With Comments from Russell H. Greenfield, MD
Fat Intake and Breast Cancer Risk
Source: Cho E, et al. Premenopausal fat intake and risk of breast cancer. J Natl Cancer Inst 2003;95:1079-1085.
Goal: To determine whether there is a relationship between dietary fat intake and breast cancer risk in premenopausal women.
Design: Prospective cohort study (part of the Nurses’ Health Study [NHS] II) from 1991 to 1999.
Subjects: Women between the ages of 25-42 years who completed initial questionnaires in 1989, and then provided information biennially through 1999, including data on dietary habits.
Methods: The NHS II contains information from more than 100,000 female registered nurses in the United States, of whom more than 90,000 were premenopausal at initiation of the study. In 1989 they first responded to questions about medical history and lifestyle, and then regularly did so every other year from 1993 to 1999. Dietary intake was assessed in both 1991 and 1995 using a semi-quantitative food-frequency questionnaire containing more than 130 items, and cumulative results were averaged to approximate long-term intakes. Fat intake was calculated as the sum of contributions from all foods on the basis of food composition data. Breast cancer incidence was self-reported and confirmed by review of pathology reports.
Results: A total of 714 women were diagnosed with invasive breast carcinoma during the eight years of follow-up. In both age-adjusted and multivariable analyses, total fat intake was not associated with breast cancer risk. For the increasing quintiles of animal fat intake, however, relative risks (RR) were 1.00, 1.28, 1.36, 1.53, and 1.32. When animal fat intake was divided into deciles, the RR for breast cancer was 1.79 for individuals in the 10th decile relative to those in the first decile. The association between animal fat intake and increased risk of breast cancer was more prominent among women with estrogen or progesterone receptor-positive cancers than among women with hormone-negative cancers. Degree of vegetable fat intake was not associated with increased breast cancer risk.
Conclusion: Significant premenopausal intake of animal fat, mainly from red meat and high-fat dairy products, is associated with an increased risk of breast cancer.
Study strengths: Prospective nature; total number of subjects and level of compliance with protocol (93% follow-up rate); repeated measures; complex adjustments made for confounding factors.
Study weaknesses: Limited information on means of food preparation (i.e., were the meats blackened/charred on a barbecue?); inherent weaknesses with recall of food intake; limited duration of follow-up.
Of note: Some of the participants became postmenopausal during the follow-up period. When the analysis was restricted to only premenopausal women, a similar, albeit slightly weaker, association between animal fat intake and risk of breast cancer was found (RR for breast cancer in the highest quintile of animal fat intake compared with the lowest was 1.24); women with higher intakes of animal fat were more likely to use tobacco and alcohol products, to have a larger body mass index, and to have more than three children compared to women with lower intakes.
We knew that: Breast cancer kills approximately 40,000 people in the United States each year; national rates of breast cancer are strongly correlated with per capita total fat consumption; increased fat intake may elevate levels of circulating estrogen, though this has not been consistently borne out in human trials; etiologies of pre- and post-menopausal breast cancer may vary significantly; significant exposure to animal fats later in life may not have the same impact on breast cancer risk as exposure during early adulthood.
Clinical import: This is an excellent study that focuses on a population for whom prevention data are wanting—premenopausal women. Rates of invasive breast cancer among premenopausal women who ate a diet that was very high in animal (but not vegetable) fats were more than 30% higher than those for women who infrequently ingested animal fats. The results strongly suggest that it is less the total fat intake and more the specific type of fat regularly ingested that may place a woman at greater risk of breast cancer. It has long been known that high intake of saturated fats increases the risk for cardiovascular disease and colon cancer. These new data provide yet more compelling reasons to promote adherence to a diet high in fruits and vegetables, with only moderate intake of animal protein (yes, even ice cream!). The data do not address whether or not similar results would have occurred using primarily organic meat and dairy products.
What to do with this article: Make copies to hand out to your peers (and to the women you love).
Dr. Greenfield, Medical Director, Carolinas Integrative Health, Carolinas HealthCare System, Charlotte, NC, is Executive Editor of Alternative Medicine Alert.