Nutrition and Physical Activity During and After Cancer Treatment: Answers to Common Questions
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, Nutrition and Physical Activity During and After Cancer Treatment: An American Cancer Society Guide for Informed Choices, 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. But many people also look to news reports and studies. 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.
No single study provides the last word on any subject. News reports may focus on what seem to be conflicting results because they are new or different, or they challenge conventional wisdom. And in brief news stories, reporters can’t always put new research findings in their proper context.
In the questions and answers listed here, we have tried to address common concerns that cancer survivors have about diet and physical activity. As you read this, keep in mind that a cancer survivor is defined as anyone who has been diagnosed with cancer at any time, whether or not the person is in treatment.
Alcohol
Does alcohol increase the risk of cancer coming back?
Studies have found a link between alcohol intake and the risk of getting a number of cancers:
- Mouth
- Throat
- Larynx (voice box)
- Esophagus (swallowing tube from mouth to stomach)
- Liver
- Breast
Alcohol use may be linked to colon cancer, too. In people who have already been diagnosed with cancer, alcohol intake could affect the risk for new cancers in these sites. Alcohol intake can also increase levels of estrogens in the blood. In theory this could increase the risk of estrogen receptor-positive breast cancer coming back after treatment, but studies so far have not addressed questions like this.
Should I avoid alcohol during cancer treatment?
The cancer type and stage (extent), as well as the type of treatment should be taken into account when deciding whether to drink alcohol during treatment. Alcohol, even in the small amounts used in mouthwashes, can irritate mouth sores and can even make them worse. It’s reasonable to avoid or limit alcohol for people with mouth sores. It may also be best to avoid or limit alcohol if you are starting treatment that will put you at risk for mouth sores, such as head and neck radiation or many types of chemotherapy.
Antioxidants
What do antioxidants have to do with cancer?
Antioxidants include vitamin C, vitamin E, carotenoids (compounds that give vegetables and fruits their colors), and many phytochemicals (plant-based chemicals). They help prevent damage to cells in the body from chemical reactions with oxygen. Because this damage may play a role in cancer development, 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 foods 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 those 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 radiation. There is a concern that the antioxidants might repair the damage to cancer cells that helps these cancer treatments work. But others have noted that the possible harm from antioxidants is only in theory. They believe that there may be a net benefit in helping to protect normal cells from damage caused by these cancer treatments.
Whether antioxidants or other supplements are helpful or harmful during chemotherapy or radiation treatment is a major question without a clear science-based answer right now. Until more evidence is available, it is best for cancer survivors getting these treatments to avoid dietary supplements that give more than 100% of the Daily Value for antioxidants.
Fat
Will eating less total fat lower the risk of cancer coming back or improve survival?
Several studies have looked at the link between fat intake and survival after the diagnosis of breast cancer, with mixed results. There is little evidence that total fat intake affects cancer outcomes, but diets high in fat tend to be high in calories, too. This may add to obesity (being seriously over weight). Obesity is tied to:
- Higher risk of several types of cancer
- Higher risk of cancer coming back after treatment
- Shorter survival for many types of cancer
Do different types of fat affect cancer risk and survival?
There is evidence that certain types of fat, such as saturated fats, may increase cancer risk. There is little evidence that other types of fat, such as mono-unsaturated fats (in canola and olive oil, olives, avocados, peanuts, and many other nuts and seeds) or polyunsaturated fats (including omega-3 fatty acids in fish and walnuts) 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 many different 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. Still, eating fiber-rich foods is recommended because they contain other nutrients that may help reduce cancer risk. They also have 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 during times when the immune system is weak. 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. Food should be handled safely; for example:
- Wash hands before eating or preparing foods.
- Wash vegetables and fruits well.
- Keep foods at the right temperatures.
- Keep raw meats and meat juices away from other foods.
For more on food safety and precautions, see our documents Infections in People With Cancer and Nutrition for the Person With Cancer During Treatment.
Meats
Should I avoid meats?
Studies have linked eating large amounts of red meat and processed meats (like bacon, hot dogs, and deli 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 coming back or getting worse (progressing or growing).
Obesity
Does being overweight increase risk of cancer coming back 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 in certain sites:
- Esophagus (swallowing tube from mouth to stomach)
- Colon and rectum
- Liver
- Gallbladder
- Pancreas
- Kidney
- Non-Hodgkin lymphoma
- Multiple myeloma
- Cancers of the stomach and prostate in men
- 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 get to and stay at a healthy weight. Avoiding weight gain is important, not only to reduce cancer risk and risk of cancer coming back, 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 certain chemicals. It has also been suggested that their nutrient makeup may be better than non-organic foods. Whether this means health benefits to those who eat organic foods is unknown.
At this time, no studies in humans exist to show whether organic foods are better than foods made or grown using the usual methods for any of these purposes:
- Reducing cancer risk
- Reducing the risk of cancer coming back
- Reducing the risk that cancer will progress (grow, spread, or get worse)
Physical activity
Should I exercise during cancer treatment and recovery?
Research strongly suggests that exercise is not only safe during cancer treatment, but it can also improve physical functioning and many aspects of quality of life. Moderate exercise has been shown to improve fatigue (extreme tiredness), anxiety, and self-esteem. It also helps heart and blood vessel fitness, muscle strength, and body composition. People getting chemotherapy and radiation may need to exercise at a lower intensity for a time, and build up more slowly than people who are not getting cancer treatment. The main goal should be to stay as active as possible.
