Fruits and Vegetables
Does eating vegetables reduce the risk of breast cancer?
Yes. The number of servings of vegetables in a woman's daily diet makes a large difference in her risk of breast cancer. Women who eat a diet rich in vegetables have a lower incidence of breast cancer. Each daily serving of a colorful, or non-starchy, vegetable is associated with a 10% reduction in the risk of breast cancer -- even after accounting for weight and other known risk factors for breast cancer.
In studies on both premenopausal women in New York and postmenopausal women in Athens, Greece, those who ate more than five servings of colorful vegetables a day had breast cancer only half as often as women who ate less than three servings a day. The possibility of cutting one's breast cancer risk by 50% or more is an extremely important finding.
What is a colorful vegetable?
The vegetables that appear to affect breast cancer risk are the so-called colorful vegetables -- that is, non-starchy vegetables. Broccoli, cabbage, carrots, tomatoes, peppers, and dark leafy green vegetables all qualify. Potatoes and other starchy vegetables do not. As a rule, any vegetable that has a deep green, red, yellow, or orange color is rich in antioxidants and nutrients as well as fiber. Although researchers do not understand all the reasons why a diet rich in these vegetables decreases a woman's risk of breast cancer, the findings consistently show that they do.
Why do colorful vegetables make a difference?
The first research studies conducted on vegetable consumption and breast cancer showed that women who ate the lowest number of vegetable servings had, on average, a 25–30% higher risk of breast cancer than women who ate the highest number of vegetable servings. A difference of 30% in risk is quite important, but it isn't huge. As researchers realized vegetable consumption might affect the risk of breast cancer, the questions about the types of vegetables women were eating became more precise. The result of this more stringent line of questioning was the discovery of the benefits of colorful vegetables.
White potatoes account for 40% of the servings of vegetables eaten in the United States every day. White potatoes are perfectly good vegetables and are an important source of energy and several vitamins and minerals. However, they do not appear to affect the risk of breast cancer.
How many servings of vegetables should be eaten each day?
Each daily serving of a colorful, or non-starchy, vegetable is associated with a 10% reduction in the risk of breast cancer. The U.S. Department of Agriculture dietary guidelines recommend eating at least 3–5 servings of vegetables and 2–4 servings of fruit a day. The average American woman eats 1.8 servings of colorful vegetables a day. The average woman under 40 eats only 1.5 servings.
Does eating fruit decrease the risk of breast cancer?
Although fruits are also associated with a lower risk of breast cancer, the evidence is not as consistent and the effect is not quite as large as they are for vegetables. Each additional serving of fruit or fruit juice beyond the average 1.2 servings of fruit a day is associated with a drop of around 8% in the risk of breast cancer.
It is difficult to compare the risk figures for fruits and vegetables from the different studies, because half of the studies consider tomatoes a fruit (which they are, technically) and the other half consider them vegetables (since that is the opinion of most people). No matter what the category, consumption of one additional medium-size tomato a day decreases the risk of breast cancer by about 10%.
Are specific nutrients in fruits and vegetables responsible for the decrease in risk?
Research indicates that it is the fruits and vegetables themselves, with their natural package of nutrients, that lower the risk of breast cancer. No individual nutrient has been identified as being responsible for the reduction in risk.
Most of the older research on vegetable consumption and the risk of breast cancer evaluated the nutritional value of fruits and vegetables by measuring the micronutrients, antioxidant vitamins, carotenoids, or other phytochemicals believed to be the active anticancer components. There were no consistent differences in the risk of breast cancer for high levels versus low levels of any nutrient, whether these levels were measured by diet questionnaires or by blood samples. Newer studies show that eating colorful fruits and vegetables makes a difference in the risk of breast cancer, even though no particular responsible component in any fruit or vegetable could be identified.
Will new research show a benefit of particular nutrients?
Several of the recently identified constituents of various plant foods are being investigated for anticancer activity in laboratory studies. Cruciferous vegetables contain indole-3-carbinol, which affects the metabolism of estrogen. Soy contains the isoflavones genistein, daidzein, and others, which have specific effects on tumor cells in test tubes. Olive oil and flaxseed contain long-chain fatty acids that might modify the risk of breast cancer. Any of these chemical constituents of plant foods could turn out to be useful in preventing breast cancer in human populations, but at present, it is not known.
Current research has shown that antioxidant vitamins, carotenoids, and other micronutrients affect cancer cells in test tubes and rodents, but no measurable effect has been found in studies among human females. Women who eat more broccoli, cabbage, carrots, green vegetables, and soy foods are known to have lower rates of breast cancer, even though researchers do not understand the exact mechanisms of action.
