Literature continues to accumulate as to the health benefits of dietary fibre. This research is often complex and difficult to interpret, and part of this is due to the large amount of different compounds that are defined as dietary fibre. Generally any polysaccharide that is not digested by enzymes secreted by human cells during the course of digestion in a dietary fibre. However, this does not mean that fibre is not digested, as fermentation of dietary fibres does occur in the colon through the action of microorganisms. Therefore, fibre can supply energy to the consumer indirectly through this fermentation process, which results in the production of short chain fatty acids, which are subsequently absorbed. Fibre confers a number of health effects to humans, most notably the ability to improve postprandial glycaemia. This may explain the weight loss effects of dietary fibre, as exaggerated elevations in blood glucose following eating may be a cause of insulin resistance, metabolic syndrome, weight gain and type 2 diabetes.
Fibre is a diverse group of polysaccharides which can confer a variety of effects depending on the chemical structure. Plant foods usually contain specific types of fibre that relate to the original plant foods. For example fruit contains a soluble fibre called pectin, which is found only in fruit. Oats contain a specific fibre called beta-glucan. Cellulose is an insoluble fibre more widespread and can be found to some extent in most fruits, vegetables and cereals. Because different fibre types can have different health effects, it is recommended that a wide variety of plant foods are consumed in order to confer the greatest range of protective fibres. This is the basis for including variety in the diet through balancing the foods consumed to that no one food is favoured over another. As well as fibre, this strategy will also provide a wide variety of other health promoting phytonutrients, particularly antioxidant nutrients.
Dietary fibre can have different health effects in humans because of the large variety of chemical structures it possesses. A number of studies have looked at these different effects and many have reported specific association with disease for particular types of fibre. For example one study showed that in women, total fibre intake was positively associated with adiponectin, a biomarker for leanness. Total fibre intake was also inversely associated with C-reactive protein, a biomarker for systemic inflammation. However, it was fruit fibre (pectin) that was associated with a reduction in the amount of glycated haemoglobin (HbA1c) in the blood of the subjects. A high consumption of starch, relative to the amount of fibre, was associated with lower levels of adiponectin and a higher amount of glycated haemoglobin in the plasma. A high consumption of starch, relative to the amount of cereal fibre, was associated with lower levels of adiponectin. These results therefore support the contention that a high fibre intake reduces the risk of disease.
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