This document
is part of an article developed by the American Cancer Society 2006
Nutrition, Physical Activity and Cancer Survivorship Advisory
Committee. The full article, written for heath care professionals, is
published in the November/December 2006 issue of CA: A Cancer Journal
for Clinicians. It is available for free online at:http://caonline.amcancersoc.org/content/vol56/issue6/.
Cancer survivors often look for information and advice from
their health care providers about food choices, physical activity, and
dietary supplement use to improve their quality of life and survival.
It's important to point out that no single study provides the last word
on any subject. And news reports may focus on what seem to be
conflicting results because they are new or different, or they
challenge conventional wisdom.
In brief news stories, reporters can't always put new research
findings in their proper context. The best advice about diet and
physical activity is that it is rarely a good idea to change diet or
activity levels based on a single study or news report. The following
questions and answers address common concerns that cancer survivors
have about diet and physical activity.
Alcohol
Does alcohol
increase the risk of cancer recurrence?
Studies have found a link between alcohol intake and risk of
getting cancers of the mouth, throat, larynx (voice box), esophagus,
liver, breast, and probably colon. In people who have already been
diagnosed with cancer, alcohol intake could also affect the risk for
new cancers of these sites. Alcohol intake can increase levels of
estrogens in the blood, which in theory could increase the risk for
recurrence of estrogen receptor-positive breast cancer, but studies
done to date have not addressed questions like this.
Should alcohol
be avoided during cancer treatment?
The cancer type and stage (extent), as well as the type of
treatment should be taken into account when considering alcohol use
during treatment. Alcohol, even in the small amounts found in
mouthwashes, can be irritating to survivors with mouth sores and can
even make them worse. It's reasonable to recommend that alcohol intake
should be avoided or limited in survivors with mouth sores, as well as
in those starting head and neck radiation or a chemotherapy regimen
that puts them at risk for this problem.
Antioxidants
What do
antioxidants have to do with cancer?
Antioxidants include vitamin C, vitamin E, carotenoids, and
many phytochemicals. They help prevent damage to cells in the body from
chemical reactions with oxygen. Because this damage may be important in
the development of cancer, it has long been thought that antioxidants
may help prevent cancer. Studies suggest that people who eat more
vegetables and fruits, which are rich sources of antioxidants, may have
a lower risk for some types of cancer. Because cancer survivors may be
at increased risk for second cancers, they should eat a variety of
antioxidant-rich foods each day. So far, studies of antioxidant vitamin
or mineral supplements have not found that they reduce cancer risk. The
best advice at this time is to get antioxidants through food sources
rather than supplements.
Is it safe to
take antioxidant supplements during cancer treatment?
Many dietary supplements contain levels of antioxidants (such
as vitamins C and E) that are much greater than the amount recommended
in the Dietary Reference Intakes for optimal health. At this time, many
cancer doctors advise against taking higher doses of antioxidant
supplements during chemotherapy or radiotherapy because they could
repair the damage to cancer cells that helps these treatments work. But
others have noted that the possible harm from antioxidants is only in
theory, and that there may be a net benefit by helping to protect
normal cells from the collateral damage from these cancer treatments.
Whether antioxidants or any other dietary supplements are
helpful or harmful during chemotherapy or radiotherapy is a critical
question without a clear scientific answer at this time. Until more
evidence is available that suggests more benefit than harm, it is best
for cancer survivors getting these treatments to avoid dietary
supplements that are more than 100% of the Daily Value for
antioxidants.
Fat
Will eating less
total fat lower the risk of cancer recurrence or improve survival?
Several studies have looked at the link between fat intake and
survival after the diagnosis of breast cancer, with mixed results.
Although there is little evidence that total fat intake affects cancer
outcomes, diets high in fat tend to be high in calories. This may add
to obesity, which in turn is linked with increased cancer risk at
several sites, increased risk of recurrence, and reduced chances of
survival for many cancer sites.
Do different
types of fat affect cancer risk and survival?
