Many people have a fear of cancer, perhaps because to them it is always an incurable disease. The facts do not support this idea.
Countless numbers of Americans who are alive today have had cancer and are now considered to be cured. ("Cured" is defined here as being free of any evidence of the disease for 5 years or more.) They may have the same life expectancy as others of the same age and sex who have never had cancer, and they can anticipate leading meaningful and productive lives.
Despite such impressive statistics, cancer remains a serious disease. Annually, cancer is diagnosed in more than a million people (excluding non-melanoma skin cancer) and is one of the most significant causes of mortality in the United States.
There are more than 100 different types of cancer. Some cancers affect just one organ, and others are more generalized. In each of its types, however, cancer is characterized by the uncontrolled growth and spread of abnormal cells (see illustration on page 74).
Why cancer develops in some people who are exposed to potentially cancer-causing agents but not in others is not fully understood. But what is known is that many cancers develop slowly. It may be 5 to 40 years after exposure to a cancer-causing agent before there is any evidence of the disease. Cancer of the lung, for example, may not appear until 25 years or more after sustained exposure to tobacco smoke. This long delay between exposure and development of the disease may partly explain why so many people ignore the warnings associated with smoking.
Cancer Terms—Ancient and Modern
Cancer is a disease we have known about since ancient times. The terms used to describe cancer come from ancient languages.
"Cancer" is derived from a Latin word meaning "crab" and was first described in writings attributed to Hippocrates and other Greek physicians (500 B.C. to 200 A.D.). These physicians described various tumors and classified them as either "carcinos" (benign growths that do not spread) or as "carcinomas" or "crab-like" (growths that invade surrounding tissues and cause death). The term "neoplasm" was described by Galen (200 A.D.) as meaning "new growth that is contrary to nature." The word "metastasis" is also a Greek word meaning "to change places." It is used to describe the ability of cancer to migrate to other tissues or organs and to form additional tumors.
The Nutrition-Cancer Connection
During the past 30 years, research has shown that nutrition plays a significant role in the development of many cancers and that proper food choices might help to reduce the risk of cancer or even prevent it. About a third of the 500,000 cancer deaths that occur each year in the United States can be attributed to dietary factors. The good news is that in addition to engaging in regular exercise and not smoking, people have control over this important factor in cancer development—their food choices.
Any number of dietary factors may be related to the risk of cancer.
The Biology of Cancer
A biomedical revolution is advancing knowledge of the causes of cancer, yielding new and more effective treatments and inspiring greater hope for cancer prevention. This revolution is built on scientific investigation of the basic processes that cause cancer.
The body is a living, growing system that contains billions of individual cells. These cells carry out all of the body’s functions, such as metabolism, transportation, excretion, reproduction, and locomotion. The body grows and develops as a result of increases in numbers of new cells and their changes into different types of tissue. New cells are created through the process of cell division (mitosis). Different types of cells are created by a process called cell differentiation, by which they acquire specialized function. Cell division results in the normal pattern of human growth; cell differentiation makes possible the normal, orderly pattern of growth and development.
Cancer cells, left untreated, invade and penetrate the walls of blood and lymph vessels. Once in these systems, they travel to other sites, such as the lungs, bone, or brain.
Unlike normal cells, cancer cells lack the control mechanisms that stop, or "switch off," growth. They divide without restraint, displacing neighboring normal cells, affecting their normal function and growth, and competing with them for available nutrients. These uncontrolled cells can grow into a mass called a tumor and invade and destroy nearby normal tissue. They also can migrate in a process called "metastasis," spreading via the blood or lymph system to other parts of the body. Not all cells that have rapid or uncontrolled growth are cancerous. Cells may amass as benign tumors, which do not invade or destroy surrounding tissues.
Although science has yet to understand the processes by which all cells grow, divide, communicate, and differentiate, much has been learned about how normal cells are activated or altered into cancerous cells in both inherited and non-inherited forms of cancer.
The Causes of Cancer
Cancer is caused by factors that are external (chemicals, radiation, viruses, and diet) and internal (hormones, immune and metabolic conditions, and inherited [genetic] alterations). Some of these factors are avoidable; others are not. Scientists have identified many of the controllable risk factors that increase the chances of getting cancer. A complex mix of these factors, acting together or in some cascade of events, promotes cancer cell growth.
