The importance of fibre in the diet is being recognized more and more. The concept that fibre could play a preventive role in colon cancer was first proposed in 1971 when Burkitt put forth the proposal that fibre could prevent colon cancer by regulating the speed and bulk of the food that passes through the intestines.16 Since that time many studies have shown this hypothesis to be true.17 Whole grain consumption in particular, was found to be inversely correlated to the prevalence of colon cancer.18 Vegetable fibre was also shown to offer protection, and the NCI (National Cancer Institute of the US) has therefore recommended that a variety of foods such as whole grains, vegetables and fruits be eaten rather than fibre supplements, and that dietary fibre levels should at least be doubled over current consumption levels of 10-15g fibre/day.19 Fibre consumption is so low in industrialized countries, because of the excessive consumption of refined foods. Modern grain mills, for example, separate the natural fibres and wheatgerm
from the wheat, thus stripping the wheat of its natural fibre. The bran of wheat is rich in NSP (non starch polysaccharides or fibre) which provides bulk and aids intestinal motility. Furthermore, these outer layers of wheat include the aleurone layers which contain the B-complex vitamins, phosphorus, iron, and proteins in balanced proportions. The wheatgerm is rich in thiamin (vitamin B1) which is essential for carbohydrate metabolism and the natural antioxidant vitamin E. Vitamin E comes prepacked with the polyunsaturated oils in the wheat-germ and thus offers a natural protection against the formation of free radicals when these essential oils are ingested. Whole grains or unrefined grain products such as stone-ground flour, are thus vastly superior to refined products in terms of their overall composition.
The addition of unground wheat berries or broken pieces of grain to the flour is also a poor way of adding fibre to grain products. These hard pieces pass through the intestines largely undigested, add little bulk and can even damage the delicate epithelia on their way. They do not aid in water retention in the stools and do not provide a large enough surface area for the elimination of wastes. Flour used for bread-making should be thoroughly ground and if whole grains are used for the preparation of porridges, then they must be well soaked or/and thoroughly cooked, as raw grains contain enzyme suppressants which interfere with the digestive process. Cooking or sprouting destroys these suppressants and thus allows for maximal utilization of the nutrients in the grains.
As fibre content in the diet increases, bowel transit time decreases and faeces weight and the number of defecations increase.20,21 Furthermore, the consistency of the stool is far softer on a natural high-fibre diet than on a low-fibre diet thus eliminating constipation and its secondary effects such as colitis, appendicitis, diverticulosis, and hiatus hernia. Oats and bean products contain large quantities of water-soluble fibre and are particularly efficient in reducing blood cholesterol levels, particularly LDL-cholesterol, which is the variety which tends to clog blood vessels. 22,23,24,25,26 It was found that the inclusion of oat-bran and beans in the diet decreased LDL-cholesterol concentrations by 23% and 24% respectively in a study done on 20 hypercholesterolaemic adult males.22 Added bran is not nearly as efficient in eliminating cholesterol as is the fibre in whole cereals,27 thus emphasizing the importance of the consumption of whole, unrefined foods as means of controlling cholesterol levels. Some studies suggest that oat bran acts as a placebo,28,29 but other studies have shown that this conclusion is probably unfounded.30 By binding cholesterol and bile acids, fibre not only reduces cholesterol levels but also protects against colon cancer, as secondary bile acids, which are formed by bacterial conversion of bile acids, are carcinogenic.31 The relationship between the incidence of colon cancer and fibre intake is presented in Figure 2.6.
Figure 2.6 Average regional NSP intake in relation to age standardized colon cancer death rates 1969-1973 in Great Britain. (Adapted from reference 32)
Wheat-bran was also found to lower the concentrations of oestrogens in women, particularly serum oestrogen and oestradiol.33 The presence of free and albumen-bound oestradiol has been associated with an increased risk of breast cancer,34 and the bran can thus offer protection against this form of cancer. Precisely how fibre affords protection against this form of cancer is uncertain. When dealing with fibre, it is important to note that there are two categories of fibre, and these two differ in their function.