There is evidence that certain types of fat, such as saturated
fats, may have an effect on increasing cancer risk. There is little
evidence that other types of fat, such as omega-3 fatty acids (found
mainly in fish), mono-unsaturated fats (found in olive and canola
oils), or other polyunsaturated fats reduce cancer risk.
In one study, high saturated fat intake reduced prostate
cancer-specific survival, and in another, mono-unsaturated fat intake
lowered the risk of death from prostate cancer. Excess saturated fat
intake is a known risk factor for heart disease, a major cause of death
in all populations, including cancer survivors.
Although trans fats have harmful effects on the heart, such as
raising blood cholesterol levels, their link to cancer risk or survival
is not clear. Still, survivors (especially those at increased risk of
heart disease) should eat as few trans fats as possible. Major sources
of trans fats are margarines and snack foods that contain partially
hydrogenated oils.
Fiber
Can dietary
fiber prevent cancer or improve cancer survival?
Dietary fiber includes a wide array of plant carbohydrates
that are not digested by humans. Fibers are either "soluble" (like oat
bran) or "insoluble" (like wheat bran and cellulose). Soluble fiber
helps lower the risk of heart disease by reducing blood cholesterol
levels. Fiber is also linked with improved bowel function. Good sources
of fiber are beans, vegetables, whole grains, and fruits.
Links between fiber and cancer risk are weak, but eating these
foods is still recommended because they contain other nutrients that
may help reduce cancer risk and provide other health benefits, such as
reduced risk of heart disease.
Food Safety
Are there
special food safety precautions for people getting cancer treatment?
Infection is of special concern for cancer survivors,
especially if the immune system is weakened. This can happen with
certain cancer treatments, such as chemotherapy. During such
treatments, survivors should be careful to avoid eating foods that may
contain unsafe levels of germs. General food safety practices, such as
washing hands before eating, washing vegetables and fruits well, and
keeping foods at proper temperatures, should be encouraged, and
survivors should be taught about food safety.
Meats
Should I avoid
meats?
Several studies have linked eating large amounts of red meat
and processed meats with increased risk of colorectal, prostate, and
stomach cancers. Some research suggests that frying, broiling, or
grilling meats at very high temperatures creates chemicals that might
increase the risk of some types of cancer. For these reasons, American
Cancer Society Guidelines for cancer prevention recommend limiting
intake of processed and red meats.
No studies have looked at the effect of processed meat, meat
cooked at high temperature, or meat in general on cancer recurrence or
progression.
Obesity
Does being
overweight increase risk of cancer recurrence or getting another cancer?
More and more evidence suggests that being overweight raises
the risk for recurrence and reduces the odds of survival for many
cancers. Increased body weight has been linked with higher death rates
for all cancers combined. It has also been linked with increased risk
for cancers of the esophagus, colon and rectum, liver, gallbladder,
pancreas, kidney, non-Hodgkin lymphoma, and multiple myeloma, as well
as to cancers of the stomach and prostate in men and cancers of the
breast, uterus, cervix, and ovary in women.
Because of other proven health benefits to losing weight,
people who are overweight are encouraged to lose weight and maintain a
healthy weight. Avoiding weight gain as an adult is important not only
to reduce cancer incidence and risk of recurrence, but the risk of
other chronic diseases as well.
Organic foods
Are foods
labeled organic
recommended for cancer survivors?
The term organic
is often used for plant foods grown without pesticides and genetic
modifications, and for meat, poultry, eggs, and dairy products that
come from animals that are given no antibiotics or growth hormones. The
use of the term organic
on food labels is regulated by the US Department of Agriculture. It is
commonly thought that organic foods may be more healthful because they
reduce exposure to some chemicals. It has also been suggested that
their nutrient composition may be better than non-organic foods.
Whether this translates into health benefits is unknown.
At this time, no studies in humans exist to show whether such
foods are better at reducing cancer risk, recurrence, or progression
than foods made by other farming and production methods.
Physical activity
Should I
exercise during cancer treatment and recovery?
