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November 13, 2008   

Diet, nutrition and cancer: public media and scientific confusion

In the October 2008 issue of Annals of Oncology, P. Boyle and colleagues wrote an editorial questioning the responsibility of scientists and subsequently the media in presenting the facts of diet and cancer research in context. They indicate that secondary to tobacco, we know that diet and nutrition play a role in determining cancer risk. However, the evidence beyond that is unclear.

The World Cancer Research Fund report (WCRF), released in 2007, was used as an example. In 1997, high fat diets and low consumption of fruits and vegetables and fibres were associated with increased risks of common cancers. The low consumption of fruit and vegetable has subsequently been shown to lack consistent association with cancer risk. These inconsistencies cast doubt on the strength of evidence of supporting recommendations in reports such as the WCRF. The authors state, “in view of the fragile grounds on which the conclusions of the WCRF report on diet and cancer are based on, the information to the media should have been more cautious, which would probably have prevented confusion of messages disseminated to the public.”

Diet related research is very difficult to conduct with the multiple correlations and differences in individual behaviours. Epidemiologic studies take a long time and rely on food intake questionnaires and food composition tables which have limitations. Further epidemiologic studies suggest an association between variables not prove causation. The authors propose a need for research that identifies biomarkers of diet rather than relying on current methods.

We still do not know what to eat to decrease our risk of cancer. Systematic reviews give us hints but none provide the strength of evidence shown with the relationship between tobacco use and cancer risk, which is ten-fold stronger. Cancer is a complex set of diseases and giving the public food specific recommendations, simplifies the situation. As a result, media, and subsequently the public, need to be given the facts in context to avoid the confusion that exists between diet and cancer.

For your practice:

Keep research results in perspective – eliminating tobacco use and/or exposure is the most significant cancer risk reduction step. Healthy eating, following Eating Well with Canada’s Food Guide will provide many health benefits. However, eliminating or adding specific foods will unlikely have a substantial impact on cancer deaths.

For more information:

Boyle P, Boffetta P, Autier P. Diet, nutrition and cancer: public, media and scientific confusion. Annals of Oncology 2008; 19:1665-67.

Download Nutrition Perspective: Meat and Colorectal Cancer, 2007