Women with a high-fat diet may increase their risk of developing breast cancer later in life, say researchers.
High-fat diets increased the risk
A study of more than 13,000 women from Norfolk found that women who ate the most saturated fats - such as those found in chocolate snacks and fast food - were almost twice as likely to develop cancer, compared with those who ate the least.
Many large studies have failed to find a link between fat and breast cancer, but experts say that the type of food survey used by earlier researchers may have masked the problem.
It is already known that being obese raises the risk of breast cancer, but this study points the finger at fatty foods in particular.
Writing in The Lancet medical journal, experts from the Medical Research Council's Dunn Human Nutrition Unit in Cambridge reported details of detailed "food diaries" taken from the women.
Women in the top 20% bracket for consumption of saturated fats were roughly twice as likely as women in the lowest 20% bracket to develop breast cancer.
The women had been carefully matched so that other factors which might skew the results, such as other unhealthy lifestyles, were taken into account.
Dr Sheila Bingham, the unit's deputy director, said: "The study shows there is an emerging link between eating too much fatty food and increasing the risk of breast cancer.
"The effect seems to be related particularly to saturated fat found mostly in high fat milk, butter, meat and some cereals such as biscuits and cakes."
Dr Lesley Walker, from Cancer Research UK, said: "The link between diet and cancer is a complex business.
"The study continues to uncover more information about how the two can be connected.
"This research highlights the importance of eating sensibly to reduce cancer risk."
The incidence of breast cancer in developed countries is increasing steadily - it is now the most common cancer in women in the UK.
Many more cases are now detected early because of breast screening programmes, and improvements in drug treatments are boosting cure rates.
Delyth Morgan, Chief Executive of Breakthrough Breast Cancer said: "Breast cancer is an extremely complex disease and it's difficult to research the impact of specific dietary factors, such as fat intake
alone, on breast cancer risk.
"Breakthrough would welcome any improvements in research methods which help establish with certainty, breast cancer risk factors."