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