Written by Ruth MacDonald, R.D., Ph.D.
Cancer is a frightening disease that affects the lives of millions worldwide. Many of us know someone personally who has struggled with cancer or has lost a loved one to this disease – or have suffered from it ourselves.
The good news is that recent National Cancer Institute statistics show a reduction in the incidence of cancer in the United States. This may be due in part to earlier detection and better screening for cancers, or perhaps it reflects a reduction in the number of people who smoke cigarettes. Cancer is a complex disease that can occur in almost all types of cells in our body, and there is no single cause of cancer. Some factors, such as cigarette smoking, have clear links to cancer. Other strongly linked factors include exposure to radiation (including sunlight), and environmental chemicals and pollutants. For centuries, foods have been linked to cancer, in both promotion and protective capacities. More recently, we are learning that physical activity and maintaining a healthy weight are also closely linked to reducing cancer risk.
All foods, from fruits and vegetables to processed cheese and cookies, are complex mixtures of many chemicals. Foods contain known nutrients like carbohydrates, fats, proteins, vitamins and minerals; but also thousands of other chemicals such as polyphenols, tannins, catechins, sterols and flavonols. Hence, to understand the role of foods in cancer, we must understand the chemical composition of foods and the roles of these specific chemicals in the cancer process. This is a daunting task and one that may never be fully completed because of the number of chemicals and the multitude of possible interactions in a normal diet.
There are several ways to study the associations between foods and cancer. One way is to compare cancer incidence in populations with the foods they consume. This type of epidemiological study provides correlations but cannot prove cause and effect, but it does allow scientists to identify which dietary factors may be most important for further study. Over the past 50 years, many studies have been conducted to clarify the role of foods and ingredients in cancer. Some of these have been popularized in the lay press and have been promoted in the grocery store. For example, higher intakes of dietary fiber were correlated with lower risk of colon cancer. As a result of this finding, food manufacturers rushed to increase the fiber content of foods and promoted high fiber diets to reduce colon cancer risk. Subsequent large human clinical trials, however, have been ambiguous about the protective effects of fiber in colon cancer.
Another dietary component thought to play a significant role in cancer is dietary fat. Some studies found a higher incidence of breast and colon cancer in populations that consumed high amounts of fat. Many studies were done to identify the specific types of fat and the mechanisms through which these components may impact cancer risk, but as with fiber, large human studies of dietary fat related to cancer have not shown a clear relationship. This is frustrating to consumers, but reflects the complexity of the disease, the diet, and the interactions between the two that occur in the human body. As we develop better molecular tools, it is likely that we will be able to clarify which genetic factors influence the response to dietary components in individuals. While we wait for science to reach this point, diets high in fiber and low in fat may have many positive health benefits and continue to be recommended to reduce cancer risk.
Food ingredients, including flavors, colors, preservatives and artificial sweeteners, have been widely publicized as cancer-causing. These concerns are largely unfounded. The FDA has stringent requirements to demonstrate safety before any component is added to the nation’s food supply. While we may never be fully sure that a chemical will never cause cancer given the right environment in a specific individual, the U.S. food supply is very safe. However, we may not assume that the food supply is free of carcinogens, because some edible plants contain naturally occurring mutagenic compounds and environmental pollutants do contaminate plant and animal foods. In general, these are in very low concentrations.
To reduce the risk of exposure to these compounds, one should consume a wide variety of foods from reputable sources.
The American Institute for Cancer Research has undertaken an extensive evaluation of the scientific research of the relationships among foods and cancer. They have identified the following foods as being helpful in reducing the risk of the main forms of cancer in the United States, to include breast, prostate and colon cancers. These foods should be part of one’s everyday diet, because they are rich in vitamins, minerals, fiber and many beneficial compounds such as polyphenols, flavonoids and catechins, which have a variety of positive effects on the body.
- Citrus fruits, grapes and berries
- Cruciferous vegetables (broccoli, cauliflower)
- Dark green leafy vegetables (spinach, kale)
- Colorful vegetables (tomatoes, squash, pumpkin)
- Whole grains
- Fish and flaxseed
- Dairy foods (yogurt, skim milk)
- Nuts (walnuts, almonds)
- Green and black tea
While a healthy diet is critically important to lowering cancer risk, many other lifestyle features are also important. Here are ways to improve overall health and protect yourself from cancer:
- Avoid smoked, salted or burnt meats.
- Seek a balanced diet, adequate in protein, fat and carbohydrates.
- Maintain a healthy weight.
- Perform regular exercise.
- Avoid sugary drinks and high-fat foods.
- Get routine screenings and checkups.
- Don’t smoke.
- Get enough sleep.
- Use household and farm chemicals properly.
- Enjoy life and manage stress.
View the full spring 2009 issue of the ACSM Fit Society® Page online.