was carried out by researchers from the University of Ulster.
The tests showed a 23 per cent reduction in DNA damage to white blood cells - which is regarded as a marker for susceptibility to cancer - among the watercress eaters. <b1>
When the same cells were exposed to damaging free radicals, scientists observed a 10 per cent cut in damage compared with cells of those eating a normal diet. They also found a rise of up to 100 per cent in levels of anti-oxidants, chemicals which help cells to defend themselves against damage.
The research, which was funded by British watercress suppliers, found smokers gained most from a watercress-rich diet - probably because the habit depletes anti-oxidants.
Professor Ian Rowland, who led the study, said the results were 'highly significant' because they were found in a real life situation.
Most previous research in the area has been conducted in test tubes or in animals, using chemicals derived from cruciferous vegetables.
He said benefits were slightly reduced for those eating cooked watercress - such as actress Elizabeth Hurley, who has been known to drink seven cups of watercress soup a day.
But Karol Sikora, professor of cancer medicine at Imperial College London, said the findings of the study were 'grossly overstated'.
He added: 'We know that fruits and vegetables all do affect DNA damage, hence the five-a- day strategy to prevent cancer.
'There is absolutely nothing special about watercress. I don't think people will seriously convert to eating 85g of the stuff each day. That's an awful lot of cress!
You might even turn green. Much better to look holistically at your diet and ensure that there's plenty of fruit and vegetables, fibre and as little fat as possible.'
Dr Anthea Martin, of Cancer Research UK, said: 'While the results of this study are interestingit involved a relatively small number of people.
'Larger studies are needed to determine whether the effects of watercress on cells seen by the researchers translate into a decreased risk of developing cancer'.