The Effects Of Dietary Fibre On Gut Function Biology Essay


Describe the differences between functional fiber, dietary fibre, crude fibre, total fibre, viscous and nonfermentable fibre. Give examples of the fibres that fall under these headings.

Functional fibres are the fibres that added to the food that provide health benefits (Bryd-Bredbenner et al. 2009). The examples are pectins, gums and mucilages. Dietary fibres are the structural parts of plants so they are found in all plant derived food. The bond between the monosaccharides cannot be digested by human digestive enzymes although some are digested by GI tract bacteria (Rolfes, Pinna & Whitney 2008). The examples are polysaccharides, oligosaccharides and lignins. Crude fibres are the remaining fibres after the plant matters are treated with lipid solvent, dilute acid and alkaline. They contain only the cellulose and lignin, which are the undigested fibres (Wright 2011). Total fibres refer to the functional fibres, added fibres, natural fibres and the dietary fibres. The examples are pectins, gums, mucilages, lignin, cellulose and hemicelluloses (Bryd-Bredbenner et al. 2009). Viscous fibres are the dissolves fibres which are are readily fermented by bacteria in large intestine. They dissolve and swell in water, forming gel-like in consistency. This property enables them to be thickening jams or yogurt. The examples of this fibre are pectins, gums and mucilages. They are contained inside or around the plant cells (Wardlaw & Smith 2009). Non-fermented fibres are insoluble fibres which are not easily metabolized by intestinal bacteria. Their chemical structures do not allow them to dissolve in water readily. The examples of this fibre are lignin, cellulose, some hemicelluloses from the structural parts of plants (Wardlaw & Smith 2009).

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Explain the difference between soluble fibre, insoluble fibre and resistant starch? List sources of each.

Soluble fibres are some of the dietary fibres that dissolve in water, form gels and are digested easily by bacteria in colon, which means that it is fermentable. This is usually found in oats, barley, legumes, and citrus fruits. Soluble fibres protect us from heart disease and diabetes by lowering blood glucose lever and cholesterol level (Rolfes, Pinna & Whitney 2008). Insoluble fibres are the fibres that do not dissolve in water. Thus, they do not form gels and are less readily fermented. These fibres found mostly in whole grains and vegetables. Insoluble fibres promote bowel movements and prevent constipation (Rolfes, Pinna & Whitney 2008). Resistant starches are the starches that do not digested and absorbed in small intestine. This may due to the structures and physical's properties of the starch itself as well as the efficiency for an individual to digest it. There are commonly found in legumes, potatoes and unripe bananas (Rolfes, Pinna & Whitney 2008).

Explain the effects of dietary fibre on gut function? Make links between the physiological impact of fibre and disease prevention.

Dietary fibre improves gastrointestinal health. It helps to prevent constipation by providing bulk to the faeces. Bulky faeces move through the gut faster and result in an increased stool weight, and the increased faecal bulk dilutes the effect of any genotoxic agents in the large intestine, thereby reducing the likelihood of DNA damage in the cells lining the colon. Thus, prevents colorectal cancer.

Fibre dietary reduces the risk of developing some cancers. The various components of dietary fibre are fermented by the microbial flora naturally present in the colon, to produce low levels of the gases carbon dioxide, methane and hydrogen, as well as organic acids and SCFAs. The main SCFAs produced in the human gut are butyrate, propionate and acetate. The SCFAs lower the pH of the contents of the large intestine. This is beneficial to health, because the reduced pH creates an environment that prevents the growth of harmful bacteria. A lower pH facilitates the absorption of minerals, such as calcium and magnesium. SCFAs increase the blood flow to the colon and provide fuel to the cells in the wall of intestine. Additionally, butyrate induces programmed cell death and control over the cell cycle. Therefore, this prevents the uncontrolled proliferation of abnormal cells that occurs in the early stages of colorectal cancer.

Soluble fibres form gel-like substances when they are exposed to water in the stomach and small intestine. The presence of these gels slows gastric emptying, speed up small intestinal transit, and helps control the absorption of nutrients. This can have a major impact on the rate at which glucose appears in the bloodstream and thus on the GI of a food. It can also impact on an individual's feeling of fullness and ultimately reduce the total amount of food consumed over a period.

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Insoluble components of dietary fibre trap water molecules within the branched structure. For example, wheatbran holds 2-6 g of water per gram, and fruits and vegetables hold 18-30 g per gram (BNF 1990). These fibres bind water like a sponge during transit through the gastrointestinal tract. This causes intestinal distension and help move the luminal contents through the gastrointestinal tract (Buttriss & Lunn 2007).

Explain in detail the role of dietary fibre and its effects on small intestine motility and large bowel function? List 6 suggestions for improving the dietary firbre in recipes and meals.


White pasta - use brown rice or barley (adds a nutty flavor/require longer cooking)

Pasta - wholemeal pasta/pasta with soluble fibre

Flour - use wholemeal flour, when thickening casserols use less water and add a spoonful of grain such as rice, barley or oats, wholemeal or rye flours absorb more moisture than white flour.

Vegetables - wash well but keep skin on - peel only when necessary.

Friut - wash well and peel only when necessary

Meat - halve meat content of meat dishes and add legumes/pulses. Include 3 bean mix, butter beans or other bean salad as a meat alternative with salads, s/w or pocket bread.

Fiber dietary reduces blood cholesterol and prevents cardiovascular disease. A high intake of soluble fiber inhibits the absorption of cholesterol and the reabsorption of bile acids from the small intestine (perspective). Previous study shows that specific SCFAs, propionic acid, produced in colon inhibit cholesterol synthesis in the liver (Buttriss & Lunn 2007). Dietary fibers that are soluble enhance blood glucose control. They slow glucose absorption from the small intestine and decrease insulin release from the pancreas. This contributes to better blood glucose regulation, which can be helpful in the treatment of diabetes. Adult with low fiber diets are more likely to develop diabetes than are those with high fiber diets. Dietary fibers reduce the risk of obesity. The bulky nature of high-fiber foods fills up without yielding much energy. Fibrous foods also absorb water and expand in GI tract, creating a sense of fullness.

Viscous fibres can reduce the absorption of glucose in small intestine. Small intestinal contractions create turbulences and convective currents which cause fluid circulation and mixing of luminal contents. These movements allow glucose to be brought from the centre of the lumen close to the epithelium. When it reaches proximity to the epithelium, glucose must then diffuse across the unstirred water layer (UWL). However, viscous fibres stimulate motility but decrease transit rate, because they resist propulsive contractions. As they resist propulsion, viscous fibres should similarly resist mixing contractions, hence inhibiting the effects of motility on fluid stirring. This increases thickness of the UWL, and reduce passage of glucose across the epithelium (Food and Agriculture Organization nd.).

Certain fibres have a laxative effect in bowel. Their presence in the colon affects the motility and modifies colonic transit time. The volume occupied by undegraded fibres adds to the volume of the rest of contents. These residues can trap water, thus leading to a greater bulk and create ease in the content movement. Dietary fibres reduce transit time by modulating contractile activity and water movements in the colon. First, the edges of solid particles stimulate mechanoreceptors and modify the contractile pattern of the colon in favour of a greater force of digest. Fibre could also release compound that stimulate secretion and rectosigmoid motility. Besides, undigested starch provides energy for colonic bacterial growth. Thus, some of the faecal bulking effect of dietary fibre could be due to the associated increase in starch delivery to the colon (Food and Agriculture Organization nd.).