Fibre – the pendulum swings
The publication in the Lancet of a study concerned with the effect of dietary fibre on bowel cancer makes interesting, if depressing, reading. Claire Bonithon-Kopp and her colleagues of the European Cancer Prevention Organisation Study Group have obtained findings which appear to challenge long-held assumptions that diets rich in fibre help prevent not only heart disease but also colorectal cancer.
The study involved three randomised groups of patients with a previous history of adenomas – small polyps attached to the wall of the bowel which can be precursors of cancer. One group was given fibre supplements, another doses of calcium, also thought to reduce the incidence of bowel cancer, and the third received a placebo over a period of three years.
At the end of the trial the reoccurrence of the polyps in the 'calcium' group was 16%, compared with 20% for the placebo control group. Among those who had been given fibre supplements, however, polyps were found to have reoccurred in 29% of the group – a statistically significant higher proportion.
The authors of the study express a number of qualifications regarding these results, as we would expect in peer-reviewed journal. They point out, for example, that ". because very few patients developed large adenomas, we cannot exclude the possibility of a beneficial effect of ispaghula husk [fibre] on later stages of carcinogenesis, such as adenoma growth and malignant transformation." They also emphasise ". our findings should not prevent recommendations for high consumption of vegetables, fruits and cereals, because this approach has potentially beneficial effects on other chronic disease, especially coronary heart disease."
The study has been reported in a number of British newspapers, including the Independent and the Express in a generally accurate way. The fact that this was a study of people who already had precursors for bowel cancer in the form of polyps was not always made clear, but a sense of balance has been evident.
What this study really highlights is the near impossibility of providing definitive dietary prescriptions when the body of scientific evidence on which they are, or should be, founded is constantly shifting. High fibre is still good for the heart, but now it is possibly bad for the bowel. Dairy products, once thought to be so essential for good health that some of us still remember being force-fed full-fat milk at primary school, are now seen as potentially hazardous conveyors of cholesterol. And red meat, another alleged villain of cancer causation, is now firmly on the school meals menu to prevent nutritional deficiencies.
It is difficult to find any single food item that has not, at one time or another, been found to be both beneficial and, at others, toxic or carcinogenic. Broccoli, perhaps, is one of the few which has survived the pendulum swings of dietary correctness.
We at SIRC are currently developing a time-line of dietary recommendations to illustrate how quickly things can change, and how quickly people forget that many of things they now avoid on their plate were once thought entirely good for them – and vice-versa. Any contributions to this work will be extremely welcome.
In the meantime, instead of being slaves to whatever dietary fad is currently fashionable, we might take a leaf out of Desmond Morris's book and start to believe that 'A little bit of what you fancy' might actually be good for you as well. Perhaps it is not always food itself which makes us ill. Perhaps it is the fear of food, and the anxieties that people currently experience about eating 'correctly', which will turn out to be the bigger villains.