The research which tracked more than 60,000 women over two decades found that those who ate a diet rich in fruit, vegetables, fish, nuts, whole grains and olive oil had a far lower chance of developing an aggressive form of the disease.
Every year, 53,000 women in the UK are diagnosed with breast cancer.
The major new study funded by the World Cancer Research Fund, which tracked women aged between 55 and 69 for 20 years, found that those who adhered most closely to a Mediterranean diet had a far lower chance of disease.
Overall, they had a 40 per cent reduced risk of oestrogen-receptor negative breast cancer.
Around one in three cases of breast cancer falls into this category, which is more deadly than other types of disease.
The Mediterranean Diet pattern is one that includes a high intake of plant-based proteins, such as nuts, lentils and beans, whole-grains, fish and monounsaturated fats – also known as “good fats”, such as olive oil.
This diet also has a low intake of refined grains such as white bread or white rice, red meat and sweets.
Although the traditional Mediterranean Diet involves moderate consumption of alcohol, in this study alcohol was excluded from the criteria, as this is a known risk factor for breast cancer, and linked to 12,000 cases annually.
Breast cancer is the most common cancer in women in the UK with over 53,000 new cases each year.
Around 40 per cent of all cancers are linked to lifestyle, with breast cancer risks heightened by excess weight, poor diet, alcohol and smoking.
Dr Panagiota Mitrou, Director of Research Funding at World Cancer Research Fund, said:
“This important study showed that following a dietary pattern like the Mediterranean Diet, could help reduce breast cancer risk – particularly the subtype with a poorer prognosis. With breast cancer being so common in the UK, prevention is key if we want to see a decrease in the number of women developing the disease.
“We would welcome further research that helps us better understand the risk factors for the different breast cancer subtypes.”
Professor Piet van den Brandt, lead researcher on this study at Maastricht University said:
“Our research can help to shine a light on how dietary patterns can affect our cancer risk.
“We found a strong link between the Mediterranean Diet and reduced estrogen-receptor negative breastcancer risk among postmenopausal women, even in a non-Mediterranean population. This type of breast cancer usually has a worse prognosis than other types of breast cancer”.
“This study adds to evidence that a healthy diet, full of ‘good’ low-saturated fats, plays a part in lowering risk of the disease,” she said.
“However, it’s important to remember while lifestyle choices like eating a well-balanced diet and taking regular exercise can help reduce the risk of cancer, they don’t guarantee prevention. So it’s crucial women know the signs and symptoms of breast cancer, and contact their GP with any concerns.”
Separate US research found that women already being treated for breast cancer could boost survival chances by eating a diet rich in soy.
Women with estrogen-receptor negative breast cancer who added the Japanese ingredient to their diet were able to reduce their risk of dying by up to a fifth, the study found.
Scientists founds that foods rich in isoflavones – the active ingredient in soy – appeared to boost survival.
The ingredient is found in meat replacement foods such as tofu, as well as in soy sauce, Miso soup, soy milk and edamame beans.
Study leader Dr Esther John, of the Cancer Prevention Institute of California, said: “Whether lifestyle factors can improve survival after diagnosis is an important question for women diagnosed with this more aggressive type of breast cancer.
“Our findings suggest that survival may be better in patients with a higher consumption of isoflavones.”