Fibre is a term describing the substances in plant food which are not digested. Fibre provides almost no calories. This group of compounds consists mainly of complex carbohydrates.
Although not digested in the small intestine, some of the soluble fibre will be metabolised by our own bacteria in the large intestine. The resulting substances help acidify the colonic contents, resulting in water retention and faecal bulking. The faecal bulking and water retention by the stool enable a relatively rapid transit time for the stool. This may help protect the cells of the large intestine from the effects of ingested toxins and the harmful effects of bile acids and faecal water, potentially reducing our risk of developing colon cancer.Br J Nutr. 2003 Dec;90(6):1057-70
In addition, fibre consumption has recently been associated with a reduction in weight gain and insulin levels. Dietary fibre can also help to reduce the risk of developing heart disease and has been shown to play a role in reducing blood pressure. Dietary fibre has also been shown to play a role in reducing the level of LDL cholesterol and TGs, both risk factors for heart disease JAMA. 1999 Oct 27;282(16):1539-46.
Dietary fibre and resistant starch: a re-evaluation
Research over the past 20 years has revealed some important differences in the roles of insoluble and soluble dietary fibres. Insoluble fibres such as cellulose and lignans play an important role in maintaining faecal bulk and intestinal health. Soluble fibres, on the other hand, have a more important metabolic role. They are found in fruit, vegetables and cereals as pectins, gums, mucilages, hemicelluloses and resistant starch (RS). The metabolism of these soluble fibres is known to control blood glucose and cholesterol levels. Resistant starch is the most important member of the group, and its concentration in foods can be increased by cooking and processing. Like the other soluble dietary fibres, RS is fermented in the colon to provide long-term energy. It does not evoke an insulin response and is referred to as non-glycaemic carbohydrate. Resistant starch is a crucial dietary component for weight and blood glucose management and intestinal health.
Traditional diets rich in whole grains, vegetables and fibre have long been known to protect against obesity, diabetes Type 2, and several cancers. The major protective component in these diets, and often lacking in Western diets, is resistant starch. This is classed as the plant starch fraction that escapes digestion in the small intestine and passes into the colon. There it is slowly fermented by the resident bacteria to produce butyric acid which the main energy source for the cells of the colonic epithelium, the colonocytes. This production of butyrate protects against colon cancer, and helps to control blood glucose levels.
Dietary recommendations for resistant starch
Resistant starch consumption in the developed world is calculated at 3–7g/day. The WHO recommends a total dietary fibre (soluble + insoluble) intake of >25g/day, whereas the CSIRO in Australia recommend 20g/day of resistant starch for optimum bowel health. Some clinicians and nutritionists are now suggesting a daily intake of 25g for women and 40g for men for optimum health benefits since a high intake of resistant starch appears to have no unwanted side effects. Green bananas are a cheap and readily available source of resistant starch.
The unique dietary properties of resistant starch
· Gives some of the benefits of insoluble fibres as well as multiple benefits of soluble fibres.
· Improves the glycaemic response by increasing insulin sensitivity.
· Reduces obesity by stimulating fat oxidation.
· Reduces the inflammatory response.
· Helps to establish a healthy large bowel microflora.
· Reduces the risk of colon cancer by generating butyrate in the large bowel.
· Pure RS is gluten free and can replace flour in wheat-free and coeliac diets.
· Lowers the calorie content of foods by 50% when replacing refined flour or sugars.
· The physical properties of RS allow it to be incorporated into normal foods like bread, pastries, cakes, biscuits and drinks without causing consumer rejection.
· Reduces hunger pangs for two to three hours in the short term and 20–24 hours in the longer term.
· Helps to maintain bowel regularity by increasing microbial activity in the large intestine, to cause a mild laxative effect.
The facts listed above reveal how important resistant starch is as a crucial component of a healthy diet.
Other beneficial soluble dietary fibres.
Β-glucans, pectins, and inulin play a crucial role in supporting intestinal colonisation by beneficial bacteria which then exclude the more harmful species such as Pseudomonads, E.coli and Firmicutes. Antibiotic therapy following illness or surgery can lead to overgrowth by these organisms if an unhealthy sugar-rich diet is followed. Their presence stimulates inflammation in the gut wall and leads to ‘leaky gut syndrome’, which allows normally excluded toxins and bacteria to penetrate the intestinal barrier and enter the circulation. This results in a massive immune response and can initiate a wide range of inflammatory diseases from heart disease and cancer to dementia.
NB Growth factor for beneficial gm +ve gut bacteria eg Bifidobacteria. Fermented oatmeal with Bifidobacterial inoculum, and added inulin .