5-a-day 'does not help breast cancer'

Increased intake of fruit and vegetables to above the daily recommended amount of five portions a day did not improve rates of survival of breast cancer, The Times reported on July 18 2007. Women “who obeyed the 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.”

This does not mean a healthy diet is no longer important for people with cancer. Although there was no difference in rates of survival between the women with breast cancer on the strict diet and those in the control group, the control group were all eating a healthy "five-a-day" (at least) diet and there was no comparison with an "unhealthy" diet.

Where did the story come from?

The story was based on reports from the Women’s Healthy Eating and Living (WHEL) study group led by John Pierce, from the University of California in San Diego. It was published in one of the top 10 peer-reviewed journals, the Journal of the American Medical Association .

What kind of scientific study was this?

This was a multi-centre randomised controlled trial which was unblinded, as the participants would have known which group they were in: those eating a normal healthy diet or those on a strict diet with increased intake of fruit and vegetables.

Three thousand and eight women who had been treated for early-stage of breast cancer during the previous four years, were randomly assigned to two groups. One group began a very intensive programme of dietary change involving trained counsellors, telephone counselling, cooking classes and monthly newsletters. 

The other (control) group were given the usual advice about healthy eating which was reinforced with printed material advising eating five servings of fruit and vegetables a day and a reduced-fat diet. Both groups had their diet assessed by telephone questionnaires and a blood test. Survival free from breast cancer and the overall number of deaths in each group were assessed over an average of about seven years.

What were the results of the study?

The researchers found that there was no difference in the number of new breast cancers, invasive breast cancers, or deaths between the groups. About 17% of women in each group developed invasive breast cancer or a new breast cancer, and 10% in each group died.

What interpretations did the researchers draw from these results?

The researchers conclude that among survivors of early-stage breast cancer, adoption of a diet that was very high in vegetables and fruit and low in fat did not reduce additional breast cancer events or mortality.

What does the NHS Knowledge Service make of this study?

A diet very high in fruit and vegetables and low in fat did not benefit women in this trial. The researchers discuss some of the implications of this result and put it in context with other research in the area. There are some other factors that may explain this lack of effect:

• The women in the untreated group were already taking what many might consider a healthy diet at the start of the study, with more than seven servings of fruit and vegetables per day and less than 30% of energy from fat. We cannot say what the effects might be if women who ate very few fruits and vegetables were compared with women who ate the recommended amount of fruit and vegetables.
• Although the intervention aimed at radically changing the diet of the treated group, only a small difference between the groups was achieved in either energy intake or weight loss, both of which have been linked with improvements in prognosis in previous trials.

This study does not mean that eating fruits and vegetables is not important, and women with breast cancer should continue to eat a healthy diet, containing the recommended amounts of fruit and vegetables.