Journal Name:
Nutr. Cancer
Article Title:
Dietary fat, cooking fat, and breast cancer risk in a multiethnic population.
Date Written:
2008
Volume:
60
Number:
4
Page:
492
Author(s):
Wang, J.; John, E.M.; Horn-Ross, P.L.; Ingles, S.A.
Article:
Diet, especially dietary fat, has been widely investigated as a potential risk factor for breast cancer. Extensive evidence supports the hypothesis that fat contributes to breast cancer initiation and promotion as do large ecologic studies and international comparisons. Both total fat and the major fat subtypes, including saturated fat, monounsaturated fat, and polyunsaturated fat, have been linked to increased risk of postmenopausal breast cancer. However, different effects have been reported for different types of fatty acids in several meta-analysis of animal studies, with n-6 polyunsaturated fats having a strong and saturated fats having a weaker promoting effect in mammary carcinogenesis, whereas monounsaturated fats have no statistically significant effects.
The objective of the present study was to examine the association between dietary fat intake, cooking fat usage, and breast cancer risk in a population-based, multiethnic, case-control study conducted in the San Francisco Bay area. Intake of total fat and types of fat were assessed with a food frequency questionnaire among 1,703 breast cancer cases diagnosed between 1995 and 1999 and 2,045 controls. In addition, preferred use of fat for cooking was assessed.
High fat intake was associated with increased risk of breast cancer (highest vs. lowest quartile, adjusted OR = 1.35). A positive association was found for oleic acid (OR = 1.55) but not for linoleic acid or saturated fat. Risk was increased for women cooking with hydrogenated fats (OR = 1.58) or vegetable/corn oil (rich in linoleic acid) compared to women using olive oil or canola oil (rich in oleic acid). Two complementary approaches were used to assess the effects of different types of dietary fats on breast cancer risk. To capture the multiple food sources that contribute to each dietary fat subtypes, the intake of specific fat components was assessed from a food frequency questionnaire (FFQ). In addition, preferred use of cooking fat was examined to assess the effects of naturally occurring complex mixtures of different fatty acids on breast cancer risk. Whites, African Americans, and Latinas women were included.
The results were inconsistent as by estimating fat intake by FFQ, oleic acid was found to be associated with increased risk, whereas no associations were found for linoleic acid and saturated fat intake. In contrast, when analyzing cooking fat usage, increased risk was associated with using hydrogenated fat or vegetable/ corn oil (rich in n-6 polyunsaturated fat). Women using olive/canola oil were at lower risk, similar to those who used no fats for cooking. This apparent discrepancy—that monounsaturated fat as measured by FFQ increases breast cancer risk, yet edible oils such as olive or canola oil are associated with lower risk than fats rich in n-6 polyunsaturated fats and hydrogenated fats—is reflected in the epidemiologic literature.
Among all types of cooking fat, hydrogenated fat conferred the highest risk of breast cancer. The effects of trans fat on mammary carcinogenesis have been rarely investigated, and the mechanisms are currently not clear. Alternatively, the observed protective effect of cooking fats high in monounsaturated fats may be related to other attributes of the fat source in addition to its fatty acid composition such as vitamins, flavonoids, and phenolic compounds found in olive oil and the ALA found at a relatively high level (>10%) in canola oil.
A positive association between total or monounsaturated fat and breast cancer risk was observed only among Whites and Latinas but not among African Americans. The inconsistency may reflect important confounding issues that have not been identified or that were not easy to adjust for. For example, 10% of BMI data came from self-report, which might have caused some misclassification and resulted in residual confounding. Although a similar association between cooking fats and breast cancer risk was found in all three racial/ethnic groups, it is also possible that some unmeasured components in diet, such as trans fats, are responsible for the inconsistent findings for oleic acid intake measured by the FFQ.
These findings support the recommendations regarding the adoption of a low-fat diet to reduce breast cancer risk. It is also speculated that monounsaturated trans fats may have driven the discrepant associations between types of fat and breast cancer.
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