Research strongly suggests that exercise is not only safe and
feasible during cancer treatment, but that it can also improve physical
functioning and many aspects of quality of life. Moderate exercise has
been shown to improve fatigue, anxiety, and self-esteem, as well as
heart and blood vessel fitness, muscle strength, and body composition.
People getting chemotherapy and radiation therapy who are already on an
exercise program may need to exercise at a lower intensity for a time
and progress at a slower pace compared to people who are not getting
cancer treatment. The main goal should be to maintain activity as much
as possible.
Are there
special precautions survivors should consider?
Issues for cancer survivors may prevent or affect their
ability to exercise. Some effects of treatment may increase the risk
for exercise-related injuries and other effects. For example, survivors
with severe anemia (low red blood cell counts) should delay activity
until the anemia is improved; people with weakened immune function
should avoid public gyms and other public places until their white
blood cell counts return to safe levels; those getting radiation should
avoid swimming pools because chlorine exposure may irritate irradiated
skin.
For those who were inactive before diagnosis, low-intensity
activities should be started and slowly advanced. For older people and
those with bone disease (due to spread of cancer to the bones or to
osteoporosis), arthritis, or nerve damage, caution should be used to
reduce the risk for falls and injuries.
Can regular
exercise reduce the risk of cancer recurrence?
It is not known whether exercise will reduce the chances of
cancer recurrence or slow cancer growth. But being overweight or obese,
which is affected by physical activity, has been linked with increased
risk of many types of cancer and with risk of recurrence of some
cancers. Physical activity also helps to prevent heart and blood vessel
disease, diabetes, and osteoporosis. For these reasons, cancer
survivors should be encouraged to adopt a physically active lifestyle.
Phytochemicals
What are
phytochemicals, and do they reduce cancer risk?
The term phytochemicals
refers to a wide range of compounds made by plants. Some have either
antioxidant or hormone-like actions. Studies looking at the effects of
phytochemicals on cancer recurrence or progression are very limited.
The little data that exists is mixed or comes from only a few studies.
Eating lots of vegetables and fruits reduces the risk of some types of
cancer, so researchers are looking for the specific components that
might account for this. At this time there is no evidence that
phytochemicals taken as supplements are as helpful as the vegetables,
fruits, beans, and grains they come from.
Soy products
Should cancer
survivors include soy-based foods in the diet?
Soy-derived foods are an excellent source of protein and can
be a good alternative to meat. Soy contains several phytochemicals,
some of which have weak estrogen activity and seem to protect against
hormone-dependent cancers in animal studies. Other compounds in soy
have antioxidant or other helpful properties. There is a great deal of
interest in the possible role of soy foods in reducing cancer risk in
general and breast cancer in particular. But the evidence for such a
role is mixed.
For the breast cancer survivor, current research suggests
neither specific benefits nor harmful effects when soy is eaten in the
moderate amounts found in most Asian diets (no more than 3 servings per
day) as part of a healthy diet. But higher doses of soy may have
estrogen-like effects, and higher levels of estrogens clearly increase
the risk for progression of some breast cancers. For this reason, it is
best for breast cancer survivors to avoid the high doses that are found
in more concentrated sources such as soy powders and isoflavone
supplements.
Sugar
Does sugar
"feed" cancer?
No. Sugar intake has not been shown to directly increase the
risk of getting cancer or having it progress. But sugars (including
honey, raw sugar, brown sugar, corn syrup, and molasses) and beverages
that contain them (such as soft drinks and fruit-flavored beverages)
add large amounts of calories to the diet and can cause weight gain,
which can affect cancer outcomes. Most foods and beverages that are
high in sugar do not add many nutrients to the diet and often replace
more nutritious food choices. For this reason, limiting sugar intake is
recommended.
Supplements
Would survivors
benefit from using vitamin and mineral supplements?
During and after cancer treatment, there is a probable benefit
of taking a standard multiple vitamin and mineral supplement that
contains about 100% of the Daily Values because during these times, it
may be hard to eat a diet with enough of these nutrients. The use of
very large doses of vitamins, minerals, and other dietary supplements
is not recommended because evidence exists that some high-dose
supplements may increase cancer risk.
