VANCOUVER, B.C. — Eating healthy is supposed to include lots of fruits and vegetables containing coarse fiber. It's been pointed out that bowel cancer and heart attacks are unheard of in primitive populations which eat a fiber-rich diet of roots, seeds, whole grain and uncooked vegetables. We therefore benefit when we avoid foods made with white processed flour in favour of bran, whole wheat bread, oats, turnips and salads.
This belief burst upon the world somewhere around 1970, conceived in the fertile mind of Denis Burkitt, a strongly religious surgeon working in Africa. He noticed that Africans passed large stools and had relatively few cancers of the bowel. "America is a constipated nation. If you have small stools you have to have large hospitals" is one of his quotes.
Important geographic differences in the incidence of colon cancer were also found, which suggests that environmental factors like diet might be involved. People who move from high-risk to low-risk areas gradually assume the risk profile of their new home, reinforcing this concept. This kind of information was enough to start, with the assistance of the good doctor, another act in the morality play of healthy eating.
Dr. Burkitt almost single-handedly prompted the flowering of belief among civilized Western people that if we cut back on the soft manufactured food and did more rooting around for parsnips and other harsh fare we would change our pattern of disease to be more like that of people living in Africa. Minus, of course, the malaria, yellow fever, epidemic HIV, rabies, snake and other wild animal-related deaths and parasite infestations.
To see whether there was any scientific support for eating fiber-rich food (which I don't like much), I reviewed 22 studies of fiber and health. The 2004 review by the Cochran Collaboration1 of high-quality studies found no fewer precancerous polyps in high-fiber eaters. Another review of prospective observational trials2 found no decrease in colon cancer risk with a high fiber diet. There was no improved risk of prostate cancer with fiber, and for cancer of the uterus lining the difference shown in observational studies was not borne out in the one better-quality prospective study examined. For heart disease, the only difference fiber made was to reduce blood pressure by an amount so tiny doctors' instruments couldn't measure it3.
One fiber analysis on cardiovascular disease that I reviewed4 found that a high-fiber diet couldcut the risk of heart disease by just over two per 10,000. This meant that 96 to 97 per cent of people would get no heart disease benefit from lifelong fiber consumption. The analysis methodology was good, but many of the studies weren't, so there isn't much support for a huge change in fiber consumption to prevent heart disease. A recent Cochrane study5 of higher-quality randomized trials of whole-grain cereals and heart disease contradicts this study by finding effects on surrogate endpoints only.A 2008 Cochrane review of dietary fiber and diabetes6 was negative.
It looks like fiber promoting health doesn't have much basis in credible science. But belief that fiber saves lives has resulted in the disappearance of adequately-cooked vegetables in restaurants, and our facing millions of metric tons of salt- and sugar-free baked goods packed with harsh, sawdust-like substances.
I seem to hear in Burkitt's "America is . . . constipated" language a criticism of the way we live that goes beyond the food we eat. High-fiber dietary advice sounds to me like a call to abandon a soft, convenient life and return to direct contact with the earth and the fundamental economies of a work ethic. It happens I kind of like that idea. Most of us could do with a little more simplicity and hard work. But by the same metaphoric magic through which we come to hate fat and be afraid of sugar, we are invited to commit ourselves to the roughness of fiber in food as though it will somehow scour the moral and diseased nastiness out of our insides.
Give me soft crisp traditional white flour sweet and salty pastries thanks, and vegetables done just on the border of crunchy. I can't find any scientific basis for denying myself these treats, and I don't think I would benefit much from imaginary internal cleaning out either.
REFERENCES
1.T. Asano and R. McLeod, “Dietary fiber for the prevention of colorectal adenomas and carcinomas,” Cochrane Database of Systematic Reviews, Issue 2 (2002).
2. Y. Park et al, “Dietary Fiber Intake and Risk of Colorectal Cancer: a Pooled Analysis of Prospective Cohort Studies,” Journal of the American Medical Association, 294( 22): 2849-57 (Dec 14, 2005).
3. M. Streppel et al, “Dietary Fiber and Blood Pressure: a Meta-Analysis of Randomised Placebo-Controlled Trials,” Archives of Internal Medicine, 165( 2): 150-6 (January 24, 2005).
4. M. Pereira et al, “Dietary Fiber and Risk of Coronary Heart Disease A Pooled Analysis of Cohort Studies,” Archives of Internal Medicine, 164:370-376 (2004).
5. S. Kelly et al, “Wholegrain cereals for coronary heart disease,” Cochrane Database of Systematic Reviews, Issue 2 (2007).
6. M. Priebe et al., “Whole grain foods for the prevention of Type 2 diabetes mellitus,” Cochrane Database of Systematic Reviews Issue 1 (2008).
John Sloan is a family physician whose practice is confined to home care of frail elderly people, and avoiding institutional care of these patients. He has published numerous articles and several books on healthcare. His most recent ebook is Forbidden Food: How Science Says you can Eat what you Like and Like what you Eat.
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