Eating a Mediterranean diet, rich in fruit, vegetables, fish and olive oil, may help prevent breast cancer returning, according to a study presented at a major international cancer conference.

Lifestyle – whether people are physically active or not – and being overweight are known risk factors for breast cancer, but there is increasing interest in whether particular eating habits play a part in its occurrence and recurrence.

The study presented at the American Society of Clinical Oncology (ASCO) meeting in Chicago is a trial in Italy which compared the outcomes for 307 women who had been treated for early breast cancer. One group of 199 women were asked to eat a Mediterranean diet, involving four portions of vegetables, three pieces of fruit and one serving of grains a day, together with four or more servings of fish each week, some red and processed meat and plenty of olive oil. They were allowed up to one alcoholic drink a day.

The other group of 108 women were asked to eat their normal diet, but given advice on healthy food by a dietician.

The cancer researchers at Piacenza hospital, Italy, found that after three years, 11 women from the group eating a normal diet suffered a return of their breast cancer, while none of those eating a Mediterranean diet did.

Experts say the study is small and has limitations, but raises issues of great interest. “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,” said Dr Erica Mayer, an ASCO expert in breast cancer, assistant professor at Harvard Medical School and director of clinical research at the Dana-Farber Cancer Institute in the US.

But the results of studies to date have been conflicting. “It is not clear whether there is a specific diet or foods to eat or not to eat to prevent recurrence,” she said. Physical activity, on the other hand, is very beneficial, helping to prevent cancer both occurring and recurring.

The signals so far from research into women’s eating habits and breast cancer “probably reflect weight loss rather than diet”, she said. On this particular study there were issues with the methodology. “They don’t say if this is randomised. People were asked to participate in one diet or the other. There is no information about the activity level or change in weight which for most of the lifestyle research one needs to be aware of,” she said.

Cancer charities said more research was needed. “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,” said Prof Arnie Purushotham, Cancer Research UK’s senior clinical adviser. “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.”

Lady Delyth Morgan, the chief executive of Breast Cancer Now, said: “This study adds to increasingly interesting discussions about how lifestyle factors might influence breast cancer recurrence. However, we still don’t have enough evidence to demonstrate a strong link between any specific food type and a person’s breast cancer returning.

“We need to see results from longer-term studies before we can give specific diet advice to breast cancer patients. In the meantime we do know that a varied, balanced diet for general health and well-being, as well as being physically active, can be beneficial to breast cancer patients.”