CHICAGO — The risk of colon cancer recurrence is strongly associated with foods that make up the Western diet, including refined grains, red meat, processed meat and sweets/desserts, according to a study published in the Journal of the American Medical Association.
The study, "Association of Dietary Patterns with Cancer Recurrence and Survival in Patients with Stage 3 Colon Cancer," found that patients with the highest (top quintile) intake of Western diet foods "experienced a tripling in risk of recurrence or death" compared with the lowest intake.
The analysis, apparently a technically accurate description based on the statistical measure "adjusted hazard ratio," was reported in the mainstream press as concluding that three times as many subjects at the top quintile suffered recurrences than at the lowest quintile. An exploration of the data by Food Business News revealed that rather than 3:1 between the extreme quintiles, the recurrence ratio actually was 1.4:1.
The study was published by a team led by Jeffrey A. Meyerhardt of the Department of Medical Oncology, Dana-Farber Cancer Institute, Boston.
The authors noted a considerable body of research already had established a link between diet and the development of colon cancer.
"However, the influence of diet and other lifestyle factors on the outcome of patients with established colon cancer is largely unknown," they said.
The recurrence study was patterned on the earlier studies of the connection between developing colon cancer and eating a Western diet or eating a "prudent" diet. Earlier studies found a significant increased risk of developing colon cancer among people with a higher intake of a Western diet, characterized by higher intakes of red meats, processed meats, sweets/desserts, french fries and refined grains. By contrast, the earlier studies found the prudent diet, characterized by higher intakes of fruits, vegetables, legumes, fish, poultry and whole grains, was not significantly associated with a reduced risk of developing colon cancer.
The 1,009 patients in the study were enrolled in a chemotherapy study at the National Cancer Institute between April 1999 and May 2001. Dietary and lifestyle questionnaires were given to participants four months after their surgery and then 10 months later. The food frequency questionnaires were developed by a team led by Walter Willett of the Harvard School of Public Health and asked about intake of 131 food items and vitamin and mineral supplements. The survey asked about exact cereal eaten for breakfast or vegetable oil used for frying or baking.
The median follow-up from when the first questionnaire was completed was 5.3 years. Of the 1,009 patients, 324 had experienced recurrences and 223 had died. Another 28 died without documented recurrence. The patients in the study had stage 3 cancer, meaning the cancer had reached lymph nodes but had not metastasized more broadly through the body.
Patients with the highest intakes of Western diet foods "had a significant increase in the risk of cancer recurrence or mortality, and this relationship remained largely unchanged after adjusting for other predictors of cancer recurrence," the study said.
Pitted against patients with the lowest Western dietary pattern quintile, those in the highest quintile "experienced an adjusted hazard ratio for disease-free survival of 3.25." The adjusted hazard ratio for those in the second highest quintile was 1.64.
Queried about the figures, Dr. Meyerhardt told Food Business News the "tripling of risk of recurrence" cited in the paper does not mean that 3.25 times as many subjects in the top quintile experienced a recurrence as those in the bottom quintile. While describing the 3.25 figure as an accurate statistical analysis of adjusted relative risk, he said subjects in the highest quintile of those eating a Western diet had a 40% chance of suffering from a recurrence or death within five years, versus a 29% chance for those in the lowest quintile. Overall, 32% of subjects suffered from a recurrence.
Regardless of the statistical validity of the terminology in the paper, the news media widely reported the data in a way suggesting that three times as many subjects in the highest quintile suffered recurrences as those in the lowest quintile.
For example, the Globe and Mail in Toronto stated, "Among those who adhered to a Western eating pattern, patients with the highest intakes of these types of foods were three times more likely to have their cancer return or to die than those who ate less of those foods."
Similarly, The New York Times wrote, "Compared with the one-fifth whose dietary patterns least resembled the high-fat diet, the one-fifth whose patterns most resembled it were 3.25 times as likely to have a recurrence of cancer or die."
Turning to the subjects measured by intake of the "prudent" diet, the researchers failed to find a significant association with patient outcome. In effect, the researchers found that eating more "unhealthy foods" was associated with a higher risk of recurrence but that eating more "healthy foods" was not associated with reducing the risk of recurrence.
"When we added the prudent diet into the multivariate model for the Western diet, we continued to observe a significantly worse outcome with increasing intake of Western dietary pattern," the researchers said. "Furthermore, the prudent dietary pattern did not modify the effect of the Western dietary pattern."
Importantly, the researchers said further studies are under way to "better delineate specific nutrients or food groupings that may have the strongest associations."
While the researchers did not publish how many servings of Western diet foods were consumed by subjects in each quintile, Dr. Meyerhardt provided the data to Food Business News (see table on Page 20). Even though subjects in the second quintile had a slightly lower relative risk of experiencing a recurrence, Dr. Meyerhardt suggests colon cancer patients would be better served by targeting intake levels of subjects in the first quintile.
He said a possible recommendation would be to limit red meat intake to two servings per week; processed meat, one serving per week; refined grains, one per day; sugar desserts, three per week.
Asked whether the second quintile, which generated the same recurrence risk as the first quintile but with a less restrictive diet might be a better source for the recommendation, Dr. Meyerhardt stuck with his preference toward the first quintile.
"While I agree that quintile 1 and 2 did not have as much of a difference in terms of disease-free survival in the manuscript, the trend test provided is across the spectrum of the entire 1,000 patients, and thus there are likely some patients in the higher end of quintile 2 who have some relatively increased risk," he said. "Further, the comparison of quintiles uses quintile 1 as a baseline."
This article can also be found in the digital edition of Food Business News, September 18, 2007, starting on Page 20. Click