Inherent problems found in dietary study
A new study in today's Archives of Internal Medicine tries to predict the future risk of death by relying on notoriously unreliable self reporting about what was eaten in the preceding five years. This imprecise approach is like relying on consumers' personal characterization of their driving habits in prior years in determining their likelihood of having an accident in the future.
Meat products are part of a healthy, balanced diet and studies show they actually provide a sense of satisfaction and fullness that can help with weight control. Proper body weight contributes to good health overall, said AMI Executive Vice President James H. Hodges. Meat is an excellent source of zinc, iron, B12 and other essential vitamins and minerals. The U.S. Dietary Guidelines say to eat a balanced diet that includes lean meat. In this way, you derive a wide array of nutrients from many different sources. It's the best return on a nutritional investment you can get.
Hodges added, Single studies cannot be used to draw major conclusions, yet that just what these authors seem to be doing by releasing this study with a major national press release.
In this new study, researchers asked people to recall what they ate over the previous 12 months and to record it into a 35-page, detailed questionnaire. Notably, the front page of the questionnaire says Answer each question as best you can. Estimate if you are not sure. A guess is better than leaving a blank. After 10 years and after receiving questionnaires only at the outset, the five year mark and the 10 year mark, the researchers tried to correlate dietary factors with deaths.
No doubt many participants guessed extensively in an effort to recall five years of habits and answer 35 pages of questions. Health conclusions and public policy recommendations should not be based on mere guesses, Hodges said.
Further, many papers including several recently published reached far different conclusions about the role of meat in the diet which the authors did not acknowledge in their discussion of their own interpretations of the study data:
- A paper published in the March 11 American Journal of Clinical Nutrition found that vegetarians had higher risk of colon cancer than meat eaters.
- A Harvard study involving 725,000 people that examined red and processed meat and colon cancer the largest of its kind on this topic concluded that there was no risk between the two (Cho, Smith-Warner, et. al., American Association for Cancer Research 2004 proceedings). Additionally, another report from the same research group, failed to find a protective effect of fruit and vegetables against colorectal cancer in this same population group. They concluded, "Fruit and vegetable intakes were not strongly associated with colon cancer risk overall but may be associated with a lower risk of distal colon cancer." (J Natl Cancer Inst 2007;99:1471¨C83).
- A new study which appears in this month's peer-reviewed Journal of Nutrition carried out by the University of Illinois and Pennsylvania State University tested the effect of diet and found that a moderate-protein diet can have a significant positive effect on body composition as well as on cardio-vascular disease risk factors such as cholesterol. Subjects on the moderate-protein diet reported that they weren't as interested in snacks or desserts, and they didn't have food cravings.
The authors' reference to a widely critiqued 2007 World Cancer Research Fund (WCRF) report and the suggestion that the latest study is consistent with it raises additional concerns.
The meat industry is not alone in its view of this report's inherent problems. In 2008, Peter Boyle, Ph.D., Phillippe Autier, M.D., and Paolo Boffetta, M.D., Ph.D., of the United Nations International Agency for Cancer Research (IARC) wrote a highly critical editorial in the Annals of Oncology. In it, they said, "The substantial review of the evidence in the WCRF report demonstrates that there is no discernible association between many forms of cancer and specific dietary practices¡the cupboard is remarkably bare... In view of the fragile grounds on which the conclusions of WCRF report on diet and cancer are based on, the information to the media should have been more cautious."
Also, in December 2008, IARC published a major world cancer report, noting that they had high expectations that epidemiological studies would discover the dietary habits associated with increased or decreased risk of cancer. Those expectations were not realized, IARC wrote in the report: Results from large prospective cohort studies and randomized trials provided evidence that apart from some specific cancers (e.g., stomach cancer), diet accounted for at best a minority of cancers. In particular, intakes of fat, fruit and vegetables and of meat were either not associated or only slightly associated with colorectal, breast and prostate cancer occurrence.
Clearly there is a great deal of inconsistency in this type of research.
¡°Consumers should set this latest study of the week aside or they may experience another case of nutrition whiplash, Hodges said.
To view other meat industry updates, link to the American Meat Institute.