Research on more than 300 women with early-stage breast cancer reinforces earlier work which suggests diet may play an important role in cutting cancer risk.
Presented at the American Society of Clinical Oncology (Asco) conference in Chicago, the study involved 199 women eating their normal diet and 108 who ate a Mediterranean diet.
A Mediterranean diet includes vegetables, fruit, nuts, seeds, fish, olive oil and whole grains, while being low in red and processed meat, and with alcohol kept to a minimum.
People who are considered to get maximum benefit from the diet have less than one drink a day for women, or one to two for men, and fewer than three servings of red meat per day.
They also eat several servings of fruit and vegetables per day, one serving of wholegrains and up to four servings of fish per week.
In the latest study, carried out at Piacenza Hospital in Italy, women who were in remission from breast cancer were tracked for three years.
The results showed that during that time, 11 patients suffered cancer again who were following their normal diet, while no women in the Mediterranean diet group experienced a relapse.
Research published last year in the journal JAMA Internal Medicine also found that eating a Mediterranean diet supplemented with extra virgin olive oil was associated with a lower risk of breast cancer.
The study, led by the University of Navarra in Pamplona and the Spanish Biomedical Research Centre in Physiopathology of Obesity and Nutrition in Madrid, Spain, compared women whose families consumed one litre a week of olive oil, compared with women on a low fat diet.
Of more than 4,000 women, researchers found that those on the Mediterranean diet with extra olive oil appeared to have a 68% reduced risk of breast cancer.
Responding to the latest Italian study, Samia al Qadhi, chief executive of Breast Cancer Care, said: "For many women with breast cancer, fear of the disease returning is one of the biggest issues they face after treatment.
"So anything that helps us understand how to lower risk of recurrence in women who follow a Mediterranean diet rich in fish and olive oil is a welcome addition to our toolbox.
"However, this is a small study which only followed women for three years. We look forward to seeing results of longer term studies.
"Lifestyle choices like eating a well-balanced diet, taking regular exercise and maintaining a healthy weight can all help reduce the risk of cancer coming back, but they can't prevent it completely."
Professor Arnie Purushotham, Cancer Research UK's senior clinical adviser, said: "The preliminary results of this small study suggest that a Mediterranean diet could lower the risk of breast cancer returning, but we'd need much longer follow-up than three years to confirm the diet's impact.
"Further studies with more women are needed to understand more about the impact that diet can have on breast cancer survival and the biological reasons behind this."
Dr Erica Mayer, Asco's breast cancer expert, said: "The whole topic of lifestyle interventions for breast cancer survivors is a very important one.
"There is substantial research going on into what we should be recommending to breast cancer survivors."
But she said studies to date have been conflicting and the latest study had some problems with its methodology.
"It is not clear whether there is a specific diet or foods to eat or not to eat to prevent recurrence," she said.
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