The nutritional literature is increasingly proving a diverse role for fibre in human physiology. Fibre is the carbohydrate component of plant foods that are indigestible to human enzymes. It is falsely assumed by many therefore that fibre contributes nothing to the energy needs of the individual. In fact, dietary fibre is digested by gut bacteria and the digestion of fibre occurs in both the small and large intestine of humans. The products of fibre digestion are short chain fatty acids such as acetate, propionate and butyrate, and these are absorbed to the circulation where they contribute significantly to energy requirements. These short chain fatty acids favourably alter normal metabolic regulation, and this may explain the ability of dietary fibre to cause weight loss, modulate plasma glucose levels and lower elevated plasma cholesterol concentrations. Some fibres such as pectin may also favourably modify the structure of intestinal villi and can improve the absorption of vitamins such as vitamin B12.
Therefore fibre does not remain completely undigested in humans. The digestion of fibre has been extensively researched in the nutritional literature. For example, in one study1 researchers measured the digestion of pectin fibre from a number of foods including cornflakes, bread, tomatoes, apples, potatoes, carrots, beans, peas and peaches. Most of the pectin was digested in the gastrointestinal tract of healthy individuals, with only 3.5 and 4.8 % of the original pectin being detected in the faeces of female and male subjects. respectively. However, when the same experiment was performed on subjects who had undergone and ileostomy operation, the amount of pectin recovered in the faeces rose to 84.7 and 53.5 % in female and male subject, respectively. Because ileostomy patients do not have a functioning colon, these results suggest that the majority of pectin digestion (55 to 85 %) occurs in the colon, with around 15 to 45 % of pectin digestion occurring in the small intestine.
Dr Robert Barrington’s Nutritional Recommendation: Fibre is likely an essential nutrient in humans as without dietary fibre a number of Western lifestyle diseases develop. In particular fibre is required to maintain normal lipid and glucose metabolism, and a deficiency of fibre results in changes to lipoprotein and glucose homeostasis. Pectin is a soluble fibre found in plants, particularly fruits, that appears to have beneficial health effects. However, the effects of fibre from different plant sources varies slightly, and so a range of dietary fibres should be included in the diet.