Breast cancer considerations to assist the practitioner in clinical recommendations - Women's Health Update

Townsend Letter for Doctors and Patients,  June, 2002  by Tori Hudson

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Practitioners and patients confront several poignant issues in the prevention, diagnosis and management of breast cancer. What is the role of dietary fat in our risk of breast cancer? Are screening mammograms beneficial or not? Is soy safe in the prevention and treatment of postmenopausal women with or without breast cancer? Does HRT cause or increase the risk of breast cancer? I've written on most of these topics in the recent past and I've decided to reproduce and augment those writings and collect them in this article in the hopes of facilitating our approach to this all important topic.

Nutrition

Breast Health, Dietary Fat and Essential Fatty Acids

Dietary fat has been the center of much controversy in regard to its impact on breast cancer. A review of some of the pertinent findings will be helpful. About 30 years ago, the fat intake of many countries was plotted on a graph against breast cancer rates. (1) With few exceptions, the more fat individuals in that society consumed, the higher the risk of breast cancer. Ten out of ten international studies looking at large differences in fat intake from one country to another continued to confirm this relationship between higher dietary fat levels and higher rates of breast cancer. By and large, the women who live in cultures with the lowest fat diet like Japan and Thailand, have the lowest rates of breast cancer. Women in the Middle East who have medium rates of breast cancer have medium amounts of fat in the diet. Women in Europe and North America with the highest intake of dietary fat have the highest rates of breast cancer. However, in 1992, the Nurses' Health Study group found no such link.' There have been many critiques of this study that have pointed out the inaccuracy of the measurements used and results obtained but perhaps the most compelling at the time was that of the five categories of dietary fat that were analyzed. Its most glaring deficiency was that the group with the lowest amount of fat was still only slightly lower than 29%. This is notably higher than the 20% many researchers believe to be the beginning of where women would receive the protection. In March of 1999, a followup analysis of 88,795 women extended the Nurses' Health Study for another 6 years and more than 1500 cases. (3) This extended study is now considered large enough and long enough to assess the effect of less than 20% fat intake as well as examining risk of different types of fat. Surprising to many, they saw no increased risk of breast cancer with increased intake of animal fat, polyunsaturated fat, saturated fat, or transunsaturated fat. They also found no evidence of decreased risk of breast cancer with increased intake of vegetable fat or monounsaturated fats. Also contrary to the. predominant hypothesis, they observed an increased risk of breast cancer associated with omega-3 fat from fish. The strength of this second report is that the analysis was prospective, and included more cases with longer follow-up than the previously studied report. However, the capacity to examine breast cancer risk at the extremes of fat intake is limited by the small proportion of women in those groups and a greater probability of misclassification of dietary intake in these categories.

Numerous other studies have pointed out the protective benefits of olive oil and fish fat. A study published in the Journal of the National Cancer Institute in 1995 demonstrated that increased olive oil consumption was associated with a lowered risk of breast cancer in Greek women by 25%. (4) Two case-control studies, one in Spain and another in Italy, as well as the Greek study are reasonably large, properly analyzed studies of monounsaturated fat and breast cancer. The Spanish study and the Greek study have similar results, suggesting a protective effect of olive oil. The Italian study found a strong positive association between saturated fat intake and breast cancer risk, but no association with monounsaturated fat intake. Another study in France showed a protective effect between breast cancer and the consumption of olive oil, although it was not considered statistically significant. A recent survey was completed in Sweden studying 61,471 women from 1987 to 1990. (5) They reported that monounsaturated fa t reduced the risk of breast cancer by 45 percent. They credited the effects of canola oil and olive oil, the oils highest in oleic acid. To achieve optimum protection, 2 tablespoons per day is recommended.

It is still thought by most nutrition experts that one of the best ways to reduce the risk of breast cancer is to consume more omega-3 fatty acids. The protective effect of omega-3 fatty acids was first observed in Greenland Eskimo women who seemed to have a strikingly low rate of breast cancer. These women have a diet that is probably the highest in omega 3 fats of any women to date. Laboratory, animal and epidemiological studies almost universally show reductions in breast cancer associated with high omega 3 fish oils. Fats containing high amounts of omega 3 polyunsaturated fats have been reported to have a suppressive effect on tumor growth in female rats as well as other animal models that have been studied. Fish that are generally available and contain high amounts of omega 3 oils include salmon, tuna, halibut, mackerel, sardines and herring. The use of fish oil supplements can also be used to supply the all important omega-3 oils.