As long ago as 1982, the National Research Council published a report called Diet, Nutrition, and Cancer, showing the evidence already available linking specific dietary factors to cancer of the breast and other organs.
Asian countries, such as Japan, have low rates of breast cancer, while Western countries have cancer rates that are many times higher. However, when Japanese girls are raised on westernized diets, their rate of breast cancer increases dramatically.
The traditional Japanese diet is much lower in fat, especially animal fat, than the typical Western diet. In the late 1940s, when breast cancer was particularly rare, less than 10 percent of the calories in the Japanese diet came from fat. The American diet, of course, is centered on animal products, which tend to be high in fat and low in other important nutrients. The fat content of the average American diet is in the range of 37 to 40 percent of calories.
Countries with a higher intake of fat, especially animal fat, have a higher incidence of breast cancer. Even within Japan, affluent women who eat meat daily have an 8.5 times higher risk of breast cancer than poorer women who rarely or never eat meat. The Surgeon General’s Report on Nutrition and Health stated: “Indeed, a comparison of populations indicates that death rates for cancers of the breast, colon, and prostate are directly proportional to estimated dietary fat intakes.”
Surviving Breast Cancer
Not all cancers are the same. Some have a relatively good prognosis, and others have a very poor prognosis. For example, a tumor that is small and has not spread to the lymph nodes or other organs is less dangerous than a tumor that is larger and has already spread. (Lymph nodes are pea-sized collections of cells near the breast and other organs which are important to immune function.) Hospital laboratories also determine whether a breast tumor has receptors for estrogen or progesterone hormones. If it does, the tumor is slightly less aggressive than if it lacks receptors.
These prognostic factors are not due to chance alone. Thirty years ago, Ernst Wynder of the American Health Foundation in New York observed that, aside from the fact that Japanese women are much less likely than American women to get breast cancer, when Japanese women do get the disease, they tend to survive longer. Their improved survival is independent of age, tumor size, estrogen receptor status, the extent of spread to lymph nodes, and the microscopic appearance of the cancer cells. And it is not that Japanese women have better health care, because the same pattern has been observed in Hawaii and California, where Japanese women live nearby other ethnic groups, and have essentially the same health care system.
Researchers have begun to look at whether diet plays a role in survival. It does. Our old enemy, fat in foods, rears its ugly head once again. The more fat there is in the diet, the shorter a cancer patient survives. In a Canadian research study, women with cancer were more likely to have lymph node involvement if they had a higher fat intake. This effect was found only for saturated fat and only for post-menopausal women. Fat seems to have a measurable effect when cancer has spread to other parts of the body, and little or no effect when the disease is localized.
Researchers in Buffalo, New York, calculated what they believe to be the degree of risk posed by fat in the diet: for a woman with metastatic breast cancer (cancer which has already spread at the time of diagnosis), her risk of dying from the disease at any point in time increases 40 percent for every 1,000 grams of fat consumed monthly. In order to understand what this means, compare three different diets, each of which contains 1,200 calories per day:
- On a low-fat, vegetarian diet , about 10 percent of calories come from fat. This type of diet contributes about 13 grams of fat per day, or 400 grams per month.
- On a typical American diet , 37 percent of calories come from fat. This means about 49 grams of fat per day, or 1,380 grams per month.
- On a diet with more fat than average , say 50 percent of calories, fat intake would be 67 grams per day, or 2,000 grams per month.
If the researchers’ finding holds, the typical American diet would lead to about a 40 percent higher risk of dying of breast cancer at any given point, compared to the low-fat, vegetarian diet, and the high-fat diet would lead to a more than 60 percent increase in risk of dying. These figures do not mean that a woman’s risk of dying is 40 percent or 60 percent. They mean that the risk is 40 percent or 60 percent higher than it would otherwise have been, assuming the individual is comparable to those studied.
Other parts of the diet play important roles. Diets that are high in fiber, carbohydrate, and vitamin A seem to help the prognosis, while alcohol slightly worsens it. Patients who have more estrogen receptors on their tumors (which indicates a better prognosis) tend to be those who had consumed more vitamin A. (Beta-carotene becomes vitamin A in the body.) For reasons that are not entirely clear, vegetables and fruits, and the vitamins they contain, help keep the cells of the body in better working order—one sign of which, for breast cells, is the presence of estrogen receptors. So vegetables and fruits are not only important in helping to prevent cancer, but also in improving survival for those who have cancer.
Higher body weight increases the risk of dying of breast cancer. Among postmenopausal women with breast cancer, slimmer women tend to have less lymph node involvement. Heavier women have more lymph node involvement, higher rates of recurrence, and poorer survival.