Dietary changes that may be helpful
The following dietary changes have been studied in connection with cancer.
Alcohol and Cancer
Alcohol consumption significantly increases the risk of cancers of the mouth
(oral/oropharyngeal cancer), throat (esophageal cancer), and voice box (laryngeal cancer),
particularly in conjunction with cigarette smoking.1 2 3 Most
studies documenting these associations also report that former drinkers have significantly
lower risks for these cancers compared with current drinkers. Strong correlations between
alcohol consumption and the risk of having liver cancer have also been reported.4
5
Little is known about the effect of alcohol intake on the risk of female cancers other than
breast cancer. Of the few published studies, findings have been inconsistent.6
7 8 9
Fiber
Whole grains (such as
rye, brown rice, and whole wheat) contain high amounts of insoluble fiber—the type of
fiber some scientists believe may help protect against a variety of cancers. In an analysis of
the data from many studies, people who eat relatively high amounts of whole grains were
reported to have low risks of lymphomas and cancers of the pancreas, stomach, colon, rectum,
breast, uterus, mouth, throat, liver, and thyroid.10 Most research focusing on the
relationship between cancer and fiber has focused on breast and colon cancers.
Consuming a diet high in insoluble fiber is best
achieved by switching from white rice to brown rice
and from bakery goods made with white flour or mixed
flours to 100% whole wheat bread, whole rye
crackers, and whole grain pancake mixes. Refined white flour is generally listed on food
packaging labels as “flour,”“enriched flour,”“unbleached
flour,”“durum wheat,”“semolina,” or “white flour.”
Breads containing only whole wheat are often labeled “100% whole wheat.”
Vegetarianism
The following two possibilities are both strongly supported by research findings:
- Some foods consumed by vegetarians may protect against cancer.
- Eating meat may increase the risk of cancer.
Compared with meat eaters,
most,11 but not all,12 studies have found that vegetarians are less
likely to be diagnosed with cancer. Vegetarians have also been shown to have stronger immune function, possibly explaining why vegetarians may
be partially protected against cancer.13 Female vegetarians have been reported to
have lower estrogen levels compared with meat-eating women, possibly explaining a lower
incidence of uterine and breast cancers.14 A reduced risk for various cancers is
only partly,15 not totally,16 explained by differences in body weight,
smoking habits, and other lifestyle issues.
Fruits and Vegetables
Consumption of fruits and vegetables is widely accepted as lowering the risk of most common
cancers.17 Many doctors recommend that people wishing to reduce their risk of
cancer eat several pieces of fruit and several portions of vegetables every day. Optimal
intakes remain unknown.
Most doctors also recommend that people should not consider supplements as substitutes for
the real thing. Some of the anticancer substances found in produce have probably not yet been
discovered, while others are not yet available in supplement form. More important, some
research, particularly regarding synthetic
beta-carotene, does not support the idea that taking supplements has the same protective
value against cancer as does consumption of fruits and vegetables.
Flavonoids
Flavonoids are found in virtually all herbs and plant foods. Consumption of flavonoid-rich onions and apples
contain large amounts of one flavonoid called quercetin.
Consumption of flavonoids in general, or quercetin-containing foods in
particular,18 has been associated with protection against cancer in
some,19 but not all,20 preliminary studies.
Tomatoes
Tomatoes contain lycopene—an antioxidant similar in structure to beta-carotene. Most lycopene in our diet comes from tomatoes,
though traces of lycopene exist in other foods. Lycopene inhibits the proliferation of cancer
cells in test tube research.21
A review of published research found that higher intake of tomatoes or higher blood levels
of lycopene correlated with protection from cancer in 57 of 72 studies. Findings in 35 of
these studies were statistically significant.22 Evidence of a protective effect for
tomato consumption was strongest for cancers of the prostate, lung, and stomach, but some
evidence of a protective effect also appeared for cancers of the pancreas, colon, rectum,
esophagus (throat), mouth, breast, and cervix.
