Eating more fruit and vegetable and cutting out fat may lower a woman’s risk of dying from breast cancer.

In the largest trial of its kind, researchers followed almost 50,000 women over the course of two decades.

Around half were asked to slash their fat intake by around 20 per cent and consume an extra portion of fruit, veg and grains. The rest kept up with their usual diet.

Results of the major trial showed those who followed the guidance had a fifth lower risk of dying from the cancer.

Charities have praised the findings, which are to be presented at the American Society of Clinical Oncology in Chicago. The diet part of the study enrolled 48,835 women aged between 50 to 79 without breast cancer in the 1990s.

Despite the promising finding, the diet change did not lower the risk of developing breast cancer, which was the study's main goal.

Still, doctors say the results show a way women may improve their odds of survival.

Breast cancer affects one in eight women at some point in their lives in both the UK and US, statistics show.'Patients are eager for things that they can do,' said Dr Jennifer Ligibel of the Dana-Farber Cancer Institute in Boston.

'It really suggests that changing your diet, losing weight, exercising, could actually be a treatment.'

She had no role in the study, led by Dr Rowan Chlebowski of Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center.

Dr Chlebowski said: 'The balanced diet we designed is one of moderation, and after nearly 20 years of follow-up, the health benefits are still accruing.'

Dr Lidia Schapira, a breast cancer expert at Stanford University, said the results need to be taken 'very seriously'.

The study previously showed that there were fewer deaths from all causes among women in the lower fat group who later developed breast cancer.

Baroness Delyth Morgan, chief executive at Breast Cancer Care and Breast Cancer Now, praised the results of the ‘major’ trial.

She said it ‘provides strong evidence all postmenopausal women - who have not had breast cancer - can reduce their risk of dying from breast cancer’.

‘These findings are promising as they suggest that by encouraging healthy eating, we could help more women lower their risk of dying from breast cancer,’ she added.

‘While the occasional treat won’t hurt, there are many health benefits to keeping to a healthy low-fat diet.

‘Even small changes are a great start, like swapping regular sugary snacks for fruit or nuts.’

Georgina Hill, health information officer at Cancer Research UK, said healthy, balanced diet can ‘have a wide range of benefits’.

‘And this unpublished study suggests that having a healthier diet may lower the risk of dying from breast cancer.’