Eating very large amounts of fruit and vegetables does not improve the survival chances of women with breast cancer, scientists have found.

A study of more than 3,000 women who had been treated for the disease showed that boosting fruit and vegetable consumption way beyond normal guidelines did not help them to live longer. Women who obeyed the super-strict eating rules imposed by scientists over seven years were just as likely to die or suffer a recurrence of breast cancer as those on a healthy “five-a-day” diet. In about 17 per cent of cases in both groups the cancer returned and 10 per cent of the women died.

Half the patients were placed on a low-fat diet which included five servings of fruit and vegetables a day.

The other half were asked to make enormous changes to their diet. As well as limiting the fat they consumed to no more than 20 per cent of total calories, they were expected to eat five servings of vegetables, plus 470 millilitres of vegetable juice, three servings of fruit and 30 grams of fibre a day.

Many women in the intervention group found the regime tough – but after four years they were consuming on average 65 per cent more vegetables, 25 per cent more fruit, 30 per cent more fibre and 13 per cent less fat than their colleagues on the easier “control” diet.

However, the results published in the Journal of the American Medical Association showed that all the extra effort was in vain.

Professor Marcia Stefanick, from Stanford University School of Medicine in California, who led the Women’s Healthy Eating and Living (WHEL) study, said: “I was really surprised and, frankly, a little disappointed by the results. We expected the twofold increase in vegetables and fruits, plus the increased fibre and reduced fat, to make a difference in the recurrence rates.”

However, she pointed out that rates for the recurrence of breast cancer in the control group were much lower than expected. At the start, the researchers had anticipated that 30 per cent of the “five-a-day” dieters would suffer a relapse.

She said many of the women had already adopted a healthier diet than the average American. “I would certainly hope that people don’t interpret these results as evidence that eating a lot of vegetables doesn’t make a difference in breast cancer,” she said. “What it shows is that getting more than the recommended amounts doesn’t change the recurrence rate for women who have already had treatment for early-stage breast cancer.”

Previous animal studies have shown that plant-derived foods contain anticancer agents. Research also suggests that high-fat diets might be linked to increased cancer risk.

The WHEL study was the largest trial ever undertaken to assess how diet affects breast cancer recurrence.

Co-researcher Dr Cheryl Rock, from the John Moores Cancer Centre at the University of California, San Di-ego, said: “We recognise that several other studies have shown clearly that eating more than five fruits and vegetables a day can make major differences in disease risk, such as in lowering blood pressure and reducing risk of stroke and heart disease.”

Liz Baker, science information officer at Cancer Research UK, said: “This study certainly doesn’t mean that women who have had breast cancer should stop eating fruit and veg.”

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