Cruciferous vegetables
Cabbage,
Brussels sprouts, broccoli, and cauliflower belong to the Brassica family of vegetables,
also known as “cruciferous” vegetables. In test tube and animal studies, these
foods have been associated with anticancer activity,23 possibly due to several
substances found in these foods, such as
indole-3-carbinol,24 glucaric acid (calcium D-glucarate),25 and sulforaphane.26 In a preliminary human study, people
who ate cruciferous vegetables were reported to have a lower-than-average risk for bladder
cancer.27
Meat (how it is
cooked) and childhood cancers
In one report, high consumption of hot dogs was associated with an almost tenfold increase in
the risk of childhood leukemia when compared with low consumption.28 In another
report, maternal consumption of hot dogs and childhood consumption of hamburgers or hot dogs
at least once per week were associated with a doubling of the risk of cancers in
children.29 A review of nine studies found an association between consumption by
pregnant women of cured meat and the risk of brain cancer in their offspring.30
These associations do not yet constitute proof that eating hot dogs or hamburgers causes
cancer in children, and evidence linking cured meat consumption to childhood cancers remains
somewhat inconsistent.31
In the report studying the effects of eating hot dogs and hamburgers, the association
between meat eating and leukemia was weakest among children who took vitamin supplements. Processed meats, such as hot dogs,
contain nitrates and nitrites—precursors to carcinogens. Antioxidants found in multivitamins keep nitrates and nitrites
from converting into those carcinogens. Therefore, the association between vitamin consumption
in children and protection against childhood cancers remains plausible, though unproven.
Fish
Fish eaters have been reported to have low risks of cancers of the mouth, throat, stomach,
colon, rectum, pancreas,32 lung,33 breast,34 and
prostate.35 The omega-3 fatty acids found in
fish are thought by some researchers to be the components of fish responsible for protection
against cancer.36
Coffee
Years ago, researchers reported the greater the consumption of coffee in a country, the higher
the risk of pancreatic cancer in that country.37 An analysis of data from studies
published between 1981 and 1993 did find some association between high consumption of coffee
and an increased risk of pancreatic cancer.38 Surprisingly, however, the same
report found that people drinking only one or two cups of coffee per day had, on average, a
lower risk of pancreatic cancer compared with people who never drink coffee.
Most,39 40 41 but not all,42 published reports
have shown coffee drinkers are at increased risk of bladder cancer, though in one case the
relationship was found only in men.43 In another study, the association was found
only with caffeinated coffee.44 A review of 35 trials found a small (7%) increased
risk of bladder cancer in coffee drinkers compared with people not drinking coffee—a
difference not statistically significant.45
Calories
Scientists have known for many years that severe restriction of calories dramatically reduces
the risk of cancer in laboratory animals.46 Scientists speculate that caloric
content of the human diet may also affect cancer rates,47 though much less is known
about the effect, if any, of moderate caloric restrictions in humans. In one report, adults
with cancer were more likely to have consumed more calories during childhood compared with
healthy adults.48 In other reports, attempts to find associations between reduced
intake of calories and cancer have produced mixed results.49 50
51
Only severe restriction in caloric intake provides significant protection in
animal studies. As most people are unlikely to severely restrict calories, the association
between caloric restriction and protection from cancer may ultimately prove to only be of
academic interest.
Dietary Fat
In studying data from country to country, incidence of ovarian cancer correlates with dietary
fat intake.52 According to preliminary research, consumption of saturated fat, dietary cholesterol (as found in eggs),53 and animal fat in general54
correlates with the risk of ovarian cancer.
Preliminary studies suggest dietary fat may correlate with the risk of uterine
cancer.55 Some of the excess risk appears to result from increased body weight that
results from a high-fat diet.56
Many years ago, researchers reported that animals on a high-fat diet formed skin cancers
more rapidly than did other animals.57 Although some preliminary human research has
found no relationship between dietary fat intake and the risk of skin cancer,58
patients with basal cell and squamous cell skin cancers who were put on a low-fat diet for two years were reported to show a significant
decrease in the number of new skin cancers compared with patients who maintained a high-fat
diet.59 Similarly, precancerous lesions of the skin have been prevented in people
put on a low-fat diet.60
Polyunsaturated
Fats
A chain of carbon atoms in which several are not attached to the maximum possible amount of
hydrogen is called “polyunsaturated”––in other words, unsaturated with
hydrogen in several places. When nutrition researchers talk about polyunsaturated fatty acids,
they are often referring primarily to linoleic acid—a fatty acid found in nuts and seeds and most vegetable oils.
In animal research, the consumption of polyunsaturated fatty acids increases the risk of
some cancers.61 However, in humans, most,62 63 64
though not all,65 reports do not find an association between polyunsaturates and
cancer risks.
Sugar
A preliminary study has reported an association between an increasing intake of sugar or
sugar-containing foods and an increased risk of gallbladder cancer.66 Whether this
association exists because sugar directly promotes cancer or because sugar consumption is only
a marker for some other dietary or lifestyle factor remains unknown.
Salt
In preliminary research, increasing intake of salt correlates with increased risk of stomach
cancer.67 68 Associations between foods preserved with salt and the risk
of cancers of the head and neck have also been reported.69
Animal studies suggest that the antioxidant or immune-enhancing effect of whey protein may produce anti-cancer effects.70
71 72 Preliminary human case reports suggest that 30 grams per day of
whey protein may improve responses to anti-cancer medications, but more research is
needed.73
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