New United Nations Report Supports Key Role for Diet, Activity in Cancer Prevention

American Institute for Cancer Research
Monday, 3 March 2003

US Cancer Experts Welcome WHO Report's Championing of Dietary Factors

Cancer experts at the American Institute for Cancer Research (AICR) today applauded a new report from the United Nation's World Health Organization (WHO).

"This new document reflects the mountain of data linking diets rich in plant foods, notably vegetables, fruits and whole grains, to lower risk for cancer," said Ritva Butrum, Vice President for Research at AICR. "Until the 1990s, the idea that diet is crucial to the prevention of cancer was still considered unorthodox.

"Thousands of scientific studies later, this vital message has been heard around the world. We are delighted that today's World Health Organization report offers further confirmation of a simple truth that can help save millions of lives around the globe."

The new document, the scientific basis for WHO's new Global Strategy for Diet, Physical Activity and Health, is entitled Diet, Nutrition and the Prevention of Chronic Diseases.

The scope and format of the WHO report echo those of the 1997 AICR/WCRF Expert Panel Report, Food, Nutrition and the Prevention of Cancer: a global perspective. Unlike the WHO report, the earlier AICR/WCRF report exclusively examined the global evidence for a diet-cancer link, and was the first to do so using a methodical and comprehensive approach.

In fact, several aspects of the AICR/WCRF report were used in drafting the WHO document. Both reports stress the need to examine the role of diet using a global strategy. Both documents begin with a positive message by highlighting the tremendous preventive potential of diet and activity.

Like the AICR/WCRF report, the new WHO report classifies the current evidence for specific links between diet and disease into specific categories: convincing, probable, possible or insufficient.

However, the cancer experts at AICR were quick to point out important differences between the two documents that remain.

"Our 1997 Expert Panel Report looked at the global evidence using meta-analysis, a method that rigorously quantifies the strength of diet-cancer links in each study," said AICR's Butrum. "Doing so allows comparisons between different types of studies, and between studies that measure the same things in different ways. Our review panels were thus able to base their judgments on a uniform statistical standard."

By contrast, the new WHO report utilized a method called narrative review, in which experts select and comment upon studies using their personal best judgment; this is a simpler method but lacks precision and objectivity.

AICR experts maintain that, if WHO had evaluated the current research using a more thorough and consistent methodology, their report would have placed an even stronger emphasis on the importance of vegetables and fruits.

To date, literally thousands of studies consistently show correlations between fruit and vegetable consumption and lower cancer risk. The cancer experts at AICR also note that these studies used different methods to investigate different aspects of the diet-cancer link and yet reached similar conclusions. Taken together, this evidence amounts to proof of a causal relationship beyond any reasonable doubt. That's why AICR, and also the National Cancer Institute (NCI), continue to recommend daily consumption of 5 to 9 servings of vegetables and fruits.

Laboratory results, for example, continue to illustrate how components in these foods actively fight the cancer process. Studies that track the diets of individuals over many years consistently reveal lower cancer rates among those who consume more than five servings of vegetables and fruits per day.

Recently, the protective potential of these foods was corroborated in preliminary results from the pan-European EPIC study, the single largest ongoing study of diet and cancer risk ever undertaken.

Results from randomized clinical trials involving diet and cancer are less consistent than results from other kinds of studies. But clinical trials were not designed to study the complex role of multiple dietary influences on cancer risk over long periods of time, and are ill suited to the task. Because of their highly focused, short-term nature, such trials are more useful for studying the effects of specific cancer drugs upon cancer patients, not the ability of overall diet to prevent cancer in healthy individuals.

AICR and its umbrella organization WCRF International are currently at work on a comprehensive update and expansion of Food, Nutrition and the Prevention of Cancer: a global perspective. This massive project will require an unprecedented amount of data – nearly 20,000 individual studies – to be compiled and rigorously analyzed using an objective and replicable systematic methodology. Once completed, the expanded AICR/WCRF International report will represent the most comprehensive and definitive appraisal of the diet-cancer link possible.

"In the meantime," said Dr. Butrum, "today's best available science tells us what your grandmother always knew. Get a wide variety of vegetables and fruits, all year round'.

For more information, or to contact American Institute for Cancer Research, see their website at: www.aicr.org