Diet and Cancer

Diet and Cancer

Reviewed By:
Mark Oren, M.D., FACP


Good nutrition is beneficial for everyone. A healthy, balanced diet may reduce the risk of numerous diseases, including some forms of cancer. For example, diets low in saturated fat have been shown to decrease the risk for colorectal cancer and prostate cancer.

Over the years, researchers have conducted extensive studies examining the association of diet, nutrition and cancer. Although the association is not completely understood, nutrition plays a significant role in the development of certain cancers. Studies have evaluated dietary factors for the risk and prevention of cancer as well as their effect on treatment. The American Cancer Society’s dietary guidelines for cancer prevention recommend that individuals:

  • Eat at least five servings of fruits and vegetables every day.

  • Choose whole grains instead of refined (processed) grains and sugars.

  • Limit consumption of red meat, especially processed meats and those high in fat.

  • Select foods that help achieve and maintain a healthy weight.

In addition, the National Cancer Institute (NCI) recommends that people limit their salt intake and increase fiber consumption.

Individuals who undergo cancer treatment often experience dietary problems, particularly when they are receiving chemotherapy. Maintaining adequate nutrition can be a challenge for these patients and malnutrition is a common problem. Treatments can reduce the patient’s appetite and can affect the body’s ability to tolerate certain foods. They also can impair the absorption of essential nutrients and cause side effects that make eating difficult or painful. Cancer patients must have a healthy diet to help them maintain their strength and energy to fight their disease.

The most common nutritional problem facing cancer patients is not consuming enough calories and protein. Nutritional needs depend on factors such as the patient’s size and age, and whether they have experienced significant weight loss because of treatment. Patients need to discuss their nutritional goals with their physician and/or dietitian. Eating well during cancer therapy can help individuals maintain their body weight, tolerate treatment-related side effects, reduce their risk of infection and provide other benefits.

Cancer patients who are unable to exercise proper nutrition because of treatment-related side effects, such as difficulty swallowing or nausea, may benefit from nutritional therapy. Nutritional therapy, which varies according to patient and treatment type, may include:

  • A specialized diet plan
  • Nutritional supplement beverages
  • Enteral nutrition (feeding tube inserted through nose or abdomen)
  • Parenteral nutrition (intravenous feeding tube)
  • Appetite-improving medications

Most treatment-related side effects disappear after treatment ends. Patients who continue to experience eating-related side effects should address their eating difficulties with their physician, nurse or dietitian.

About diet & cancer

Proper nutrition reduces the risk of numerous diseases, including certain cancers. According to the American Cancer Society (ACS), there is a direct link between dietary choices and 30 to 40 percent of cancers.

Good nutrition involves eating a variety of healthful foods – especially fruits and vegetables, which are rich in antioxidants. These nutrients protect the body against the tissue damage that results from normal metabolism. Because this tissue damage is linked to increased cancer risk, antioxidant nutrients may play an important role in cancer prevention.

Poor nutrition and inactivity typically contribute to excess body weight and obesity, which, in turn, increases an individual’s risk of developing many types of cancer. The National Cancer Institute (NCI) has extensively studied cancer development and its association with weight and physical activity. According to NCI’s 2005 Cancer Trends Update, an estimated 20 to 30 percent of some of the most common cancers in the United States may be linked to overweight and/or physical inactivity. In addition, studies have indicated that being overweight and obese may increase the risk of death of many cancers. These factors may account for up to 14 percent of cancer deaths in men and 20 percent in women.

The relationship between obesity and cancer is not yet fully understood. However, studies have shown that obesity increases an individual’s risk of developing the following types of cancer:

  • Breast cancer (in postmenopausal women)
  • Colorectal cancer
  • Endometrial cancer
  • Esophageal cancer
  • Gallbladder cancer
  • Kidney cancer
  • Pancreatic cancer
  • Prostate cancer

In addition, obesity may contribute to a greater risk of recurrence of certain cancers after treatment.

Scientists suspect that poor nutrition may increase the risk of other cancers as well, and that good nutrition may limit the risk. Many research studies are investigating the possible links between diet and the following cancers:

  • Bladder cancer
  • Lung cancer
  • Ovarian cancer
  • Stomach cancer
  • Secondary cancers

Studies of particular foods and their associations with cancer risks are ongoing. For example, research has suggested that a diet high in red meat may increase the risk of colon cancer and prostate cancer. In contrast, research has found that diets that are high in fruits and vegetables may lower the risk of lung and breast cancer. Scientists continue to examine these foods as well as other dietary factors to determine their effect on cancer development.

