Effect of Dietary Fat on Risk for Breast Cancer Is Modest

March 27, 2007 — Another study has suggested a link between higher intake of dietary fat and a higher risk for breast cancer. However, the association is "modest," experts point out, and they suggest that prevention advice should focus on reducing body fat through diet and exercise, rather than on reducing fat intake. The latest results come from the National Institutes of Health (NIH)–AARP (formerly the American Association of Retired Persons) Diet and Health Study and are reported in the March 21 issue of the Journal of the National Cancer Institute.

This study followed up 188,736 postmenopausal women for an average of 4.4 years and found that the rate of invasive breast cancer in women was 11% to 22% higher in women who had a high fat intake (90 g/day or 40% calories from fat) than in those who had a low fat intake (24.2 g/day or 20% calories from fat).

The authors, led by Anne C. M. Thiébaut, PhD, at the National Cancer Institute, made a correction for measurement error in fat and energy intake, which strengthened the observed association. For a doubling in total fat intake, the corrected hazard ratio (HR) was 1.32, with a 95% confidence interval (CI) of 1.11 to 1.58.

"Even with this correction for measurement error, this study provides further evidence that the association between total fat intake and the risk of breast cancer among postmenopausal women is likely to be modest," comment Stephanie A. Smith-Warner, PhD, and Meir J. Stampfer, MD, PhD, from the Harvard School of Public Health, Boston, in an accompanying editorial.

The results of the NIH-AARP Diet and Health Study are similar to the summary relative risk estimate from a meta-analysis of 31 case-control studies and 14 cohort studies that was published a few years ago (Br J Cancer. 2003;89;1672-1685), the editorialists comment. This meta-analysis found that the overall summary relative risk estimate from all of the studies for the highest vs the lowest fat intake was 1.13 (95% CI, 1.03 - 1.25).

More recently, the Women's Health Initiative Dietary Modification Trial reported a marginally statistically significant 9% reduction in breast cancer incidence among women in a low-fat intake group compared with controls (HR, 0.91; 95% CI, 0.83 - 1.01). However, this result cannot be attributed solely to a decrease in fat intake, the editorialists comment, as the women in the intervention group also lowered their energy intake and body weight and increased their intake of fruit, vegetables, fiber, and folates. Other commentators have suggested that the reduction in breast cancer incidence seen in this study was probably due to the notable reduction in body weight that these women experienced.

"On the basis of the main findings from the NIH-AARP Diet and Health Study and other studies described above, it appears that dietary fat intake during postmenopausal years has little, if any, impact on breast cancer risk," the editorialists conclude. There are hints that a higher intake of fat may increase the risk for breast cancer in specific subgroups, such as younger women, or those who are using hormone replacement therapy. It may be that dietary fat has more influence on the risk for breast cancer when it occurs in the context of an estrogen-rich environment, they comment. This potential interaction is "of interest" and is worth investigating further, as are the potentially different effects of specific subtypes of fat (ie, saturated vs unsaturated, as well as fats in red meat, dairy products, etc), they add.

"The modest associations that have been observed for dietary fat and breast cancer risk in observational studies and clinical trials stand in sharp contrast to the robust evidence for a strong link between adiposity and the risk of postmenopausal breast cancer," the editorialists comment. "Thus from a prevention perspective, interventions to control the amount of body fat (eg, promotion of exercise and caloric restraint) are likely to have a greater impact on breast cancer incidence than a reduction in fat intake."

The authors have disclosed no relevant financial relationships.

J Natl Cancer Inst. 2007;99:418-419, 451-462.

Source: http://www.medscape.com/viewarticle/554148?src=mp