The large international variations in risk for breast cancer prompted interest in possible dietary causes of breast cancer [77].

Several investigators examined particular international and intercultural dietary differences and proposed that diets that are low in fat and high in fruits, vegetables, fiber, and complex carbohydrates might lower risk for breast cancer [78, 79].

Although prospective observational studies in humans have generally not supported this, several experimental studies have provided support for an association between certain dietary patterns and a lower risk for breast cancer [80].

Animal experimental studies have shown a higher rate of development (via promotion of tumorigenesis) of mammary tumors with greater polyunsaturated or saturated fats intake [77].

However, it is not clear if the dietary fat per se, or the greater energy intake, was responsible for the greater development of mammary tumors in those studies.

Human experimental evidence is available on the effects of low-fat and high-fiber diets on some breast cancer biomarkers.

The effect of a low-fat, high vegetable and fruit diet on mammographic density, a breast cancer biomarker, was tested in a randomized clinical trial in 817 women [81].

Women randomized to the diet arm experienced a 6.1% decrease in mammographic density over 2 years compared with a 2.1% decrease in controls (p = 0.01).

Several small clinical trials and other interventional studies have shown a reduction in circulating estrogen levels, as described in a recent review [82], although there is still a question regarding whether it was the diet per se, or the weight loss resulting from the dietary changes, that caused the reduction in hormones [83].

Definitive evidence of the effect of a low-fat dietary pattern on risk of breast cancer awaits the results of the WHI Dietary Modification clinical trial [57].

The trial includes over 48,000 postmenopausal women aged 50–79 from diverse geographic, cultural, race, and ethnic groups around the U.S. The WHI dietary goal is 20% of calories from fat, five servings of fruits/vegetables per day, and six servings of grains per day.

The trial was begun in 1993 and will continue until 2005.

While intake of dietary fat per se has not been established as associated with risk for breast cancer, increased dietary fat typically increases caloric intake. This results in overweight and obesity, which are risk factors for breast cancer.

Therefore, prudent advice for women wanting to avoid lifetime weight gain, overweight, and obesity, would be to follow a diet that is low in dietary fat.

Vegetables and Fruits

Early epidemiologic studies suggested a role for a high intake of vegetables and fruits in a low risk for breast cancer [77]. A combined analysis of eight cohort studies representing 351,825 women (7,377 breast cancer cases), however, found no association between intake of vegetables and fruits and risk of breast cancer [84].

Soy, Isoflavones, and Lignans

Epidemiologic data suggest that consumption of soy products is associated with a lower risk for breast cancer [82, 85]. Many soy-based foods are available in the U.S., including tofu, soy milk, soy cheeses, frozen "yogurt," breakfast shakes, soy nuts, meat substitutes, and salad dressings [86].

Recent evidence suggests that one component of soy, genistein, may promote the growth of some estrogen-sensitive tumors and reduce the efficacy of tamoxifen, which emphasizes the need for additional studies to determine whether soy is safe for women with breast cancer or who are at a greater risk for breast cancer [87, 88].

Phytoestrogens can act as weak estrogens and as estrogen antagonists, depending on the hormonal milieu of the host. Thus, high phytoestrogen intake can compete with endogenous estrogens in premenopausal women and reduce overall estrogen exposure to target tissue.

Conversely, phytoestrogens can increase estrogen activities in women with low endogenous levels of estrogens, for example, postmenopausal women.

These findings have been confirmed in animal experiments and in a small number of human experimental studies [77, 89–91].

Meat and Dairy

Some studies have pointed to a high intake of meats as a risk factor for breast cancer, but other studies have not supported this [77].

Part of the discrepancy in findings may be the different levels of carcinogens and mutagens included in meat in different areas around the world.

Intake of dairy foods has not been found to be associated with risk for breast cancer, and a recent report from a large cohort study suggests a lower risk with a greater intake of low-fat dairy products in premenopausal women [92].

In that study, the multivariate RR comparing the >1 serving/day with the 3 servings/month intake categories were 0.68 (95% CI = 0.55–0.86) for low-fat dairy foods and 0.72 (95% CI = 0.56–0.91) for skim/low-fat milk.

Dairy calcium (>800 mg/day versus 200 mg/day; RR = 0.69, 95% CI = 0.48–0.98) and vitamin D (>500 IU/day versus 150 IU/day; RR = 0.72, 95% CI = 0.55–0.94) intakes were also inversely associated with premenopausal breast cancer risk [92].

The fat content of dairy products may promote a greater risk for breast cancer through a greater energy intake in the diet. On the other hand, the high calcium and vitamin D contents of many dairy products may be protective against breast cancer [92].

Vitamins and Minerals

Several epidemiologic studies have investigated the association between dietary and supplement intakes of various vitamins and minerals and the risk of breast cancer.

Specific micronutrients that have been associated with a lower risk include carotenoids, folate, calcium, vitamin D, lycopene, and vitamin C [77, 93–95]. Those studies have had mixed results, however, and because they have all been observational, are not conclusive.

New analyses of prospective studies suggest that women with low folate intakes and greater alcohol intakes have a greater risk for breast cancer than nondrinkers with normal folate intakes [96, 97].

In the Nurses’ Health Study cohort, among women who consumed at least 15 g/day of alcohol, the risk of breast cancer was highest among those with low folate intakes [97]. For a total folate intake of at least 600 ΅g/day compared with 150–299 ΅g/day, the multivariate RR was 0.55 (95% CI = 0.39–0.76; trend p = 0.001).

Ann's NOTE: We have corresponded with many of the authors of studies looking at intake of fruits and vegetables. What we found was so interesting. Quite often the comparison of the high amount of fruits and vegetables would be one to two per week and the low one per month. This is nowhere near the National Cancer Institute's suggested '9 a Day'.

It is our contention that fruit and vegetable intake as a risk reduction for cancer has not yet been properly evaluated.

Remember we are NOT Doctors and have NO medical training.

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