Are there special precautions survivors should consider?
Certain issues for cancer survivors may prevent or affect their ability to exercise. Some effects of treatment may increase the risk for exercise-related problems. For example:
- People with severe anemia (low red blood cell counts) should delay activity until the anemia is better.
- Those with weak immune function should avoid public gyms and other public places until their white blood cell counts return to safe levels.
- People getting radiation should avoid swimming pools because chlorine may irritate the skin over the treatment area.
For those who were inactive before diagnosis, low-intensity activities should be started and slowly advanced. Certain people should use caution to reduce the risk of falls and injuries:
- Older people
- Those with bone disease (cancer in the bones or thinning bones, such as osteoporosis)
- People with arthritis
- Anyone with nerve damage
Can regular exercise reduce the risk of cancer coming back?
It is not known whether exercise will reduce the chances that cancer will come back or slow cancer growth. But being overweight or obese has been linked with increased risk of many types of cancer and with the risk of some cancers coming back after treatment. It is known that physical activity can help prevent and reverse weight gain. Physical activity also helps to prevent heart and blood vessel disease, diabetes, and osteoporosis. For these reasons, cancer survivors should be encouraged to have 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 coming back or getting worse (progressing) 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 plant compounds 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 foods are an excellent source of protein and can be a good option for meals without meat. Soy contains many 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 finds no special benefits or harmful effects when no more than 3 servings of soy are eaten per day as part of a healthy diet. This compares to the amounts eaten in most Asian diets. But higher doses of soy may have estrogen-like effects, and higher levels of estrogens can cause certain breast cancers to grow and spread. 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 and sugar-sweetened drinks add large amounts of calories to the diet and can cause weight gain, which can affect cancer outcomes. There are many kinds of sugars, including honey, raw sugar, brown sugar, corn syrup, and molasses. Many drinks contain sugar, such as soft drinks and fruit-flavored beverages. Most foods and drinks that are high in sugar do not offer many nutrients and may 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 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 cancer coming back?
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 create these 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 coming back?
In most studies, eating more vegetables and fruits has been linked with a lower risk of lung, oral (mouth), esophagus (swallowing tube from mouth to stomach), stomach, and colon cancer. But few studies have been done on whether a diet that includes many vegetables and fruits can reduce the risk of cancer coming back (recurrence) or improve survival. Some recent studies suggest that a higher 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 get at least 5 servings of a variety of vegetables and fruits each day because of their other health benefits. It is not known which of the compounds in vegetables and fruits are most protective. Because of this, 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. But some frozen foods can have more nutrients than fresh foods. This is 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 different forms of vegetables and fruits.
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 nutrients 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. And drinking a lot of fruit juice can add extra calories to a person’s diet. Buy juice products that are 100% vegetable or fruit juices and pasteurized to remove harmful germs. These are better for everyone, but are of special concern for people who may have weak immune systems, such as people getting chemotherapy.
Vegetarian diets
Do vegetarian diets reduce risk of cancer coming back?
No direct evidence has shown that vegetarian diets help reduce the risk of cancer coming back when compared to diets high in vegetables, fruits, and whole grains and low in red meats. But vegetarian diets can be good for you because they tend to be low in saturated fat and high in fiber, vitamins, and phytochemicals. These diets are in line with the American Cancer Society Nutrition Guidelines for the Prevention of Cancer. See our document Vegetarianism for more information.
Water and other fluids
How much water and other fluids should I drink?
Symptoms like fatigue (extreme tiredness), light-headedness, and nausea can be caused by dehydration (loss of fluid from the body). 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.
Additional resources
More information from your American Cancer Society
The following information may also be helpful to you. These materials may be ordered from our toll-free number, 1-800-227-2345, or read on our Web site, www.cancer.org.
Nutrition for the Person With Cancer During Treatment
American Cancer Society Guidelines on Nutrition and Physical Activity for Cancer Prevention
Nutrition for Children With Cancer
Infections in People With Cancer
The following books are also available from the American Cancer Society. Call us to ask about prices or to place an order:
What to Eat During Cancer Treatment
The Great American Eat-Right Cookbook
The American Cancer Society’s Healthy Eating Cookbook
National organizations and Web sites*
Along with the American Cancer Society, other sources of information include:
Food and Nutrition Information Center, U.S. Department of Agriculture (USDA)
Telephone: 301-504-5414
TTY: 301-504-6856
Web site: http://fnic.nal.usda.gov
Offers current information on dietary guidelines, food facts, and the Food Guide Pyramid, as well as information on food safety
National Cancer Institute
Toll-free number: 1-800-4-CANCER (1-800-422-6237)
TTY: 1-800-332-8615
Web site: www.cancer.gov
Has up-to-date information about cancer and cancer-related topics for patients, their families, and the general public
*Inclusion on this list does not imply endorsement by the American Cancer Society.
No matter who you are, we can help. Contact us anytime, day or night, for information and support. Call us at 1-800-227-2345 or visit www.cancer.org.
References
Doyle C, Kushi LH, Byers T, et al. Nutrition and Physical Activity During and After Cancer Treatment: An American Cancer Society Guide for Informed Choices. CA Cancer J Clin. 2006;56:323-353.
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