March 20, 2007 -- There is more evidence linking high-fat diets to a modest increase in breast cancer risk among older women. But all agree that more study is needed to prove an association once and for all.
In the largest study ever to address the issue, researchers from the National Cancer Institute (NCI) asked 188,736 postmenopausal women about the foods they ate and then followed the women for an average of 4.4 years.
They found that women whose diets included the most fat were 15% more likely to develop breast cancer than women who ate the least fat. The association was seen both in women who were overweight and those of normal weight.
"Fifteen percent is modest, but it could have a huge impact because breast cancer is so common," researcher Anne C. M. Thiebaut, PhD, tells WebMD. "This is certainly an issue that deserves further investigation."
Many Studies, Little Consensus
Researchers have been studying the question for decades, but there is still little consensus on whether fat intake influences breast cancer risk. In a recent analysis of 14 studies, women who ate the most fat had a 13% higher risk of breast cancer compared with women who ate the least.
Eating a low-fat diet was found to reduce breast cancer risk by 9% in a recently reported Women's Health Initiative intervention trial. This association was considered marginally statistically significant, meaning it was not likely due to chance.
In the newly published study, Thiebaut and NCI colleagues followed women between the ages of 50 and 71 participating in the larger National Institutes of Health-AARP Diet and Health Study.
The participants completed a detailed survey to determine their dietary habits at study entry. During the 4.4-year average follow-up, 3,501 of the women developed breast cancer.
Compared with women whose diets averaged 20% of calories from fat, women who derived roughly 40% of their calories from fat sources had a 15% increased risk for developing breast cancer.
The types of fats the women ate appeared to have little bearing on risk. No additional increase in risk was seen among women who ate large amounts of saturated fats, as has been suggested in several other studies.
Thiebaut and colleagues conclude that their findings "should contribute to the ongoing debate about the association between dietary fat and the risk of breast cancer."
The study appears in the March 21 issue of the Journal of the National Cancer Institute.
Focus on Weight Loss
The NCI findings seem to support the idea that dietary fat increases breast cancer risk in postmenopausal women, but they also suggest, as other studies have, that the impact is modest at best.
In an accompanying editorial, Stephanie Smith-Warner, PhD, and Meir Stampfer, MD, of Boston's Harvard School of Public Health, write that there is much more evidence linking obesity to breast cancer in older women.
They suggest that public health messages should focus on getting women to lose extra weight rather than getting them to restrict the fat in their diets.
"From a [breast cancer] prevention perspective, interventions to control the amount of body fat are likely to have a greater impact on breast cancer incidence than a reduction in fat intake," they write.