‘One Third of Cancers Could Be Prevented by Diet’

WASHINGTON—In a 650-page report prepared collaboratively by the American Institute for Cancer Research and the World Cancer Research Fund, international cancer experts have established that approximately one-third of all cancers are preventable through dietary changes, combined with physical activity and maintenance of recommended body weight. Avoidance of tobacco and alcohol(Drug information on alcohol) could prevent another one-third of all cancers.

The potential for saving lives through good dietary habits is enormous. Of the approximately 600,000 cancer deaths in the United States each year, 200,000 might be prevented if the report’s dietary guidelines were widely followed. By the year 2020, when new cases of cancer worldwide are projected to reach 14.7 million a year, a potential 5 millon cases could be prevented each year.

The report, compiled by 16 medical and scientific professionals from around the world who specialize in oncology, nutrition, and public health, was presented at conferences in Washington, London, New Delhi, Brussels, and Tanzania.

The findings are the culmination of the panel’s 3-year review of more than 4,500 scientific studies on diet and cancer. It is the first analysis of its kind to focus on foods and diet as a whole rather than on individual compounds in foods.

The panel’s recommendations address specific issues about lifestyle, the foods we eat, and how that food is preserved and stored (see Table at right). The dietary principles outlined in the report are the same as those widely acknowledged to reduce the incidence of adult onset diabetes, hypertension, and cardiovascular disease.

Laurence N. Kolonel, MD, PhD, Deputy Director and Program Director for Cancer Etiology at Hawaii’s Cancer Research Center and a member of the expert panel, said in an interview that despite cultural differences, any population can build upon local food sources to incorporate the recommended guidelines into their cuisine and thus expect to achieve the 30% to 40% reduction rate.

He stressed that it is never too late to begin good dietary habits, since cancer is a multistep process that may be stopped at a preclinical stage. “The latency period of some cancers can be very long—20, 30, 40 years,” he said. “You might have initiated a cancer 15 years ago, but if you change now, you could still have a positive impact.”

He went on to caution that while multivitamins and supplements may have a place in the medical management of certain conditions, the general population has no need of these and, in fact, should not attempt to replace natural foods with supplements.

His major concern, he said, is that Americans, who “tend to think there’s a pill for everything,” may be tempted to neglect their diet in the belief that supplements will provide what they need. But he explained that they should not make that leap.

Beta-carotene is a case in point. First of all, he said, experts aren’t sure that it is beta-carotene by itself or in combination with other nutrients that has anticancer properties; but even if beta-carotene acts alone, it may be more effective when our bodies extract the nutrient from natural foods rather than from synthetic sources.

As Dr. Kolonel explained, pharmacologically manufactured nutrients may not match those found in nature; for example, during their preparation or storage, dietary supplements may have been subjected to seemingly innocuous influences such as artificial light, which can subtly alter their properties and render them ineffective.

Dr. Kolonel emphasized that there is, as yet, no definitive evidence that any single nutrient in foods or even that certain whole foods themselves, such as leafy green vegetables, confer greater protection than others. He stressed that eating a variety of foods, sensibly balancing one’s choices from the recommended categories, avoiding alcohol and tobacco, and making appropriate lifestyle changes to stay fit offer optimum benefits.

While the experts did not name fat as a single causative agent, Dr. Kolonel pointed out evidence that it can contribute to cancer development and should be limited to a maximum of 30% of calories, with a lower limit of 15%.

One problem, he said, is that many people believe eating fat-free foods lowers their calorie intake, but the additional calories they consume from the extra sugars that are often added to these foods still means the body has an excess of calories, which it will store as fat. To truly reduce fat intake and lose weight, people need to limit calories, regardless of which foods supply them.

Panel members have stated they expect the next step in implementing their recommendations globally will begin at the public policy and health education levels, ultimately filtering down to the public where real changes can be effected. Such implementation may have a greater chance of success with the publication of the report’s finding that diet and nutrition play a critical role in the rate of cancer incidence.

Their hope is that implementation of their recommendations could reverse the upward trend of cancer rates throughout the world. The panel feels that a realistic intermediate global target is a 10% to 20% reduction in cancer rates within 10 to 25 years.