There are several common misconceptions about diet and cancer risk. For instance, many people believe that aspartame, a low-calorie sugar substitute, causes cancer in humans. However, no evidence suggests a link between the artificial sweetener and elevated cancer risk. There is also no evidence that the following foods and substances increase cancer risk:

  • Bioengineered foods. Foods that are genetically altered or modified to achieve various benefits (e.g., improved flavor, better resistance to pests).
  • Coffee
  • Fluorides
  • Food additives
  • Irradiated foods. Foods treated with radiation to eliminate harmful organisms.
  • Phytochemicals. A group of plant compounds.
  • Saccharin. An artificial sweetener.
  • Salt

Eating a balanced diet that is rich in nutrients is especially important for people with cancer. Consuming insufficient calories and protein is the most common nutrition problem that many cancer patients face, according to the NCI. There is no proof that eating well can slow, cure or prevent the recurrence of cancer. However, cancer patients typically benefit from additional nutrients that can help their bodies more effectively combat the disease and recover from the effects of treatment.

Role of diet in prevention

Eating a diet low in fat and high in fiber can reduce the risk of various diseases, including certain cancers. Many studies have suggested that specific nutrients can help prevent cancer. For example, lycopene (a pigment found in red fruits) and the mineral selenium may play a role in averting prostate cancer, according to the American Cancer Society (ACS). Other vitamins and minerals such as calcium and vitamin D are being studied continually for their role in cancer prevention as well. Because most research into diet and cancer is preliminary, the ACS recommends that individuals consume a variety of healthful foods – especially those derived from plant sources, which are packed with vitamins and fiber.

Dietary guidelines for cancer prevention include the following:

  • Eat at least five servings of fruits and vegetables each day. These foods are rich in antioxidant nutrients, which are believed to protect against cancer. Suggestions to achieve this guideline include:
    • Consume a variety of fruits and vegetables.
    • Include fruits and vegetables at every meal.
    • Replace unhealthy snacks with fruits and vegetables.
    • Prepare vegetables in a healthy manner (e.g., limit consumption of fried potato chips and french fries).
    • Drink only 100 percent fruit or vegetable juice.
  • Choose whole grains instead of refined (processed) grains and sugars.
    • Select whole-grain breads, pasta, rice and cereals.
    • Limit consumption of carbohydrates that are refined, including white bread, soft drinks, sweetened cereals, pastries and sugars.
  • Limit consumption of red meat, especially processed meats and those high in fat.
    • Replace beef, lamb or pork with poultry, fish or beans.
    • Select lean cuts of meat.
    • Consume smaller portions of meat (less than 3 ounces a day).
    • Prepare meat by baking, poaching or broiling instead of charbroiling or frying.
  • Select foods that help achieve and maintain a healthy weight.
    • Choose foods low in calories, fat and sugar when dining out.
    • Avoid oversized portions, especially when dining out.
    • Consume smaller portions of foods that are high in calories. Individuals should be aware that foods labeled “low fat” or “fat free” often contain many calories.
    • Replace calorie-dense foods, such as pizza, cheeseburgers and ice cream, with fruits, vegetables and other low-calorie items.
    • Limit the consumption of alcoholic beverages (one drink per day for women, two for men). The relationship between alcohol and cancer is not yet fully understood. Experts theorize that alcohol itself, or the way it is metabolized in the body, may have a carcinogenic effect. In addition, alcohol may increase certain hormone levels which are associated with a higher cancer risk.

Additionally, the National Cancer Institute (NCI) recommends that individuals limit salt intake and consume 35 grams of fiber a day. Fiber is found primarily in fruits, vegetables, whole grains and legumes. It helps prevent colorectal cancer, promotes weight loss, reduces cholesterol levels and offers other health benefits.

