Complementing the action of insoluble fibres, some soluble fibres also add to faecal bulk and increase its water content. But soluble fibre’s potential for reducing blood cholesterol levels has recently been considered of greater significance. Studies have shown that diets rich in soluble fibres such as oat bran may help reduce total cholesterol and low density lipoprotein (LDL) cholesterol in people with both high and normal blood cholesterol levels. Margo Denke, M.D., a nutrition research scientist at the University of Texas South-western Medical Centre, estimates that a diet low in fat and high in soluble fibre may reduce an individual’s blood cholesterol by 3 percent to 6 percent.
Soluble fibres appear to reduce blood cholesterol in two ways. Firstly, they prevent the reabsorption of vital bile acids from the small intestine. To replace the lost bile acids, cholesterol is drawn from the body, hence reducing its cholesterol supply. Second, the fermentation of soluble fibres in the intestine produces short-chain fatty acids which block the synthesis of cholesterol.
As it is known high cholesterol levels in the blood is a major player in the development of coronary heart disease. But just having extra cholesterol floating around your bloodstream is not enough to cause coronary plaques to form. The mechanism for plague formation is a very complex one involving the interplay between the cholesterol molecule, the body’s clotting mechanisms (which include platelets) and blood sugar level. Cholesterol might be thought of as the bricks with platelets and other clotting factors as the cement and the wall of the artery as the surface to be covered. If the surface of the arteries is very smooth, then it is difficult for the cholesterol to attach to it, but as the arterial wall becomes less smooth, which occurs naturally with age it can activate the clotting factors more easily. These clotting factors allow the cholesterol to stick to the wall of the artery. The rougher the wall gets, the easier it is for the cholesterol to attach itself. For reasons that are still unclear, elevated blood sugar levels seem to enhance the whole plague formation process. It has been known for years that diabetics have much higher rate of coronary heart disease at a younger age. A blood sugar less than 115 was considered normal and levels greater than 140 to be abnormal with 115-140 an intermediate range. We always assumed that if the fasting blood sugar was less than 140 and certainly less than 115, the body didn’t activate the same mechanism we see in diabetics that lead to premature heart disease. But recently the Framingham study found that blood sugars over 90 increase the likelihood of plague formation. Again fibre is the substance that helps prevent this ( the mechanism linking stress to coronary heart disease is that it increases your cholesterol level, makes your platelets more sticky, and therefore more likely to clot. It also increases your blood sugar level – all the factors that lead to coronary heart disease.)
In some parts of the world, food science is giving “nature’s most complete food” a nutritional boost. In Japan, for example, the country’s largest dairy, Show Brand, has introduced a milk fortified with dietary fibre and Vitamin E. Packaged in the country’s popular 300ml-sized carton, the milk called “Seni-i-Jijutsu” (which translates to – “plenty of dietary fibre”), contains 5.3 grams of fibre in the form of Litesse, a bulking agent developed by Cultor Food Science. That’s about the amount of fibre found in six sticks of celery. The fibre fortification is a revolutionary idea since due to the over- consumption of processed foods in their country, the Japanese do not eat as much dietary fibre as they should. The new milk also supplies 8 mg of Vitamin E which is enough to provide the recommended daily requirement for both men and women.
Most food composition data bases today reflect the crude fibre content of food, which is determined by subjecting food to a chemical treatment that destroys large amounts of its insoluble fibres and almost all of its soluble fibres. The resulting value seriously underestimates the true dietary fibre content of food, which has been judged to be three to five times higher. This created difficulties when attempting to evaluate fibre intake.
Methods that provide a more accurate reading are now in limited use in the United States. The neutral detergent fibre method is primarily useful in estimating insoluble fibre content. The total dietary fibre (TDF) method is the only process that estimates total fibre content. The Association of Official Analytical Chemists, which establishes all accepted U.S. methods for determining nutrients in foods, advocates use of the TDF method. Modification of the TDF method also allows determination of soluble and insoluble fractions, but provisional data bases using figures derived from this method currently do not reflect the type of fibre in a food. According to the U.S. Department of Agriculture (USDA) Human Nutrition Information Service, an update of the information is expected in the near future. Currently, there is no universally accepted method for determination of dietary fibre. For some years the UK Ministry of Agriculture, Fisheries and Food (MAFF) has adopted the definition, for the purposes of label declaration, that dietary fibre is non-starch polysaccharides as determined by the Englyst method; but in Guidelines issued in March 1994, MAFF indicated that analysts may use any other methods which give similar results. The Englyst method excludes resistant starch. Most EU countries and the USA use the AOAC Prosky method. This method includes resistant starch and the value for dietary fibre obtained is therefore invariably higher than that by the Englyst method. It should be noted, however, that no recognised analytical method fully corresponds to biological performance.
Indeed, dietary guidelines issued by the USDA, the U.S. Department of Health and Human Services, and the Surgeon General’s office emphasize an increased intake of fibre-rich foods in general. Fibre supplements are not recommended as a way to meet dietary guidelines.
The Diet and Health report of the National Academy of Sciences has gone one step further by specifying recommended amounts of foods high in fibre. It advises a daily intake of five or more servings of fruits and vegetables and six or more servings of whole grain breads and cereals and legumes. Health professionals caution against making an immediate leap from a low-fibre intake to recommended levels. As noted earlier increasing fibre consumption too rapidly can result in flatulence, cramping and intestinal distension. Undesirable side effects may be avoided through the gradual addition of fibre to the diet along with an adequate fluid intake. Although concerns that fibre may interfere with the absorption of trace minerals have been voiced, studies show people consuming well-balanced and varied diets high in fibre are unlikely to experience mineral deficiencies.
While fibre does seem significant to human health, scientists stress its connection with other factors must not be ignored. The effects of heredity, the quality of the overall diet and habits such as smoking and exercise can easily outweigh any single dietary modification. The best guarantee is an integrated effort that includes a high-fibre diet as part of a healthy lifestyle. Fibre’s significance in maintaining a healthy body and regulating sugar levels within it, together with the prevention of coronary heart disease and cancer, is too important to be overlooked. Research in this field must continue in order to enhance our knowledge of the advantages and disadvantages of dietary fibre since it is a very crucial part of the human diet.