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Media Drop Ball on Fiber-Colon Cancer Connection
A little closer reading of the results indicates a somewhat different headline, says Jeff Leach
Jeff Leach (zinjboss)     Email Article  Print Article 
Published 2006-01-17 11:04 (KST)   
Newspapers and health Web sites throughout the world have plugged the story much the same: "Dietary fiber not protective against colon cancer" and the predictable follow-on "no need to eat fiber anymore." The CNN Web site(1) pretty much sums up the common theme among news reports with their own pronouncement, "Harvard researchers burst a lot of bubbles by reporting that dietary fiber doesn't reduce the risk of colorectal cancer."

The problem is -- they all got it wrong.

In their rush to get out the "no need to rough it with roughage" story, following the publication by Harvard researchers in the Journal of the American Medical Association (2) of a report on dietary fiber intake and the risk of colorectal cancer, reporters forgot to read the report -- at least carefully.

In their study the Harvard researchers pooled the data from 13 separate studies that tracked 725,628 men and women over a six to 20 year period to assess the role of dietary fiber intake in the development of colon cancer. One of the conclusions reached in the study, and the one parroted by news reporters around the world read, "High dietary fiber intake was not associated with a reduced risk of colorectal cancer."

A little closer reading of the results and a review of the accompanying editorial (3) published in the same issue, however, would indicate that a somewhat different headline may be in order for any reporter willing to take the time.

According to the U.S. Food Pyramid, a daily intake of 20 to 38 grams a day of fiber is recommended, depending on age, gender, and activity level. For most adults this means something near 30 grams a day.

In the Harvard study the difference in fiber intake among the pooled data from the lowest to highest was 14 to 28 grams for men and 13 to 24 grams for women. This means the average participant was eating far less than the recommended daily amount of fiber.

According to an editorial published in the same issue, John Baron, Professor of Medicine and of Community & Family Medicine at Dartmouth Medical School, made the following observation after reviewing the complicated analysis and statistics presented in the Harvard report: "Park [lead Harvard researcher] found evidence of an increased risk of colorectal cancer among individuals with very low intake of total dietary fiber ... After adjusting for measurement error, the relative risk for intakes of less than 10 g per day versus 10 or more g per day increased from 1.22 to 2.16."

Translation: people with the lowest fiber intake were at nearly twice the risk for colon cancer than those with the higher fiber intake. This critical information was missing in the numerous reports appearing in newspapers and websites read by millions of consumers eager to improve their overall health and well-being.

This same editorial went on to say "the European Prospective Investigation into Cancer and Nutrition (EPIC) investigators found a more than 40 percent reduction in the risk of colorectal cancer for individuals in the highest quintile of dietary fiber intake vs the lowest ... The findings by Park and the results of the EPIC analysis provide at least some indications that dietary fiber of some sort is related in some way to colon or rectal cancer risk."

The EPIC study (4) referenced in the editorial was a prospective study of over half a million participants between the ages of 27 and 70 from 10 European countries that found that fiber played a protective role in the risk of colorectal cancer. The Harvard analysis did not consider the EPIC study in its analysis.

As the Harvard study suggests, the black and white role of fiber in the risk of developing colon cancer is not as clear-cut as most would like. The data and subsequent sophisticated analysis are further complicated by the fact the in all of the studies pooled in the Harvard analysis, daily intake of fiber was generally low across the board and even lower from an evolutionary perspective, revealing that our ancestors ate much greater amounts of fiber (75 to 150 grams a day) and that all of the pooled study participants were on Western diets.

Western diets, which are notoriously high in saturated fat, cholesterol, and red meat, are considered risk factors in the development of colon cancer.

The role of the "low across the board" fiber intake noted in the Harvard analysis and the complicating factors of Western dietary habits is well illustrated in a global analysis (5) of the incidence of colorectal cancer. For example in the 1960s men living on a high fiber (non-Western) diet with fiber intakes closer to our evolutionary intake of 100 grams or more a day had an incidence of colorectal cancer of 3.5 per 100,000 in Uganda and 5.3 per 100,000 in Mozambique. Compare this to low-fiber, Western diets in Scotland and the United States that produced an incidence of colorectal cancer of 51.5 and 51.8 per 100,000, respectively.

This means a nearly ten-fold increase in the incidence of colorectal cancer based on a low versus high intake of fiber and whether or not a Western-style diet is consumed.

In future studies it would be useful for researchers to consider an evolutionary perspective on fiber intake while using more refined statistical techniques with populations who are clearly eating extremely low amounts of fiber in the first place.

As long as researchers, reporters, and the general public consider current U.S. Food Pyramid guidelines on fiber intake as adequate or on the high side and continue to derive and compare results only to populations eating highly-processed, high-fat, added-sugar, and high red meat diets, meaningful conclusions on the important role of dietary fiber in human health may not be forthcoming.
(1) CNN blurb: "Fiber Flops"

(2) JAMA report (JAMA. 2005; 294:2849-2857)

(3) The accompanying editorial (JAMA. 2005; 294:2904-2906)

(4) EPIC study (The Lancet, Vol.361, No. 9368, pgs 1496-1501)

(5) Lawlor DA, Ness AR. "Commentary: the rough world of nutritional epidemiology: does dietary fibre prevent large bowel cancer?" (PDF) Int J Epidemiol. 2003. 32(2):239-43.
©2006 OhmyNews
Other articles by reporter Jeff Leach

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