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Harvard Commentaries
Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School

Food for Thought Food for Thought

Preventing Cancer Is More Possible Than You Think

January 16, 2013

By Hillary M. Wright, M.Ed., R.D., L.D.N.
Brigham and Women's Hospital

A recent survey by the American Institute for Cancer Research (AICR) found nearly half of Americans think that preventing cancer is either impossible or highly unlikely. This is despite the belief that cancer is our number one health concern. The survey also found that Americans' awareness of several proven links between diet and cancer remains alarmingly low.
  • Only 49% were aware that diets low in fruits and vegetables increase cancer risk.
  • Only 46% cited obesity as a risk factor for cancer.
  • Only 37% knew of alcohol's link to cancer.
  • Only 36% were aware of the link between diets high in red meat — particularly processed meat — and cancer.

At the same time, Americans are increasingly likely to attribute cancer to factors that lack a proven link to the disease. For example:

  • 71% view pesticide residue on produce as a carcinogen.
  • 58% see food additives as causing cancer.

Despite these misconceptions, the truth is we have a lot more control over our cancer risk than we think. According to a new international report from the AICR and their European counterpart, the World Cancer Research Fund (WCRF), about one third of cancers worldwide could be avoided through diet and activity.

Report Recommendations
  • Be as lean as possible within your normal body weight range.
  • Be physically active as part of everyday life.
  • Limit amount of calorie-dense food you eat ( those high in fat and sugar) and avoid sugary drinks.
  • Eat mostly foods of plant origin – fruits, vegetables and whole grains.
  • Limit intake of red meat (beef, pork and lamb) and avoid processed meats, such as bacon, sausage, bologna, ham and salami.
  • Limit your intake of alcoholic beverages.
  • Limit your salt intake.
  • Aim to meet your nutritional needs through diet alone.
  • Mothers should breastfeed their babies as it lowers the risk of breast cancer and reduces their child's risk of obesity later in life.
  • Cancer survivors should be encouraged to follow the report's recommendations for cancer prevention, and seek the advice of a trained nutrition professional.

The report, called Food, Nutrition, Physical Activity and the Prevention of Cancer: A Global Perspective, took five years to complete and was based on more than 7,000 scientific studies. It is the most comprehensive review ever published of the science linking cancer risk to diet, physical activity and weight.

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Convincing Evidence

The Report found convincing evidence for a link between cancer and the following lifestyle practices:

  • Excess weight — especially abdominal fat. Since the 1990's more and more research has supported a connection between excess weight and numerous cancers. Being overweight increases the risk of post-menopausal breast cancer, and cancers of the colon, pancreas, kidney, endometrium and esophagus. In fact, excess weight is now second only to cigarette smoking as a preventable cause of cancer. How excess weight increases cancer risk is complex, but the evidence points to numerous cancer-promoting hormones and other factors that are raised in those who are obese. Main Message: Pay attention to weight beginning in childhood and avoid weight gain as you age.


  • Physical activity. All forms of activity can protect against colon cancer, and probably protect against post-menopausal breast cancer and endometrial cancer. Active people have healthier levels of circulating hormones, and may be able to eat more without gaining weight. Main Message: Start with 30 minutes of moderate activity daily, and work up to 60 minutes of moderate activity (or 30 minutes of vigorous exercise). Limit sedentary habits like television watching, which is often accompanied by mindless munching on high-calorie snacks.


  • Red meat — particularly processed meats. We have stronger evidence now than in 1997 (when the report was last compiled) that high intakes of red and processed meats – those preserved with smoking, curing or salt – increase the risk of colorectal cancer. Main Message: Eat no more than 18 ounces of meat per week; very little, if any, should come from processed sources.


  • Alcohol. Even moderate alcohol intake may increase risk of cancers of the head and neck, esophagus, colorectum (in men) and breast. It also is considered a probably cause of liver cancer and colorectal cancer in women. But it may also reduce the risk of heart disease. Main Message: Limit alcohol to no more than two drinks a day for men, and one drink a day for women. One drink is a 12 ounce beer, five ounces of wine or 1.5 ounces of spirits.

Probable Evidence

  • Plant foods. The Report strongly encourages eating mostly plant foods due to their "probable" protective effect against cancers of the digestive tract, lung and prostate, and known connection to successful weight loss. Main Message: Fruits, vegetables and whole grains are low in calories, good sources of fiber and contain thousands of health-promoting chemicals that likely contribute to their cancer-fighting effect.

What About Dietary Supplements?

Although taking dietary supplements may be useful for other health reasons, the research to date doesn't support that they'll lower your cancer risk. In fact, beta carotene supplements raise lung cancer risk while other supplements may lower cancer risk.

What are Your "Best Bets" for Staying Cancer-Free?

  • Make weight loss a priority by watching portions, avoiding sugary drinks and significantly limiting "fast foods" and other foods high in fat and sugar.


  • Aim for at least 5 servings of fruits and vegetables daily.


  • Aim for 30 minutes of activity daily — either at once or in short bouts — with a long-term goal of 60 minutes of activity most days.


  • Limit red meat to 18 ounces or less per week, and avoid processed meats.


  • If consumed at all, drink alcohol in moderation.

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Hillary M. Wright, M.Ed., R.D., L.D.N. is a Senior Nutritionist for the Dana Farber/Brigham and Women's Cancer Care Program. Hillary also has a private nutrition counseling practice specializing in women's health and is a writer and contributing editor for the newsletter Environmental Nutrition.

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