Good choices
•Folic acid (folate) for women who consume alcohol

Risky choices
•Excess calories
•High soy intake (uncertain)

Despite years of research on the topic, the connection between food and breast cancer remains unclear. Regarding fruits and vegetables, for example, studies have revealed little protective effect. Most experts now think that hormones have a much greater effect on breast cancer risk than diet does.

For example, in a major analysis of several studies of large groups of women, those who ate the most fruits and vegetables had about the same risk of developing breast cancer as those who ate the least. More recently, a diet high in vegetables, fruit, and fiber and low in fat didn’t prevent further breast cancer or death in early-stage breast cancer survivors over a seven-year follow-up period, reported a 2007 study in JAMA.

Hormones. The key to breast cancer seems to be factors that raise a woman’s exposure to hormones, particularly estrogen, over a lifetime. Early age at first menstruation, less time spent breast-feeding, later age at first pregnancy, use of postmenopausal hormones, weight gain after menopause, and sedentary living all seem to raise the risk of developing breast cancer. Taller women also seem to have higher risk of developing breast cancer. But height is not the cause of this increased risk. Instead, height is an indicator of other factors, including hormonal factors, that promote growth in childhood.

Dietary fat. One of the most-studied questions in the diet–breast cancer connection is the role of dietary fat. Scientists became interested in this question when international studies showed that women in countries where fat consumption was low had low rates of breast cancer. Not only that, but when women migrated to the United States, where fat consumption is high, breast cancer rates rose both for the women who migrated and for their daughters.

In 1989, the National Academy of Sciences recommended cutting fat from the diet as one of the best ways to prevent breast cancer, as well as colorectal cancer and prostate cancer. Later studies didn’t confirm the idea that a high-fat diet contributes to breast cancer, and the connection between diet and breast cancer appeared weak. In particular, the large Nurses’ Health Study hasn’t found a link between fat consumption and breast cancer. Then, in 2006, authors of the randomized Women’s Health Initiative dietary modification study suggested that a slight trend toward lower breast cancer rates in women on a low-fat diet might become more solid if the women were followed longer. However, women on low-fat diets lost about 5 pounds, so the lower breast cancer rates may have been the result of losing weight rather than eating less fat. The same year, another randomized trial in women treated for breast cancer, the Women’s Intervention Nutrition Study, credited modest weight loss (6 pounds), not lower dietary fat, with a small reduced risk of recurrence.

Calories and body fat. Body fat, unlike fat in the food you eat, seems to have a stronger link to breast cancer. Studies of animals as well as humans consistently show that eating too many calories increases the risk of breast cancer and that reducing calories seems to lower breast cancer risk. Animal research suggests that calorie restriction might slow down cell division, a hallmark of cancer, and inhibit tumor growth. In laboratory animals, cutting daily calories by 30% reduced mammary cancer rates by as much as 80%.

General fatness and belly fat also are probable risk factors for postmenopausal breast cancer, but not premenopausal breast cancer. Your risk of postmenopausal breast cancer increases by about 10% with every 11 pounds you tack on to your frame. Researchers think this occurs because fat cells contain the enzyme aromatase, which converts other hormones into estrogen, a known promoter of breast cancer. In one large study, postmenopausal women who gained the most weight were more than twice as likely to develop breast cancer compared with women who gained no weight or lost weight.

Exercise. Similarly, exercise seems to be more important in postmenopausal women in lowering the risk of breast cancer than in younger women, with lowered risk proportional to the hours of activity every week.

How does all this information translate to practical, daily eating patterns that might help reduce breast cancer risk? Aim for a BMI in the range of 19 to 24. If you need to lose weight, strive to burn more calories than you consume by eating less and exercising more. That basic weight-loss recipe for success was underscored in a 2009 New England Journal of Medicine study in which participants with a BMI between 25 and 40 were put on diets with varying levels of fat, protein, and carbohydrates. They also burned 750 more calories than they consumed each day. After two years, everyone lost similar amounts of weight, which solidified the fact that a diet with fewer calories — no matter whether it’s higher in protein, fat, or carbohydrates — leads to weight loss.

Alcohol and folic acid. Several large studies showed that having two drinks a day increased a woman’s risk of developing breast cancer by 20% to 25%. A larger analysis of seven major population studies found that drinking one glass of any kind of alcohol per day increased a women’s risk of breast cancer by about 9%. In weighing the evidence, the 2007 global report from the World Cancer Research Fund and the American Institute for Cancer Research cited alcoholic drinks as a cause of breast cancer (see “Preventing cancer: Global report recommendations”). A possible explanation for the alcohol–breast cancer connection is that moderate alcohol consumption boosts the body’s levels of estrogen, which can promote breast cancer. Interestingly, having a diet rich in folic acid may cancel out this risk.

The Nurses’ Health Study and other studies have shown that women who consume more than one drink a day but also get 600 mcg or more of folic acid don’t have a higher risk of breast cancer than women who drink less. You can lower your risk of breast cancer by holding your alcohol intake to no more than one drink a day or less and getting 600 mcg of folic acid a day. You can get folic acid from a multivitamin, as well as from lentils and other legumes and fortified breakfast cereals, flour, pasta, rice, and other grain products. Most processed cold cereals are fortified with 100 mcg of folic acid, and most multivitamins provide 400 mcg.

Preventing cancer: Global report recommendations

In November 2007, the World Cancer Research Fund and the American Institute for Cancer Research released the second global report on Food, Nutrition, Physical Activity, and the Prevention of Cancer. For five years, a 21-scientist expert panel evaluated the best evidence conducted by dozens of scientists in 30 countries and then debated the meaning of the evidence to arrive at public health recommendations.

Many recommendations in the report also apply to dietary causes of cardiovascular disease. The notable exception is alcohol: for preventing cancers, the best level of consumption is zero; for cardiovascular disease, it may be one to two drinks a day. The authors also emphasize the importance of avoiding exposure to tobacco smoke.

Recommendations include the following:

Body fatness. Avoid weight gain and try to be as lean as possible without becoming underweight.

Physical activity. Be physically active for at least 30 minutes every day.

Avoid sugary drinks. Limit consumption of calorie-dense foods such as sodas and other high-calorie, low-nutrient foods.

Plant foods. Eat more of a variety of vegetables, fruits, whole grains, and legumes such as beans.

Animal foods. Limit consumption of red and processed meats.

Alcoholic drinks. If you drink, limit alcoholic beverages to no more than two drinks a day for men and one drink a day for women.

Salt. Limit your consumption of salty foods and foods processed with sodium.

Dietary supplements. Don’t rely on supplements to protect against cancer.

Special recommendation for breast-feeding women: Mothers should breast-feed exclusively for up to six months and then add other liquids and foods to their baby’s diet.

Special recommendation for cancer survivors: After treatment, cancer survivors should follow the recommendations for cancer prevention.

Source: Food, Nutrition, Physical Activity, and the Prevention of Cancer: A Global Perspective, World Cancer Research Fund and the American Institute for Cancer Research,, November 2007.