Diet and breast cancer in causation and therapy.

The major macronutrient associated with increased breast cancer risk is dietary fat. Evidence for this association is based on epidemiologic, clinical, and laboratory animal studies. In addition, there is suggestive epidemiologic evidence that differences in postmastectomy survival rates in Japan and the United States may be attributable to differences in dietary fat intake. The importance of the type of fat consumed, as well as its amount, has emerged as an issue of major importance. Some oils, including those rich in monounsaturates, medium chain fatty acids, or omega-3 (n-3) fatty acids appear to lack tumor-promoting effects despite their presence in the diet at high levels. Possible mechanisms by which dietary fat may exert its effects could be either direct or indirect. Direct mechanisms involve dietary modification of membrane structure and function; indirect mechanisms involve alterations in the endocrine system, and/or the metabolism of essential fatty acids to biologically active eicosanoids such as prostaglandins, and suppression of immune responses. Dietary guidelines and dietary intervention trials for the primary and secondary prevention of breast cancer are discussed.