When the genetic programming of a normal cell is disrupted, its malignant potential is released. Everyone carries this malignant potential within them in normal genes known as proto-oncogenes. Products of these genes perform useful functions, such as regulating cell division and cell differentiation. These functions, however, may be compromised with aging or by exposure to cancer-causing (carcinogenic) agents. When this happens, they may be activated to become oncogenes, coordinating the conversion of normal cells to cancer cells.
Nutrition can influence any of the steps involved in the development of cancer. The development of cancer (carcinogenesis) and its relationship to nutrition is a complex process. Isolating and proving dietary cause-and-effect relationships can be difficult. In addition, studies can be confusing and sometimes show conflicting results. Nevertheless, the potential for nutrition to increase or decrease the risk of various cancers is compelling.
Dietary Guidelines to Reduce the Risk of Cancer
Just as negative dietary and lifestyle choices can significantly increase the risk of cancer, evidence is mounting that appropriate food choices can be powerful tools in reducing risk and even defensive shields in preventing cancer. The American Cancer Society offers these four guidelines to reduce cancer risk:
• Choose most of the foods you eat from plant sources.
• Limit your intake of high-fat foods, particularly from animal sources.
• Be physically active: achieve and maintain a healthful weight .
• Limit consumption of alcoholic beverages, if you drink at all.
The Society’s recommendations are consistent with the U.S. Department of Agriculture Food Guide Pyramid and the Dietary Guidelines for Americans. Although no diet can guarantee full protection against disease, the American Cancer Society believes that these recommendations offer the best nutrition information currently available to help reduce your risk of cancer.
Choose Most of the Foods You Eat From Plant Sources
Choosing foods from plant sources is vital to a healthful diet. Many scientific studies have shown that increased consumption of fruits, vegetables, and whole grains reduces the risk for cancers of the gastrointestinal and respiratory tracts and for lung cancer. This reduction is one of the reasons foods of plant origin form the basis of the Food Guide Pyramid.
Plant foods contain beneficial vitamins, minerals, fibers, and hundreds of other cancer-protective substances. Although more research is needed to understand what specific properties or substances in plant foods may specifically protect against cancer, there are already many candidates under investigation—from vitamins and minerals to fiber and phytochemicals (including carotenoids, flavonoids, terpenes, sterols, indoles, and phenols). Because the positive effects from these components may derive from the whole foods in which they are found, experts recommend food over supplements.
Antioxidants found in fruits and vegetables may help to prevent cancer. These are nutrients that seem to offer the body some protection against oxidation—damage done to tissue in the course of normal cellular function which may contribute to the effects of aging and to increased cancer risk. Various antioxidant nutrients—including vitamin C, vitamin E, selenium, and carotenoids —may provide the body with some defense against cancer. Researchers are studying the protective role of antioxidants.
Grains provide vitamins and minerals, such as folate, calcium, and selenium, which may also protect against cancer. Whole grains are preferable to refined grains because they have more fiber and an abundance of certain vitamins and minerals. Beans and legumes are also good sources of nutrients that have cancer-protective qualities. (See page 20 for more information about fiber.)
Although more research is needed to clarify the specific roles of these food components, there is still ample evidence to support eating 5 or more servings of fruits and vegetables a day (especially deep-green and dark-yellow to orange fruits and vegetables, those from the cabbage family, and legumes and soy products) and 6 to 11 servings of grains (with an emphasis on whole grains).
Limit High-Fat Foods, Particularly From Animal Sources
Decreasing the intake of high-fat foods, especially from animal sources, is very important. Studies show that people who eat a high-fat diet have increased rates of cancers of the colon, rectum, prostate, and endometrium (lining of the uterus). Although these relationships exist, it is not clear whether they are due to the total amount of fat in the diet, to a particular kind of fat (saturated, monounsaturated, or polyunsaturated), or to another, unknown, factor.
Because fat, by weight, contains twice the number of calories than protein or carbohydrate, it is difficult to separate the effects of the fat from the effects of its calories. People who eat a high-fat diet are often heavier and tend to eat fewer fruits and vegetables, which also increases cancer risk.
