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Questions and Answers About Cancer, Diet and Fats

October 01, 2007

Research is evolving about the relationship of diet to cancer. Cancer is a very complex disease, having few definitive answers regarding its cause. Factors to be considered include:

  • There are well over 100 different types of cancers, with many differing causes.
  • The average diet contains a tremendous amount of different components, some of which may lower the risk of cancer, while others may raise it.
  • Unlike heart disease in which blood cholesterol levels serve as an indicator of risk, there are no similar types of markers to indicate a cancer may be developing.
  • Cancer takes a long time to develop, which makes it difficult to establish a cause-and-effect relationship.
  • Research published in peer-reviewed journals is the most reliable source of emerging information about diet and cancer. However, because of the many questions about diet and cancer that remain unanswered, dietary recommendations should be based on the body of scientific evidence, not just one study.

What can be done to help reduce my risk for developing cancer?
More than 100 types of cancers exist with as many different causes which are not yet completely understood. The National Cancer Institute estimates that at least 35 percent of all cancers have a nutrition connection. There is no sure way to prevent cancer; however, health experts agree there is one general approach to take to help reduce your risk for developing cancer: manage your weight, adopt a healthy lifestyle that includes getting regular physical activity, eating a balanced diet, and not smoking. A healthy lifestyle plays a major role in determining cancer risk. When lifestyle factors such as smoking and exercise have been included, the associated risk becomes much stronger and may be as high as 85 percent.

How does diet affect cancer risk?
Several dietary factors appear to affect the risk of cancer. The type of food is one factor. Diets rich in plant foods such as whole grains, vegetables, fruits and beans may reduce risk for some types of cancer such as breast, oral, stomach, and esophageal. In addition, some studies have linked a diet high in animal products such as red meat with an increase in cancers of the colon and prostate.

Obesity is another risk factor for cancer that is affected by diet. Consuming more calories than you need can lead to obesity. Physical activity not only helps reduce risk for obesity, it also independently helps reduce the risk of developing certain cancers.

What is the most important dietary step to help reduce risk of cancer?
The strongest evidence points to a well-balanced diet high in whole grains, vegetables, fruits, and beans. These foods contain fiber, which is believed to reduce the risk of getting certain cancers. Although the association between fiber and cancer risk is weak, the consumption of these foods is still recommended due to other nutrients that my help to reduce the risk of cancer and have other health benefits.

What role does dietary fat play in cancer risk?
The role of dietary fat in the development of cancer, if any, is still unclear. Epidemiological research, which can only propose but not prove associations, suggests high-fat diets may increase risk for some cancers in some people. But other influences, such as that people who eat high-fat diets tend to be heavier and eat more calories and fewer fruits and vegetables, may play a greater role in the development of cancer.

According to the 2006 Dietary Guidelines of the American Cancer Society, high-fat diets have been associated with the development of colon, rectal, and prostate cancers. However, increasing consumption of whole grains, vegetables, fruits, beans, and other fiber-containing foods seems to be more important than decreasing fat intake to reduce the risk of cancers that have been associated with a high-fat diet. There is evidence that a diet high in saturated fat may have an increased cancer risk. More research is needed to determine clearly whether fat plays a direct role in the development of these cancers.

Diets high in fat have not been shown to be a factor in cancers of the stomach, kidney, esophagus, and larynx.

Does fat intake affect risk of breast cancer?
Scientists are still trying to determine if dietary fat plays a role in breast cancer. Breast cancer is associated with circulating hormone levels throughout life, which are influenced by several factors including obesity and physical activity. A recent study of 3,088 women in the United States found only no significant association between diets high in dietary fat and breast cancer. To lower risk of breast cancer, the American Cancer Society advises women to eat a diet rich in fruits and vegetables, be physically active, avoid obesity, and limit intake of alcoholic beverages.

Do the individual types of fats affect cancer risk?
The relationship of types of fat to cancer risk is being actively investigated, but it is not yet clear how saturated, monounsaturated or polyunsaturated fatty acids may affect cancer risk. Although several animal studies suggest polyunsaturated fats may increase tumor growth, no relationship has been found between polyunsaturated fats and cancer in humans. Likewise, studies in animals have found that omega-3 fatty acids suppress cancer formation, but there is no direct evidence for protective effects in humans at this time. The most recent review of the literature on trans fats and cancer concluded that there is no evidence that the intake of trans fats affects risk for cancer.

What advice do health experts give for cancer prevention?
Health experts advise a total approach to cancer prevention that includes getting enough physical activity, eating a healthful diet, and not smoking.

The recommendations to help prevent chronic disease, including cancer, are embodied in the Dietary Guidelines for Americans, which are tenets for an overall healthful lifestyle for all:

  • Adequate Nutrients within Calorie Needs. To make sure you get all of the nutrients and other substances needed for health, consume a variety of nutrient-dense foods and beverages within and among the basic food groups.  Choose the recommended number of daily amounts from each of the major food groups while including physical activity as displayed in MyPyramid.
  • Balance the food you eat with physical activity—maintain or improve your weight. Engage in regular physical activity and reduce sedentary activities to promote health, psychological well-being, and a healthy body weight.
  • Choose a diet moderate in total fat and keep saturated fat, trans fat, and cholesterol as low as possible.  Some dietary fat is needed for good health. Consume less than 10 percent of calories from saturated fatty acids and less than 300 mg/day of cholesterol, and keep trans fatty acid consumption as low as possible. The Nutrition Facts label helps you choose foods lower in saturated fat, trans fat and cholesterol.
  • Weight Management. To maintain a healthy body weight, balance calories from foods and beverages with calories used.  To prevent gradual weight gain over time, make small decreases in food and beverage calories and increase physical activity.
  • Choose a diet with plenty of grain products, vegetables and fruits, and moderate in sugar content. Choose fiber-rich foods such as fruits, vegetables, and whole grains often.  Choose and prepare foods and beverages with little added sugars or caloric sweeteners, such as amounts suggested by the USDA Food Guide and the DASH Eating Plan.
  • Choose a diet low in salt and sodium. Read the Nutrition Facts label to compare and help identify foods lower in sodium within each group. Use herbs and spices to flavor food. Try to choose form of foods that you frequently consume that are lower in sodium and salt.
  • If you drink alcoholic beverages, do so in moderation. If you drink alcoholic beverages, do so in moderation, with meals, and when consumption does not put you or others at risk.
  • Maintain a safe food environment.  Always practice safe food handling practices while preparing foods. Keep foods at proper temperatures and store foods immediately to prevent food borne illness. 

    References
  • American Cancer Society Guidelines on Nutrition and Physical Activity for Cancer Prevention: Reducing the Risk of Cancer With Healthy Food Choices and Physical Activity, Atlanta, GA: The American Cancer Society, 2006.

    Kushi L and Giovannucci E..  Dietary Fat and Cancer. The American Journal of Medicine.  2002 Dec 30;113 Suppl 9B:63S-70S.

    Pierce JP et al. Influence of a diet very high in vegetables, fruit, and fiber and low in fat on prognosis following treatment for breast cancer: the Women's Healthy Eating and Living (WHEL) randomized trial. JAMA 2007 Jul 18;298(3):289-98.

    U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2005 6th edition Washington, DC: U.S. Government Printing Office, January 2005.

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