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Information for Nurses and Physicians
Diet and Cancer Prevention
Recently, noted English epidemiologists Sir
Richard Doll, MD, DSc, and Richard Peto, MD,
estimated that between 20 and 60% of cancer
deaths were related to dietary factors. Much
of cancer may be preventable. However, the
exact relationship between dietary ingredients
and cancer is elusive, and many major questions
remain. Among the complicating factors:
- The complexity of the diet in terms of
biochemical components
- There are more than 100 types of cancers
with different causes
- It is difficult to do controlled studies
on human populations
- Cancer takes many years to develop; therefore,
it is hard to prove a cause and effect relationship
- Dietary ingredients may increase as well
as decrease the risk of cancer
In response to the urgent need for more research,
the American Cancer society (ACS) has supported
many grants that have collected dietary information
from the population, studied nutritional prevention,
and encouraged the development of centers
of excellence in cancer research and nutrition.
The outcome of some of this research has lead
to the Society's following guidelines on diet
and nutrition.
Fruits and Vegetables Reduce Cancer
Risk
There is strong support for a diet rich in a
variety of fruits and vegetables. These foods
contain an abundance of minerals, vitamins,
biochemical compounds, and fiber which may decrease
the risk of cancer. Further, an individual who
eats an adequate amount of fruits and vegetables
is likely to eat proportionately less fatty
and high-calorie foods. Research has revealed
that a diet rich in vegetables is linked to
a significant decrease in risk of colon cancer
in both men and women (Journal of the National
Cancer Institute, October, 1992). In addition,
cruciferous vegetables such as broccoli, cabbage,
and cauliflower may help prevent certain cancers
(e.g., breast cancer).
Vitamins and Nutrients May Help Prevent
Cancer
Currently, researchers are examining the value
of antioxidant vitamins and nutrients in the
diet. These chemicals interfere with oxidation,
a process that can result in formation of carcinogens.
For example, the carotenoids (derivatives of
Vitamin A), Vitamin E, and Vitamin C are considered
antioxidants.
Research on the role of antioxidants in reducing
the risks of cancer and heart disease has
recently been examined by the Food and Drug
Administration (FDA). There is still no significant
evidence supporting specific recommendations.
However, experts agree that people should
eat at least five servings of fruits and vegetables
daily, which would provide an adequate amount
of antioxidants.
The Importance of Fiber
Fiber can be found in fruits, vegetables, and
whole grain cereals that are not readily digested.
Research is currently in progress to investigate
the role of different kinds of fiber in the
prevention of cancer. So far, some of these
studies have shown that a high-fiber diet may
help to prevent colon cancer. These results
have lead the American Cancer Society, National
Cancer Institute (NCI), U.S. Department of Agriculture,
and the American Heart Association (AHA) to
recommend a high-fiber diet.
Fat and Cancer
Most animal studies have shown that a low-fat
diet decreases overall cancer risk. However,
some epidemiological studies suggest that a
low-fat diet may have a greater influence on
reducing the risk of only certain kinds of cancers.
In addition, different types of fat may affect
cancer risks differently. Further, the elevated
calories in a high-fat diet may confound the
effect of fat alone on the risk of cancer.
As a result of these uncertainties, research
studies are attempting to isolate the specific
relationship between fat and cancer. For example,
the NCI is funding a Women's Health Initiative
study to determine if a low-fat diet can reduce
the risk of breast cancer. A study by Dr.
Rose, chief of the nutrition and endocrinology
division at the American Health Foundation
in New York, has shown that omega-6 unsaturated
fatty acids increase metastasis of human breast
cancer cells in mouse mammary tissue. Dr.
Pour, professor of pathology at the Eppley
Institute, is trying to determine whether
the excess calories or the fat in a high-fat
diet increases the risk of pancreatic cancer
in rodents.
Despite the need for the further research
on fat and cancer, the ACS, NCI, and AHA continue
to advocate a low-fat diet.
Chemoprevention
In cancer chemoprevention, synthetic or natural
substances are used to deter the carcinogenic
process. As discussed previously, diet is an
important source for chemoprevention because
a small daily dose of harmless or relatively
harmless substances can aid in diminishing disease.
Dr. Hong, a professor at the M.D. Anderson Cancer
Center in Houston, has used chemopreventive
agents related to Vitamin A to combat epithelial
cancers of the aerodigestive tract.
Aspirin has also been used in the intervention
of cancer. For example, in a CPS-II population
study supported by the ACS, Dr. Thun has found
that aspirin may have a protective effect
against certain types of cancer (e.g., colon
cancer). Participants who also had diets rich
I fruits and vegetables had a further reduction
in cancer risk. Patients need to see their
physicians before starting aspirin therapy.
Other dietary substances such as garlic oil,
retinoids, and glutathione are also being
studied for relationship to cancer. Dr. Kinkade,
biochemistry professor at Emory University,
has found that glutathione has a protective
effect against certain chemical carcinogens,
and may decrease the risk of colon cancer.
In another study by Dr. Walaszek, at the M.D.
Anderson Cancer Center in Texas, D-glucaric
acid (plant product) has inhibited the initiation
and progress of breast cancer in rats.
Researchers are also investigating the negative
effect of diet on cancer risks. There are
natural ingredients and contaminants in food
that can be carcinogenic. Carcinogens may
also develop from the way food is prepared,
such as via charcoal-broiled or smoked methods.
Since proper nutrition can reduce the risk
for cancer, it is important that people maintain
healthy diets and follow the American Cancer
Society Guidelines on Diet and Nutrition.
In particular, cancer patients may sometimes
be challenged to modify their diets. Those
patients undergoing chemotherapy often develop
an aversion to their usual nutritious diets
because of the nausea that is induced by certain
chemicals. To maintain proper nutrition, Dr.
Andresen, at the Carle Foundation in Illinois,
has studied the use of "scapegoat" foods.
These are foods that are foreign to a patient's
normal diet and that may serve as a substitute
for the aversive foods. Dr. Andresen is currently
analyzing different methods of incorporating
scapegoat foods into a patient's normal diet.
ACS Guidelines on Diet and Nutrition
To help people make educated choices, the Society
publishes guidelines to advise on dietary practices
that may reduce the risk of cancer. The guidelines
are meant to be practiced as a whole, creating
a total dietary pattern to follow for lowered
cancer risk.
- Maintain a desirable body weight
- Eat a varied diet
- Include a variety of vegetables and fruits
in the daily diet
- Eat more high-fiber foods such as whole
grain cereals, legumes, vegetables, and
fruits
- Cut down total fat intake
- Limit consumption of alcoholic beverages
- Limit consumption of salt-cured, smoked,
and nitrite-preserved foods
Source: American
Cancer Society (1994). Research News,
3(1).
(Submitted by Neeru Khanuja,
Research Assistant) |
