Anybody who follows the media coverage of diet-related issues has
probably experienced a great deal of frustration: one day, a particular
food is reported to have all sorts of beneficial effects, the next day
it causes some kind of disease. Indeed, all these apparent contradictions
really indicate is that we’re only just beginning to understand
the connection between diet and health -- that huge numbers of questions
remain unanswered.
The connection between diet and breast cancer risk is a perfect example
of this situation. This article gives you an overview of the current dietary
recommendations for reducing the risk of breast cancer, and provides insights
into areas of future research.
Fat and Excess Calories
Both diet and a lifestyle that contributes to an increased amount of
body fat have been linked to cancer of the breast. The average American
woman’s diet is not only high in calories but also in fat, with approximately
37 percent of her total calories being fat calories. In contrast,
the diets of women in Japan and China have, on average, fewer total calories,
with only 10 to 20 percent of calories coming from fat.
Countries with high-fat diets, such as the United States, have much
higher levels of breast cancer. American women are four to seven times
more likely to die of breast cancer as Asian women. A diet high that is
high in fat or calories resulting in an increase in body fat may promote
breast cancer by increasing levels of certain hormones, which in turn raises
circulating estrogen levels. High estrogen levels promote breast cancer
since it is an "estrogen-dependent" cancer.
However, increased breast cancer risk may actually be more a
result of excessive calorie intake, which is generally associated
with a higher fat intake, rather than the independent result of dietary
fat. Research has found that heavier women have higher estrogen levels.
This estrogen is produced by their fat cells, and therefore women who are
classified as overweight have an increased risk of breast cancer.
Some studies have found that the timing of weight gain and body
fat distribution may be more significant factors in increasing the
risk of breast cancer in such women. Specifically, weight gain starting
around the time of menopause and continuing into the postmenopausal period
-- and weight gain in the abdominal region -- have both been associated
with increased risk for breast cancer in postmenopausal women.
Types of Fat
There is an ongoing controversy regarding various types of fat. Research
has shown that polyunsaturated fats (corn and safflower oils are
two examples) and trans-fatty acids (found in margarines and partially
hydrogenated foods) have a positive association with increased breast cancer
risk.
Studies have also shown that monounsaturated fatty acids (examples
are olive oil and canola oil) do not increase -- and may even
reduce -- breast cancer risk. Finally, consuming omega-3-fatty acids
(found in fish oils, fish, and flaxseed) may possibly have a protective
effect.
Diets that are higher in plant products are usually lower in fat and
result in leaner women who have less potential for the synthesizing of
estrogen in fat tissue, and therefore a lower risk of breast cancer. Emphasizing
a vegetarian-type diet may play a key role in reducing the risk of breast
cancer. Additionally, vegetarian-style meals help increase several dietary
constituents and micronutrients (vitamins and nutrients) that may possibly
play a protective role in the incidence of breast cancer, as discussed
below.
Fiber and Antioxidants
By increasing the amount of complex carbohydrates (whole grains, fruits,
and vegetables) in your diet, you will increase your intake of fiber, vitamins,
minerals, and nutrients known as antioxidants. Antioxidants are believed
to help in the prevention of cancer. Any preventative effect antioxidants
have arises from their ability to minimize cell damage from cancer-causing
agents known as "free radicals." Antioxidants trap these "free radicals"
and prevent them from causing the type of cell damage that makes people
more susceptible to cancer.
Examples of antioxidant vitamins that may play a protective role in
preventing breast cancer include: Vitamin E, found in all oils, eggs, and
nuts; Vitamin A and Beta Carotene, found in green, orange, and yellow vegetables,
particularly carrots; Lycopene, found in tomatoes, pink grapefruit, and
watermelon; Lutein and Zeaxanthin, found in kale, collard greens, spinach,
red peppers, and romaine lettuce; and Calcium, found in milk products,
tofu, and leafy green vegetables.
Rosemary, a spice familiar to most of us, has been found to interfere
with the conversion of normal cells into cancer cells. The active compound
in this spice exhibits antioxidant properties.
Fiber may also be protective. A recent study reported that a half-cup
serving of wheat-bran cereal each morning lowered levels of estrogen in
the blood.
Phytoestrogens
There is a great deal of conflicting information concerning the association
between phytoestrogens and breast cancer. Phytoestrogen is a plant-derived
estrogen and can be found in food products like soy (tofu, tempeh, soybeans,
soy milk, and miso). It is believed that the phytoestrogens in soy act
as "anti-estrogens" -- that is, they compete with and counteract the body’s
natural estrogen, thereby helping to reduce the risk of breast cancer.
It is the particular type of phytoestrogen contained in soy, known as
isoflavones, that makes it potentially helpful in reducing a woman’s risk
of breast cancer. Isoflavones are weak estrogen-like substances; the best-known
one is Genistein. Isoflavones look like estrogen to the body and can attach
to the same sites on breast tissue as estrogen. By occupying these sites,
they may block the body's own estrogen and interfere with its cancer-causing
effect. Soy isoflavones appear to act in a way similar to the drug Tamoxifen,
which is widely used to treat breast cancer.
While some researchers believe that the phytoestrogens in soy are beneficial
for women, others are afraid that they can be dangerous for women with
breast cancer. At this time, studies are inconclusive as to the long-term
physiologic effects of the phytoestrogens contained in soy. Until more
information is available, it is a good idea not to overdo your consumption
of soy foods if you are at risk for, or have been diagnosed as having,
breast cancer.
Many other phytochemicals are under investigation as well -- "allicin"
in garlic; "ellagic acid" in grapes; "sulforaphane" in broccoli; and "indoles"
and "dithiothides" in cruciferous vegetables (broccoli, cauliflower, brussel
sprouts, cabbage, kale, mustard, and collard greens).
Alcohol
Alcohol raises the risk of breast cancer because it raises estrogen
levels. The link between alcohol and breast cancer may even be stronger
than other dietary links. Among women who consume alcohol regularly, a
clear way to reduce the risk of breast cancer is to reduce alcohol consumption.
Anything Else?
While there are many other issues to address regarding breast cancer
and nutrition, two deserve special mention. The first is "green tea," whose
consumption has been correlated with a decreased recurrence of Stages I
and II of breast cancer. Also, Vitamin D from sunlight, rather than dietary
Vitamin D, has been shown to decrease risk.
What to Do?
Dietary guidelines should be a part of a sensible lifestyle approach,
as breast cancer research continues to investigate the role of diet. At
this time, based on the data available, the following diet and lifestyle
modifications are generally recommended and should be incorporated into
your daily activity:
- Remain physically active and lean throughout life
- Consume a high intake of fruits and vegetables
- Consume less fatty foods
- Limit alcohol intake
- Increase consumption of whole grains and legumes
- Eat a variety of foods
- Limit or control obesity through a decreased caloric intake
Nutritional counseling can help incorporate these guidelines into an individual
meal plan. It can provide specific guidelines as to calories, grams of
fat, and grams of fiber, as well as vitamin/mineral regimens that can be
designed to fit into any lifestyle.
Overweight women -- especially those with coexisting risk factors for
breast cancer -- should try to lose weight, or at least avoid gaining weight.
Even with all the questions that have yet to be fully answered, it’s
clear that following the above guidelines can play an important role in
reducing your risk for breast cancer.
