09 February 2000 --
Food fads may come and go, but the importance of a well-balanced diet never goes out of style.
One of the most important components of a healthy diet is fibre. While it may not be the most exciting part of the diet, eating foods high in fibre is essential for good health and reduced risk of several diseases.
This recommendation is as strong today as it was more than 20 years ago when fibre hit the headlines after it was noted that African tribes who took a diet high in fibre had lower risk of several diseases. Scientific studies continue to produce new evidence to support the need to increase fibre in the diet.
Dietary fibre is found only in plants. Dr Dennis Gordon, a researcher in nutrition and dietary fibre at North Dakota State University in the US, defines fibre as "food carbohydrate that is not digested or absorbed and which contributes to positive physiological functions in the body".
Soluble and insoluble fibre
If you've read up on dietary fibre, you may know that most scientists classify fibre as either "soluble" or "insoluble". This refers to whether the fibre dissolves in hot water. More importantly, it helps to explain the different actions of the two types of fibre in the body.
The largest amount of fibre in our diet is insoluble fibre. This type of fibre provides texture to fruits, vegetables and cereals. Insoluble fibre helps bind water in the intestine and increases the volume of waste materials. The end result is more frequent and softer bowel motions and less risk of constipation.
Soluble fibre is found in all fruits, some cereals (such as oats and barley) and in legumes (dried peas and beans and lentils). This type of fibre acts as a natural thickening agent in foods. For example, if you add lentils or beans to a curry, they help to thicken the curry.
When we eat soluble fibre, it traps fatty substances in the intestines thereby helping to prevent their absorption by the body. This is thought to be the reason that soluble fibre helps to lower blood cholesterol levels. Soluble fibre also has beneficial effects on blood glucose levels.
The combined actions of soluble and insoluble fibre are important in helping to maintain a healthy population of bacteria in our large intestines. Fibre in the large intestine acts as a source of energy for these bacteria to use. Fermentation of fibre in the large intestine helps promote the growth of more lactic-acid producing bacteria. A predominance of lactic acid producing bacteria helps to prevent the accumulation of toxic and pathogenic (disease-causing) bacteria.
How much fibre?
Most health organisations agree that adults should consume between 20 and 35 grams of dietary fibre a day. Yet most people in Asia fail to reach this amount. According to the national dietary survey of Singaporeans (1983), average fibre intake is just 15 grams a day. In Hong Kong, a 1995 study estimated that fibre intakes averaged less than 10 grams a day.
Yet not only is it easy to increase fibre intakes, it's also vital to good health. Dr Gordon warns, "There are many diseases or disorders frequently related to inadequate consumption of dietary fibre. These diseases include cancer of the colon, high blood cholesterol, diabetes, diverticulosis and constipation."
Fibre and health
Coronary heart disease is a leading cause of death in most Asian countries including Singapore, Malaysia, China, India, the Philippines and Indonesia. The National Heart, Lung and Blood Institute, US, has reported a direct relationship between blood cholesterol concentrations and premature coronary heart disease. Dietary fibre, particularly soluble fibre, appears to lower blood cholesterol and may help to reduce the risk of coronary heart disease.
Another disease that appears to be affected by fibre is colorectal cancer, one of the most common forms of cancer in Asian countries. Although the evidence is not yet complete, a lot of research has shown that a low fat, high fibre diet may reduce the risk of this type of cancer. Dr John Potter, Fred Hutchinson Cancer Research Centre, notes, "Since 1970, a large number of case-control studies have explored the role of dietary fibre in colorectal cancer, with relatively consistent results suggesting a reduced risk with higher consumption."
A study published in a recent issue of the New England Journal of Medicine reported that a high fibre diet did not appear to affect the number of women in the test group who developed colon cancer. However, there are many questions about the conclusions of the study. Dr Potter suggests that a number of technical issues concerning this study need to be resolved, including the translation of dietary intake collected in the test group's questionnaires, biological questions about fibre itself and questions intrinsic to epidemiological studies.
More research will undoubtedly be performed to determine what effect dietary fibre has on colon cancer risk. Nevertheless, the overall benefits of dietary fibre are widely accepted and dietary fibre remains an important part of the diet. Dr Gordon and Dr Potter both agree that while one study alone will not prove a positive effect of dietary fibre on any human disease, no one study deserves to be the final word in dismissing the importance of dietary fibre for any disease.
There is no doubt that dietary fibre is beneficial to health, and more research will continue to identify the areas in which dietary fibre contributes to a healthy lifestyle.
- The Food and Drug Administration (FDA) of the United States of America, allows health claims relating to dietary fibre on food labels. Several health claims have been authorised referring to the effects of a high fibre, low fat diet in helping to lower the risk of coronary heart disease and cancer. The FDA has recently approved health claims relating to wholegrain foods and prevention of heart disease and cancers.
- In China, health claims about fibre on food packaging and in advertising are allowed provided the claimed effect has been scientifically proven. The studies to prove the efficacy of the product must be conducted in China.
- The situation is similar in Japan where foods making any sort of health claim must be classified as "Foods for Specific Health Use" and be subjected to rigorous testing of the physiological effects of the product.
- The Philippines follows a similar system to the U.S. in allowing health claims for certain food ingredients including dietary fibre.
- In other parts of Asia, the whole area of health claims on food products, including those relating to dietary fibre, is under discussion.
Reprinted with permission from the Asian Food Information Centre (AFIC). AFIC is a non-profit organisation with the aim of communicating science-based information on a broad range of nutrition and food safety issues. Based in Singapore, AFIC covers the entire Asian region except for Japan and Korea. AFIC can be reached at Tel: +65 832 7637 and Fax: +65 464 9260.
Date reviewed: 09 February 2000