Functional fibres refer to 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. Even though some bonds between monosaccharides can be digested by GI tract bacteria, mostly of the bonds cannot be digested by human digestive enzymes. (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. This is because 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 fibre refers to the dietary fibre that dissolves in water and slightly solidifies to form gel-like structure. Besides, it is also fermentable as it can be digested by bacteria stored in the colon. This is commonly found in oats, legumes, barley and citrus fruits. Soluble fibre helps to lower our glucose level as well as cholesterol level. Thus, this prevents us from diabetes and cardiovascular diseases (Rolfes, Pinna & Whitney 2008). Next, insoluble fibre is fibre that insoluble in water and does not solidify. Thus, it is less readily fermented by the bacteria stored in the colons. However, it helps in preventing constipation and colon cancer. This is by providing aids in bowel movement and preventing the building up of toxic substances in the colon. Insoluble fibre mostly found in whole grains and vegetables. (Rolfes, Pinna & Whitney 2008). Resistant starches are the indigestible starches that absorbed into small intestine. This may due to the structure and physical 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 enhances gastrointestinal health. It gives bulk to faeces by absorbing the water and helps to prevent constipation by intestinal distension. Insoluble components of dietary fibre store water molecules within the branched structure. These fibres bind water like a sponge during transit through the gastrointestinal tract. Large intestine contains genotoxic agents which cause DNA damage in the cells lining the colon. However, the increased faecal bulk dilutes genotoxic agents in the large intestine which eventually prevents from colorectal cancer. Besides, dietary fibre also prevents colorectal cancer by the fermentation of the fibre by microbial flora in the colon. During the fermentation, low levels of gaseous carbon dioxide, hydrogen, methane, as well as organic acids and short chain fatty acids (SCFAs) are produced. SCFAs produced in human gut are mainly acetate, butyrate and propionate. SCFAs help in lowering the pH value of the contents in large intestine so prevent the growth of harmful bacteria because bacteria are inhibited in acidic condition. Besides, low pH also facilitates the absorption of some minerals. In addition, SCFAs produced also help increase the blood flow to the colon and provide fuel to the cells in the intestine's wall. Next, butyrate helps in preventing uncontrolled production of mutant cell at the beginning stage of colorectal cancer by inducing programmed cell death (Buttriss & Lunn 2007).
Soluble fibres form gels when they are dissolves in water in the stomach and small intestine. The gels formed slower down gastric emptying and aids in regulating nutrients absorption. Therefore, less glucose can be absorbed into bloodstream. This decreases the GI of food. It can also make one's feeling of fullness and ultimately reduce the total amount of food consumed over a period (Buttriss & Lunn 2007).
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Fiber dietary reduces blood cholesterol and prevents cardiovascular disease. High intake of soluble fiber inhibits the absorption of cholesterol and the reabsorption of bile acids from the small intestine (Bryd-Bredbenner et al. 2009). Previous study shows that propionic acid produced in colon inhibits cholesterol production in liver (Buttriss & Lunn 2007). Soluble dietary fibers enhance blood glucose control. They lower the rate of glucose absorption into blood stream so decrease the release of insulin to store the glucose into glycogen. This contributes to the treatment of diabetes. Adult with lower fiber diets can develop diabetes more easily than those who consume a lot of fibres (Food and Agriculture Organization nd.).
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.
Viscous fibres reduce glucose absorption in small intestine. Small intestinal contraction creates turbulences and convective currents. These result in fluid circulation and mixing of luminal contents. These brought glucose close to the epithelium. Glucose must then diffuse across the unstirred water layer (UWL). However, viscous fibres resist propulsive contraction so decreases transit time. Thus, inhibits the effects of motility on fluid stirring. This increases thickness of the UWL and reduces transportation of glucose across the epithelium to be absorbed (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 undegraded fibres can trap water easily in colon. Thus lead to a greater bulk and ease the content movement. Dietary fibres reduce transit time by facilitating water movements and contractile activity in the colon. First, the edges of solid particles can easily stimulate mechanoreceptors and alter the contractile pattern of the colon in order to create a greater force of digestion. Besides, undigested starch provides energy for colonic bacterial growth to digest fibres. Thus, some of the faecal bulking effect of dietary fibre is also caused by the increase in starch delivery to the colon (Food and Agriculture Organization nd.).