Dietary fat and breast cancer: case-control and cohort studies.

An increased risk of breast cancer in relation to a high-fat diet has been reported in several case-control studies and one cohort study conducted in different parts of the world. Most of these studies provide data on the consumption of food groups high in animal fats, e.g., meats and dairy products. Studies reporting on the amount of fat constituents consumed, adjusted or unadjusted for total caloric intake, more frequently have shown no positive association. The latter studies are not all limited to countries such as the United States with an overall high dietary fat intake; one was reported from Japan where the traditional low-fat diet is giving way to more Western-style foods, resulting in greater dietary heterogeneity for the population. The hypothesis that dietary fat causes breast cancer has been seriously weakened by the recent negative reports from two U.S. cohort studies, employing well-recognized dietary assessment strategies and multivariable analytic methods. Still, the possibility exists that specific fat constituents either naturally present or produced during the food preparation process, or fats in the presence (or absence) of other foodstuffs could alter breast cancer risk. Different kinds of studies providing information on the biochemistry and biology of fats consumed by humans would help to give focus to future epidemiological studies.