Does Fibre Protect Us From Colon Cancer?

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While many of us may be committed to the idea of eating a healthy diet, it can often be difficult knowing precisely what that is. There’s a tremendous amount of information out there on diet and nutrition but, to be frank, much of it is conflicting and contradictory. More confusion was added to the area recently on the publication of two studies which suggested that eating a high fibre diet may not protect us from colon cancer. For almost 30 years, the value of eating ‘high-fibre’ foods has remained a central theme of what is believed to constitute a ‘healthy’ diet. Now, some doctors and scientists are suggesting that we might have been misled, and that fibre may not have the health-giving properties that have traditionally been ascribed to it. So, is there real benefit to be had from eating fibre, or has the time come to temper our enthusiasm for this dietary element.

The idea that eating a diet rich in fibre might help promote health and reduce the risk of certain conditions was popularised by the British physician Denis Burkitt in the 1970s. Dr Burkitt was interested in why it was that individuals living in rural Africa had a reduced risk of certain conditions including heart disease and cancer of the colon compared to Westerners. After many years of research he concluded that the major lifestyle difference between the two populations was the amount of fibre each consumed in its diet. Dr Burkitt summarised his research by suggesting that there was essentially two sorts of country: those in which the population ate a lot of fibre, passed big bowel motions and had small hospitals, and those in which individuals had relatively little fibre in the diet, passed small stools and had big hospitals.

Dr Burkitt had a special interest in cancer of the colon. Largely as a result of his work, scientists came up with a theory to explain why more fibre in the diet might protect against this condition. The idea was put forward that faeces contains certain toxins which may induce cancer in the bowel wall. It was suggested that eating plenty of fibre ‘diluted’ these toxins, thereby reducing their tendency to trigger cancer. Also, by speeding the rate at which faeces passes along the gut, a fibre rich diet may confer additional protection by reducing the time toxins had to exert their cancer-inducing effect.

These ideas have been enshrined in medical teaching for the best part of three decades. Then, last year, two studies were published which challenged this conventional wisdom. Both studies studied individuals who had previously suffered from polyps in the colon. Polyps are actually non-cancerous growths, but 5 ” 10 p.c. of them are believed to turn cancerous in time. In one study known as the Polyp Prevention Trial, subjects who were switched to a low-fat, high fibre diet did not experience protection from polyps over a four-year period. In another trial, known as the Wheat Bran Fiber Study, addition of wheat bran to the diet for three or more years was not found to reduce the risk of further polyps. The results of these studies was seen by many to be surprising and disappointing.

However, before we turn our backs on fibre, I think it is important to take the results of these two studies in context. First of all, I am not convinced that we can necessarily take this recent research at face value. My major qualm with the studies is that they only studied the effect of dietary change over a few years. Although the result at first glance do mot look good for fibre, they essentially have told us nothing about the effect of fibre consumption on colon cancer (remember, the studies looked only at non-cancerous polyps). In order to really know what is going on, much longer-term studies would need to be performed which tracked colon cancer rates and deaths due to this disease.

Another point which I think is relevant is that in order to assess the value of any food element in health, it is not appropriate to look at one part of the body (i.e. the colon) and one condition (i.e. cancer). Even if it turns out that fibre does not reduce the risk of colon cancer, we really do need to take an overview of all the available research. Increased fibre consumption has been associated with a reduced risk of heart disease (the number one killer in the Western world), high blood pressure and a condition known as diverticular disease in which little ‘pockets’ form in the lining of the large bowel which may become infected with serious consequences in some cases.

Sometimes it can be very difficult to discern what it is about a particular type of food that gives it beneficial properties in the body. Individual foodstuffs are composed of possibly hundreds of substances which might have disease-protective effects. Fruits and vegetables, for instance, contain a range of potentially beneficial vitamins, minerals and plant substances known as phytochemicals. Even if fibre itself is found not to be particularly beneficial, there is little doubt that high-fibre foods can be protective for a range of conditions. For example, in a study which looked at the results from 206 human and 22 animal studies, an increased consumption of fruits and vegetables was found to reduce the risk of several forms of cancer including those of the stomach, oesophagus (gullet), lung, pancreas and colon. Fruit and vegetable consumption has also been linked to a reduce risk of conditions such as heart disease, stroke and osteoporosis. Another benefit of switching to a high fibre diet is that it generally leads to a reduction in intake of less healthy and potentially harmful foods such as those rich in fat.

Apart from fruits and vegetables, the other main source of fibre in the diet are the grains, especially wheat. I do have some major reservations about using wheat bran-rich products as a source of fibre in the diet. First of all wheat generally does not contain the quantity or range of disease protective nutrients found in fruits and vegetables. Also, in practice, wheat turns out to be one of the most common causes of food sensitivity (where reactions to food can give rise to an array of different health problems). Also, wheat bran has been aggressively marketed through the promotion of breakfast cereals which almost always contain significant quantities of potentially harmful sugar and salt.

The most recent research on fibre has yet to show whether or not it really does reduce the risk of colon cancer. Yet, while we are waiting for all the facts to come in, bearing in mind the body of evidence, there still appears to be plenty of good research to support the idea of including plenty of high fibre diet. In balance, it may be that increasing fibre consumption is not best achieved through the consumption of foods rich in wheat bran, but more through the increased intake of fruits, vegetables, beans and pulses.

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