People often underestimate the portion size of healthy foods. Examples of a single serving include:

  • Fruits:
    • One medium apple, banana or orange
    • 1/2 cup (0.12 liter) of chopped, canned or cooked fruit
    • 3/4 cup (0.18 liter) of fruit juice with no added sugar
  • Vegetables:
    • One cup (1/4 liter) of leafy vegetables (raw)
    • 1/2 cup of other chopped vegetables (raw or cooked)
    • 3/4 cup of vegetable juice with no added sugar
  • Grains:
    • 1 ounce (28 grams) of cereal (cold)
    • 1/2 cup of cereal (cooked), pasta or rice
    • One slice of bread
  • Beans/nuts:
    • 1/2 cup of dry beans (cooked)
    • 2 tablespoons of peanut butter
    • 1/3 cup (0.08 liter) of nuts
  • Dairy/eggs:
    • One cup of yogurt or milk
    • One egg
    • 1-1/2 ounces (43 grams) of cheese (natural)
    • 2 ounces (57 grams) of cheese (processed)
  • Meats:
    • 2 to 3 ounces (57 to 85 grams) of lean poultry, fish or meat (cooked)

Role of diet in treatment

Exercising proper nutrition is especially important for cancer patients. Many cancer patients have a decreased appetite and cannot tolerate certain foods. This can result in poorer intake and less nutritional support. In addition, cancer can impair the body’s absorption of important nutrients (malabsorption).

According to The National Cancer Institute (NCI), many cancer patients have already experienced weight loss by the time their cancer has been diagnosed. This is particularly true for patients with gastrointestinal cancers and lung cancer. Loss of appetite or a decreased desire to eat is present in 15 to 25 percent of all cancer patients. This may be due to the cancer itself or as a side effect of treatments.

The various cancer treatments can also cause certain side effects that make eating difficult or painful. These side effects include:

  • Sore or dry throat and mouth
  • Gum or dental problems
  • Difficulty swallowing (dysphagia)
  • Change in taste or smell
  • Nausea or vomiting
  • Diarrhea and constipation
  • Fatigue
  • Depression

The type and severity of side effects depends upon a variety of factors including the type of cancer, the type of treatment, the length of treatment as well as other factors. Patients should speak with their physicians about the eating-related side effects of specific treatments and ways to counteract these problems. For example, if a patient has trouble swallowing, the physician may recommend adding liquids that are thick in consistency, such as milkshakes, or soft foods such as mashed potatoes to the diet.

If the patient often experiences nausea and/or vomiting, the physician may recommend adjusting the meal schedule to include longer periods between eating and treatment sessions, or smaller, more frequent meals. Changing the patient’s diet and antinausea medications also may help reduce these side effects.

The nutritional needs of people with cancer vary from patient to patient, and depend on factors such as the patient’s size and age, and whether an individual has experienced significant weight loss (5 percent of total body weight or more) due to treatment. Patients should discuss their nutritional goals with their physician and/or dietitian. Eating well during cancer therapy can help patients:

  • Feel better
  • Maintain their strength and energy
  • Maintain their body weight
  • Maintain their body’s store of essential nutrients
  • Tolerate treatment and its side effects
  • Decrease their risk of infection

Proper nutrition may also speed up the healing and recovery time of some patients. Eating well may even help some individuals handle higher doses of certain cancer treatments. In addition, cancer patients who are well-nourished typically have a better prognosis (predicted outcome for survival).

For cancer patients, eating well means consuming a variety of foods that provide the nutrients needed to help maintain their health while battling cancer. These essential nutrients include:

  • Protein. Protein helps to repair body tissue, maintain the immune system’s health and ensure growth. With insufficient protein, the body’s resistance to infection is reduced and recovery from illness may take longer. Therefore, cancer patients may require more protein than those without cancer. After surgery, radiation therapy or chemotherapy, extra protein is typically needed to mend tissues and help prevent infection. Good sources of protein include:

    • Lean meat and poultry
    • Fish
    • Low-fat dairy products
    • Nuts
    • Dried beans, lentils and peas
    • Soy foods
    • Egg whites

  • Carbohydrates and fats. These nutrients supply the body with the majority of its caloric needs. The amount of calories a person needs depends on size, age and level of physical activity. Sources of carbohydrates include:

    • Fruits
    • Vegetables
    • Pasta and breads
    • Grains and cereals
    • Dried beans, lentils and peas

    Sources of fat include:

    • Seeds and nuts
    • Butter, margarine and oils
    • Cheeses and other fatty dairy products
    • The fat in poultry, fish and meats
    • Egg yolks

The U.S. Department of Agriculture’s (USDA) revised food pyramid (now known as My Pyramid) suggests limiting consumption of fats and oils. In addition, fish oils and some vegetable oils, such as olive oil, have health benefits. The USDA recommends avoiding artery-clogging trans fats (such as partially hydrogenated vegetable shortening), saturated fats and cholesterol.

