Dietary Fiber and Breast Cancer Risk

Abstract

Globally, breast cancer is the second most common cancer among women; in developed countries, it is the most common cancer (1). The rise in breast cancer incidence in developing regions (1,2), which typically have lower rates of breast cancer compared to industrialized nations, may be partly related to a trend towards more Westernized diets, i.e., high in fat and low in dietary fiber (3). The link between dietary factors and breast cancer risk was first apparent in ecological or correlation studies. International comparisons have found positive correlations between estimated per capita fat consumption in different countries and breast cancer incidence or mortality rates (4–9). Few studies have looked at international differences in dietary fiber consumption or intake of fiber-rich foods and breast cancer risk, observing both high inverse correlations (7,10,11) or no association (8). Other studies looking at general carbohydrate intake, which may include dietary fiber, starch, and sugars, have found moderate inverse correlations with breast cancer incidence or mortality (5,6). Migrant studies have provided further evidence that the correlations observed in the ecological studies were due to environmental rather than genetic factors. Migrants from regions with low breast cancer incidence and mortality rates such as Japan, China, and Latin America acquire the higher rates characteristic of their new location (i.e., the United States and Western European countries) after one or two generations (12). This change in breast cancer risk observed in subsequent generations has been attributed to changes in dietary habits. Using correlation and migrant studies as a basis, Doll and Peto (13) have estimated that 50% of breast cancer deaths may be attributable to diet. However, the role of specific dietary components in modulating breast cancer risk is not clear. Of all the nutrients, dietary fat has been the most extensively studied in its relationship to breast cancer. Although most international correlation studies have found strong, positive associations between dietary fat intake and breast cancer (14), only 3 out of 25 case-control studies have found a significant increase in breast cancer risk (15). On the other hand, metaanalyses of case-control studies have significant increases in risk with total fat intake (16,17), particularly in postmenopausal women (16). Of the nine cohort studies examining the relation-