Can nutritional
supplements lower cancer risk or the risk of recurrence?
There is strong evidence that a diet rich in vegetables,
fruits, and other plant-based foods may reduce the risk of some types
of cancer. And some recent studies suggest there may be a helpful
effect on recurrence or survival for breast, prostate, and ovarian
cancers. But there is no evidence at this time that supplements can
provide these benefits. Many healthful compounds are found in
vegetables and fruits, and it is likely that these compounds work
together to exert their helpful effects. There are likely to be
important, but as of yet unknown, compounds in whole foods that are not
in supplements. Food is the best source of vitamins and minerals.
Vegetables and fruits
Will eating
vegetables and fruits lower risk of cancer recurrence?
Eating more vegetables and fruits has been linked in most
studies with a lower risk of lung, oral, esophagus, stomach, and colon
cancer. But few studies have been done on whether a diet including many
vegetables and fruits can reduce the risk of cancer recurrence or
improve survival. Some recent studies suggest increasing intake of
vegetables may have a helpful effect on recurrence or survival for
breast, prostate, and ovarian cancers, but this is not definite.
Still, cancer survivors should be encouraged to get at least 5
servings of a variety of vegetables and fruits each day because of
their other health benefits. Because it is not known which of the
compounds in vegetables and fruits are most protective, the best advice
is to eat 5 or more servings of different kinds of colorful vegetables
and fruits each day.
Is there a
difference in the nutritional value of fresh, frozen, and canned
vegetables and fruits?
Yes, but they can all be good choices. Fresh foods are usually
thought to have the most nutritional value. Often, though, frozen foods
can be more nutritious than fresh foods because they are often picked
ripe and quickly frozen, whereas nutrients can be lost in the time
between harvest and eating fresh foods. Canning is more likely to
reduce the heat-sensitive and water-soluble nutrients because of the
high temperatures needed in the canning process. Be aware that some
fruits are packed in heavy syrup, and some canned vegetables are high
in sodium. Choose vegetables and fruits in a variety of forms.
Does cooking
affect the nutritional value of vegetables?
Boiling vegetables, especially for long periods, can leach out
their water-soluble vitamins. Microwaving and steaming are the best
ways to preserve the nutritional content in vegetables.
Should I be
juicing my vegetables and fruits?
Juicing can add variety to the diet and can be a good way to
get vegetables and fruits, especially for those who have trouble
chewing or swallowing. Juicing also helps the body absorb some of the
nutrients in vegetables and fruits. But juices may be less filling than
whole vegetables and fruits and contain less fiber. Fruit juice, in
particular, can add excess calories to one's diet if large amounts are
consumed. Commercial juice products should be 100% vegetable or fruit
juices and should be pasteurized to remove harmful germs. This is true
for the general population, but is of special concern for people who
may have weak immune systems, such as cancer patients getting
chemotherapy.
Vegetarian diets
Do vegetarian
diets reduce risk of cancer recurrence?
No direct evidence has shown whether eating a vegetarian diet
has any added benefit for reducing cancer recurrence when compared to a
diet high in vegetables, fruits, and whole grains and low in red meats.
But vegetarian diets can have many healthful traits because they tend
to be low in saturated fat and high in fiber, vitamins, and
phytochemicals. These diets are consistent with the American Cancer
Society Nutrition Guidelines for the Prevention of Cancer.
Water and other fluids
How much water
and other fluids should I drink?
Symptoms like fatigue, light-headedness, and nausea can be
caused by dehydration. To help prevent these problems, survivors should
be encouraged to try to take in enough fluids. Drinking water and other
liquids may also reduce the risk of bladder and colon cancer. Drinking
at least 8 eight-ounce servings of liquid a day is usually advised for
the general public. This is reasonable advice for survivors, too, with
the exception of those who have a specific medical reason for
restricting fluid intake.
Revised: 03/20/08
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