  • Vitamins and minerals. These nutrients are the basics for proper growth and development. They also enable the body to use the energy (calories) supplied in foods. Individuals who eat a balanced diet with sufficient calories and protein typically get enough vitamins and minerals. However, some side effects of cancer treatment can make eating a balanced diet very challenging. Therefore, physicians may recommend that patients who are undergoing cancer treatment take a daily multivitamin and mineral supplement.

  • Water. Water and other fluids are essential to good health. Individuals who do not consume enough water, or lose water due to vomiting or diarrhea, can become dehydrated. Patients should ask their physician or dietitian how many ounces of water they should consume daily.

In general, cancer patients should strive to consume the following each day:

  • Six servings of grains, preferably whole (unrefined)
  • Three to five servings of vegetables
  • Two to four servings of fruit
  • Eight 8-ounce glasses of water

Many cancer patients seek nutritional support prior to beginning cancer treatment. Early nutrition screening and assessment can help to identify any problems that may impact the success of cancer therapy. Early discovery and treatment of nutrition problems may help a patient maintain a healthy weight and reduce some of the complications from treatment. Patients who are otherwise healthy typically respond better to cancer therapy.

The patient’s cancer care team can play a vital role in maintaining adequate nutrition. The team usually includes a medical oncologist, oncology nurses and a social worker. Depending on the type of cancer, it may include a radiation oncologist, surgeon, psychologist and dietitian. Working together, the team can help the patient maintain the best nutritional status as possible.

Cancer patients who are unable to eat well because of treatment-related side effects may benefit from nutritional therapy. Nutritional therapy is designed to help patients in active treatment and recovery as well as those with advanced cancer. Goals of nutritional therapy may include preventing/correcting malnutrition, decreasing nutrition-related side effects, improving the patient’s quality of life. Nutritional therapy varies according to patient and treatment type, but may include:

  • A specialized diet plan
  • Nutritional supplement beverages
  • Enteral nutrition (a short-term feeding tube inserted through the nose, down the throat and into the stomach, or a long-term tube surgically placed through the abdomen into the stomach or small intestine)
  • Parenteral nutrition (an intravenous feeding tube)
  • Appetite-improving medications

Role of diet after treatment

Cancer treatments can produce a variety of eating-related complications that can affect nutrition. Many of the side effects disappear after a cancer treatment ends. However, some patients continue to experience difficulties after therapy has concluded. Eating well can help cancer patients regain strength and rebuild tissue. It can also foster feelings of general well-being. Therefore, patients with problems are encouraged to address their eating difficulties with their physician, nurse or dietitian. If the eating problem is due to psychological factors, such as depression, the patient may benefit from medication or mental health counseling.

Questions for your doctor on diet and cancer

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about diet and cancer:

  1. How will cancer and treatment affect my nutritional status?
  2. Am I likely to lose weight during treatments?
  3. What will be done if I cannot eat enough food?
  4. Will this cancer likely cause swallowing problems?
  5. Can medications help my appetite or nausea?
  6. How will my nutritional status be monitored through treatment?
  7. What supplements can I use if I do not eat enough?
  8. At what point will you consider a feeding tube?
  9. What are the differences among the feeding tubes?
  10. What can I do if I have frequent vomiting or diarrhea to stay hydrated?
  11. How will I know if I am dehydrated?
  12. Are certain foods easier to tolerate during cancer treatment?
  13. Can someone design a diet plan for me, if necessary?
  14. Can you recommend a dietitian?
  15. Should I take extra vitamins or supplements?
  16. Will my problems with eating stop after treatment?
  17. When can I expect to gain back lost weight?
  18. Does my current diet place me at higher risk for cancer?
  19. What changes should I make to help prevent cancer?
  20. Can diet changes reduce the risk of cancer recurrence?
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