EVIDENCE-BASED ANSWER
No. Studies show no evidence that reducing dietary fat decreases a woman’s risk of developing postmenopausal breast cancer within the subsequent 14 years (strength of recommendation [SOR]: B, based on large heterogeneous prospective cohort studies and appropriate meta-analyses of these studies). Overall, evidence is insufficient to recommend for or against reduction in dietary fat to reduce risk of breast cancer for women, although recommendations for prudent fat intake may be justified on other grounds.
Clinical commentary
Losing weight is still a good strategy
Kathryn Kolasa, PhD, RD, LDN
East Carolina University, Greenville, NC
Women at risk for breast cancer—and cancer survivors—want to know about lifestyle changes that can reduce their risks for cancer or recurrence. There is growing evidence that obesity plays a role in cancer development and promotion.
A low-fat diet has been demonstrated as a successful strategy for weight loss. However, for most women, making these changes can be difficult without extensive instruction, support, and motivation. Limiting sweetened beverages, increasing consumption of fruits and vegetables, and limiting fat intake are 3 strategies women can use to achieve a healthy weight. If this turns out to reduce their risk of breast cancer, so much the better!
Evidence summary
Our Medline search retrieved 1114 English-language studies published from 1960 through October 2006. We limited this set to randomized controlled trials and cohort studies, leaving 212 articles. We then excluded articles that had small sample sizes, did not follow subjects for at least 5 years, did not include original data, included men, did not give prevalence or incidence rate of breast cancer in the subjects, or did not discuss diet assessment tools. Of the remaining articles, we selected the 11 best studies to include in the review.
Early studies evaluating national average dietary fat intake and breast cancer incidence rates showed an almost linear relationship between increased dietary fat and increased breast cancer incidence.1 However, increased fat intake occurs primarily in industrialized nations, providing multiple possible confounders for increased rates of breast cancer, such as pollutants and increased consumption of preservatives, pesticides, and other chemicals.
Case-control studies have shown some minimally increased risk related to dietary fat consumption, but there is concern about recall bias in these studies.2 Since the late 1970s, 7 large, well-designed prospective cohort studies have examined the possible relationship between dietary fat and breast cancer.1 The findings have been somewhat contradictory, with some studies showing statistically significant associations toward increased risk with higher fat intake.3-5