World Digestive Health Day WDHD – May 29, 2016 DIETARY FIBER; DEFINITION, RECOMMENDATION FOR INTAKE, AND ROLE IN DISEASE PREVENTION AND MANAGEMENT, continued transit time, thereby helping in the prevention and treatment of constipation.10 Fibers in diet are effective promoters of normal laxation, as are psyllium seed husk and methylcellulose in the form of supplements. Beside insoluble dietary fibers, soluble fructans have been shown to have a beneficial effect in the large intestine.11 Diverticular disease is one of the most common GI diseases. A generous intake of dietary fiber is considered to be protective, ameliorative, and preventive of recurrences of diverticular disease.10,11 Similarly, several trials have shown that supplementation of some types of dietary fiber can prolong remission during the course of the inflammatory bowel disease (IBD). These effects are primarily related with increased luminal production of immunomodulator short chain fatty acids (SCFA). There is general agreement that if there is no intestinal strictures and the patient is in remission, dietary fiber consumption should not be limited in IBD. GUT MICROBIOTA AND PREBIOTIC EFFECTS Dysbiosis in gut microbiota is associated with the pathogenesis of many diseases, including infectious diseases, allergy, IBD, obesity, diabetes, liver disease, and colon cancer.12 Gut microbiota can be affected by many factors, including medications, stress, and diet. Dietary fibers acting as a prebiotic selectively enrich beneficial gut bacteria, mainly bifidobacteria and/or lactobacillus.2 Prebiotics that include fructo-oligosaccharides, oligofructose, and inulin were shown to increase the concentrations of bifidobacteria and or lactobacillus species in the gut. Bacterial fermentation of the ingested fiber in the colon produces SCFAs, primarily acetic, propionic, and butyric acid. These SCFAs provide various health benefits to the host, such as: supplying fuel to colonocytes; regulating proliferation and differentiation of epithelial cells; increasing colonic blood flow, reducing colonic pH; stimulating pancreatic secretions, other gut hormones, and the autonomic nervous system; promoting sodium and water absorption; and regulating gut motility.12 MINERAL AND MICRONUTRIENT ABSORPTION There are concerns that micronutrient absorption may be adversely impacted by diets high in fiber. Diet high in insoluble fiber is not associated with poorer micronutrient status in healthy population consuming their usual diet.13 On the other hand, certain fiber types play a beneficial role in mineral and micronutrient absorption. Highly fermentable fibers have resulted in improved metabolic absorption of certain minerals, such as calcium, magnesium, and iron. Fermentation of fiber by colonic microbiota and subsequent SCFA production leads to reduction in luminal pH. The SCFA and lower pH may, in turn, dissolve insoluble mineral salts, especially calcium, magnesium, and iron, and increase their absorption.1 CANCER PREVENTION Recent studies support this inverse relationship between dietary fiber and the development of several types of cancers, including colorectal, small intestine, oral, esophageal, larynx, and breast.14 Cellulose is the major type of fiber that has been shown to reduce risk of colon cancer. This effect is related to decrease in colon transit time and excretion of mutagens, as well as decrease in fecal bile acid concentration.15 Pectin and pectic oligosaccharides were shown to induce apoptosis in human colonic adenocarcinoma cells in vitro.16 Although the mechanisms responsible are still unclear, several explanations have been proposed. First, dietary fibers are fermented to produce SCFAs, which have anti-carcinogenic properties. Second, there is less contact time between potential carcinogens and mucosal cells. Third, dietary fiber increases the binding between bile acids and carcinogens. Fourth, increased intake of dietary fiber yields increased levels of antioxidants. Fifth, fibers may decrease estrogen absorption in the intestines.14,15 Dietary fiber is also preventive against esophageal carcinogenesis, most notably esophageal adenocarcinoma by modification of gastroesophageal reflux and weight control. CARDIAC DISEASE Cardiac disease is attributed to lifestyle, such as diet, physical activity, and cigarette abuse. High levels of dietary fiber intake are associated with significantly lower prevalence rates for cardiac disease, stroke, and peripheral vascular disease.2 A pooled analysis of 10 prospective cohort studies indicated that every 10 g/d increase of dietary fiber was associated with decreased risk of coronary events and coronary death by 14 and 27 %, respectively.17 Control and treatment of cardiac risk factors by high fiber intake decreases the prevalence of cardiac disease. Soluble fibers have been shown to increase the rate of bile excretion, therefore reducing serum total and LDL cholesterol. Dietary fiber regulates energy intake and blood glucose, thus enhancing weight loss. Dietary fiber has been shown to decrease pro-inflammatory cytokines, such as interleukin-18 which may have an effect on plaque stability. By controlling all of these risk factors, enough fiber intake World Digestive Health Day WDHD May 29, 2016 WGO Handbook on DIET AND THE GUT 13
WGO Handbook on Diet and the Gut_2016_Final
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