Diet and Breast Cancer

by Michelle Busch, RD, LD

What dietary factors can influence a woman’s risk of developing breast cancer or surviving that diagnosis? Much media attention has been directed at examining how diet can affect cancer risk. Some of the information you read may seem to be contradictory. One study says that fat increases breast cancer risk and another says it decreases risk. It is important to look at the big picture when interpreting research. What does the preponderance of the evidence suggest? One or two studies will not provide adequate information upon which to base lifestyle decisions on.

Information also evolves over time as we learn more. That fat controversy mentioned earlier has gone from fat as the culprit to total caloric intake. Total caloric intake in some studies was a stronger determinant of breast cancer than dietary fat. Obesity and gaining weight during adulthood are also risk factors. Research is continuing in this area to determine how different types of fat may affect breast cancer risk. At this time, the best recommendation is to try to achieve and maintain a healthy weight and to keep total fat intake to around 30% of total calories. Choose “heart healthy” oils such as olive and canola oil. These fats may also affect cancer risk, not just your heart.

Alcohol consumption is another known risk factor for breast cancer. The risk increases as the amount of alcohol consumed increases. There is a weak association between alcohol consumption and breast cancer in women who drink one alcoholic beverage a day. Drinking more, about two to five drinks per day, may be associated with a rate of breast cancer that is about 40% higher than the rate for nondrinkers. And wine is not any better than beer or hard liquor. The 1996 Guidelines on Diet Nutrition and Cancer Prevention from the American Cancer Society suggest that most adults can drink, but they should limit their intake.

As much as 30% of breast cancer risk has been linked to the way we eat. Dietary changes to eat more fruits and vegetables may provide women with an easy way to reduce their risk of developing breast cancer. Most of the studies report that the consumption of vegetables may provide women with an easy way to reduce their risk of developing breast cancer. Most of the studies report that the consumption of vegetables is more strongly linked to breast cancer risk reduction than the consumption of fruits. Specifically, there is strong evidence for carrots and other yellow-orange vegetables such as squash and sweet potatoes, as well as dark green vegetables like broccoli and spinach. In one recent study, the consumption of more than five servings per day of vegetables versus less than three servings per day was associated with a 54% reduction in the breast cancer rate. It is not that difficult to eat five or more servings a day once you know what counts as a serving. A serving is: 1 piece of fresh fruit, ¾ cup of 100% fruit juice, ½ cup of cooked vegetables or canned fruit, 1 cup of leafy vegetables or salad, 1 handful of dried fruit, or ½ cup dried peas or beans.

The jury is still out on how meat consumption might affect breast cancer risk. Fish has no association with breast cancer risk. High protein diets are currently very popular to lose weight. Many experts are concerned with this dietary trend as high protein, low carbohydrate diets are low in fruits, vegetables, and whole grains. All are foods that have been shown repeatedly to reduce cancer risk.

Many women believe that soy consumption reduces breast cancer risk. A concern with soy is that studies of women eating soy products daily have shown that soy foods can act like estrogen and cause cell proliferation in the breast. This could have a negative effect on breast cancer survival. Phytoestrogens in soy have also been reported to both oppose and complement the effects of tamoxifen in breast cancer cells. More study is needed in this area. For now it is advised to avoid soy supplements and use soy foods in moderation. While there is a wealth of evidence that consuming more fruits, vegetables, whole grains, and even soy decreased the risk of developing cancer, there is not enough evidence to support taking any type of supplement. Some may even be harmful.

Don’t forget physical activity! New research is emerging showing that exercising can reduce the risk of cancer development. The best information at this time to reduce your risk of developing breast cancer is to increase your fruit and vegetable consumption, decrease or avoid alcohol intake, and try to exercise most days of the week. 


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