Fibre supplements (also spelled fiber supplements) are considered to be a form of a subgroup of functional dietary fibre, and in the United States are defined by the Institute of Medicine (IOM). According to the IOM, functional fibre "consists of isolated, non-digestible carbohydrates that have beneficial physiological effects in humans".
Fibre supplements are widely available, and can be found in forms such as powders, tablets, and capsules. Consumption of fibre supplements may be for: improving dietary intake, lowering blood cholesterol, alleviating irritable bowel syndrome, reducing the risk of colon cancer, and increasing feelings of satiety.
Excessive fibre intake can lead to fluid imbalance, dehydration, mineral deficiencies, nutrient and drug interactions, and other medical problems.
Rationale for fibre supplement use
The American Dietetic Association recommends that the average adult consume 25 to 38 grams of dietary fibre per day. However, research has shown that the average American only consumes 14 to 15 grams per day. To reach the recommended amount of fibre, consumption of dietary fibre from foods (e.g. plants, vegetables, legumes, and grains) instead of supplements is preferred because they contain additional beneficial nutrients and non-nutritive components (e.g. antioxidants and phytoestrogens). Nevertheless, a fibre supplement may be needed to prevent constipation when food intake is low, which is the case among inactive elderly. A cereal bran such as psyllium seed husk, or a synthetic fiber such as methylcellulose is often used in this case.
Health claims
Blood cholesterol reduction
Foods that are high in viscous fibres have been found to lower blood cholesterol by binding with bile acids. In order to compensate for this, cholesterol from the liver may be used to make more bile acids. The products of bacterial fermentation in the colon may also decrease the rate of cholesterol synthesis in the liver.
However, research has produced mixed results with respect to whether fibre supplements are as effective as dietary fibre in reducing blood cholesterol. Two recent studies show nearly opposing results, using fibre-supplemented apple juice containing both the soluble pectin from apples and gum arabic. In the first study, the supplement-enriched juice had no discernible effect on the blood cholesterol levels of 110 hypercholesterolaemic men and women. In the second study, the total and LDL-cholesterol levels of mildly hypercholesterolaemic men were lowered.
In another study, a dietary supplement consisting of both soluble fibre (guar gum, pectin) and insoluble fibre (soy fibre, pea fibre, corn bran) was found to reduce LDL-cholesterol for individuals that have mild to moderate hypercholesterolaemia without reducing HDL-cholesterol or increasing triglycerides.
Supplements containing extracted insoluble fibre may have an effect on blood lipids that most resembles the effects of dietary fibre. In a more recent randomized, double blind clinical study of 58 hypercholesterolaemic volunteers, an extruded carob pulp preparation added to daily diet reduced total and LDL-cholesterol and improved the ratio of HDL:LDL cholesterol in all participants, and also showed a marked reduction in serum cholesterol in the women of the study.
Gastrointestinal health
Colorectal cancer
The protective properties of dietary fibre against colorectal cancer are undisputed. However, not all fibre supplements seem to provide the same defensive effect. A study of 1429 men and women over six months showed that a high-fibre cereal (wheat bran) supplement had no protective effect on recurring colorectal adenomas. In addition, no significant improvement in the proportion or features of existing colorectal adenomas was observed.
Diverticular disease
Diverticulitis is mainly attributed to the low fibre intake typical of the Western diet for which gradual increase dietary fibre over several weeks is common clinical solution. Fibre supplements are again much less effective. One study of 58 men and women with uncomplicated diverticulitis in a double-blind controlled trial concluded that common doses of wheat bran and a psyllium-derived supplement provided relief of constipation only, with no other observable effects.