Consumption of red meat, a major source of fat in the American diet, is linked to an increased cancer risk, particularly of the colon and prostate. Scientists are unable to determine whether the connection between red meat and cancer is due to total fat, saturated fat, or other compounds. Meat contains compounds linked to cancer, such as heterocyclic amines, which are produced when it is cooked (see sidebar: Meat—Cooking and Cancer, page 77). This may be a link to colon cancer.
Food versus Supplements
Every day there seems to be a headline announcing that some nutrient or food compound has been linked to preventing some sort ofcancer. Driving this is the tremendous amount of research exploring specific food components and their role in the cancer process.
Do supplements offer cancer protection?
A diet that contains ample amounts of fruits and vegetables is associated with a reduced risk for cancer. There is no evidence that mineral or vitamin supplements are better than obtaining nutrients through whole foods. In fact, studies in which subjects received supplements of beta-carotene showed conflicting and even harmful results. Smokers given supplemental beta-carotene had a higher incidence of lung cancer. Other studies of supplemental beta-carotene have shown neither benefit nor harm.
There are more than 500 known carotenoids. Of these, only a few have been analyzed: alpha-carotene, beta-carotene, gamma-carotene, lycopene, lutein, and zeaxanthin. At this time, it is not known which exerts benefits—or risks.
Experts recommend a diet rich in fruits, grains, and vegetables rather than taking supplements. Plants contain hundreds of cancer-protective substances. It is not known which of the substances may specifically protect against cancer. In addition, it is not known whether these substances work independently or benefit from working together. Plus, relying on supplements rather than eating a variety of foods makes it impossible to benefit from these now unknown food compounds.
Meat—Cooking and Cancer
Cooking meat at high temperatures creates chemicals that are not present in uncooked meats. Heterocyclic amines (HCAs) are chemicals linked to cancer that are formed when meat is exposed to high temperatures. Four factors influence HCA formation:
Type of food
HCA is found in cooked muscle meats. Other protein sources (milk, eggs, tofu, and organ meats such as liver) have little or no HCA naturally or when cooked.
Temperature
Cooking temperature is the most important factor in reducing the formation of HCA. Cooking in an oven at 400° Fahrenheit or less or stewing, boiling, or poaching at 212° Fahrenheit or less forms one-third of HCAs versus meats prepared by frying, broiling, or grilling.
Cooking method
Frying, broiling, and barbecuing produce the largest amounts of HCA—these methods have higher than recommended cooking temperatures. Microwaving meats for 2 minutes helps to decrease HCA. Meats that are microwaved before frying, broiling, or grilling have a 90 percent decrease in HCA content. Marinating meats before cooking also inhibits the production of HCA.
Time
Meats cooked well done (no pink remaining in center) have more HCA than those cooked medium.
Different fats (such as omega-3 fatty acids and vegetable oil) may have different effects on your risk of cancer. Saturated fat is a particular concern for cancer risk and for coronary artery disease.
How food is prepared is also important. Some cooking methods, such as baking, stewing, boiling, and poaching, are healthier ways than frying, broiling, or grilling.
Limit Consumption of Alcoholic Beverages
People who drink excessive amounts of alcohol have an increased risk of cancer, higher than that of the general population, especially cancer of the larynx, esophagus, stomach, and pancreas.
There is no question that limiting alcohol consumption reduces cancer risk. The risk of cancer begins to increase with an intake of as few as 2 drinks a day. Alcohol along with tobacco use produces a combined cancer risk that is greater than the sum of their individual effects. The risks for cancers of the mouth, throat, esophagus, and larynx are particularly increased.
Research also has noted a connection between alcohol consumption and an increased risk of breast cancer. Although the causes are not known, scientists speculate that alcohol may have a carcinogenic effect, perhaps reflected in its capacity to alter hormone levels.
Drinking too much alcohol also may negatively affect eating habits. The calories in alcohol—with little nutritional value—are perhaps being consumed in place of calories in healthier foods with cancer-protective values. A general rule: men should limit themselves to no more than 2 drinks a day, women to 1. (See page 387 for a further discussion about alcohol.)
