Dietary fat and breast cancer
The analysis - which included 25,000 cases of breast cancer from 45 separate studies - also found an association between high meat consumption and the risk of developing the disease.
Previous research on the effects of dietary fat has produced conflicting and confusing results. But the new Canadian report suggests the relationship between breast cancer and dietary fat may be independent of obesity or high calorie consumption, reinforcing the need for a healthy, balanced diet.
Scientists at the Ontario Cancer Institute in Canada reviewed all the published literature on dietary fat and breast cancer and combined results from 45 different studies, employing a range of methodologies. The data included 25,000 breast cancer patients and over 580,000 healthy women worldwide.
They took into account other known and suspected risk factors for breast cancer and compared women with the highest and lowest fat intake, in order to assess whether or not dietary fat was contributing to the disease.
Women who ate high amounts of saturated fat were on average around 20 per cent more likely to develop breast cancer than low consumers of fat. Eating large amounts of monounsaturated fats increased risk by about 10 per cent - a non-significant difference - while overall fat consumption was related to a small, but statistically significant increase in risk of 13 per cent.
Researchers also found a small significant increase in risk with high meat consumption. Women who ate large amounts of meat were 17 per cent more likely to develop breast cancer than those who ate little or none.
Dr Norman Boyd, lead researcher on the study, "We already know that being obese can increase the risk of a range of cancers, but evidence is building that eating large amounts of fat, particularly the saturated kind, can independently increase risk.
"Our analysis of all the available research suggests there is indeed an association with saturated fat and breast cancer. The increase in risk seems fairly modest, even among very high consumers of fat, although the difficulties in measuring dietary intake mean we could be under-estimating the true scale of the effect.
"In any case, the effect seems to be over and above the increase in risk from obesity and underlines the message that high consumption of fat is bad for your health."
Scientists from Cancer Research UK and the Medical Research Council recently found that one of the common methods used to measure fat in the diet may have been helping to obscure its effect on breast cancer2.
When they asked people to remember the foods they had eaten using food frequency questionnaires, they found only a small increase in risk with dietary fat, but the effect of fat seemed to be much larger when they used food diaries to record diet on a daily basis. The new analysis combined data from both kinds of study and has strengthened the evidence that fat and meat consumption can contribute to breast cancer.
Dr Lesley Walker, Director of Cancer Information at Cancer Research UK, which owns the British Journal of Cancer, says: "It's been very difficult to separate out the effects of dietary fat and obesity and previous studies have been inconclusive.
"But by combining data from a wide range of studies using different methods and including a very large number of people, this research provides the strongest indication yet that dietary fat has an independent effect on the risk of breast cancer."
"Tying down the various dietary contributors to cancer is important, as it will allow us to give the best possible advice about how to avoid cancer. The effect of dietary fat looks quite small, but the results add weight to the importance of a healthy, balanced diet, low in saturated fat and containing plenty of fruit and vegetables."
- British Journal of Cancer89 (9)
- The Lancet362 (9379) pp.212-214