World Digestive Health Day WDHD – May 29, 2016 DIETARY FIBER; DEFINITION, RECOMMENDATION FOR INTAKE, AND ROLE IN DISEASE PREVENTION AND MANAGEMENT, continued decreases the risk of cardiac events. Improved cardiovascular condition then improves blood pressure regulation. However, short term direct antihypertensive effects of dietary fiber is very controversial. BLOOD GLUCOSE AND INSULIN REGULATION Dietary fiber has been shown to modify postprandial blood glucose and insulin responses.18 Mainly, the viscosity of a fiber affects glucose absorption. When viscous soluble dietary fibers mix with water, it thickens. Intake of soluble dietary fiber increases viscosity of the stomach content, prolongs gastric emptying, increases transit time through the small intestine, and reduces the rate of starch digestion and glucose absorption. Studies have shown that arabinoxylan (AX), β-glucan, fructo-oligosaccharides, and synthetic carbohydrate analogues, such as dextrins, can reduce post-prandial glucose and insulin responses.17 Daily 20 g of fructo-olygosaccaride intake decreases hepatic glucose production.19 Resistant dextrins also decrease postprandial blood glucose concentrations.20 REDUCED TOTAL AND/OR LDL SERUM CHOLESTEROL LEVELS The cholesterol lowering effect of dietary fiber is well-known. Soluble fibers form a viscous layer in the small intestine. This reduces the reabsorption of bile acids and in turn increases the synthesis of bile acids from cholesterol and reduces circulating blood cholesterol.21 The U.S. Food and Drug Administration has concluded that a minimum dose of 3 g/day of oat or barley β-glucan is needed for a beneficial reduction in blood cholesterol levels and subsequent decrease in the risk of coronary heart disease. Psyllium and guar gum have been shown to lower serum cholesterol and LDL in subjects with elevated serum cholesterol, in subjects with non-insulin dependent diabetes, and in subjects receiving lipid-lowering drug therapy. OBESITY Satiation is commonly linked with dietary fiber intake; in particular, β-glucan influences appetite and enhances postprandial satiety. Indigestible dextrins increase satiety and weight reduction. Overall, ingestion of both insoluble and soluble fibers have been linked with positive effects on weight control. The decrease in obesity and metabolic syndrome parallels with the decrease in liver steatosis and steatohepatitis. INCREASING THE FIBER INTAKE When fiber is being increased for a specific purpose, a more careful choice of fiber type is important. If it is desired to lower cholesterol or to improve glycemic control, soluble fiber (such as oat bran or psyllium) should be chosen. If bulking or correction of constipation is desired but the patient suffers from flatulence, insoluble fiber should be used.22 A gradual increase in fiber intake is usually recommended to improve tolerance by minimizing problems of gas and bloating. Large amounts of purified soluble fiber alone may be harmful. High-fiber diet may cause inadequate energy intake. Studies conducted in rats have shown injurious effects of very high fiber diets in the distal colon and enhancement, rather than suppression, of tumorigenesis. This finding may in part relate to massive fermentation of excess fiber in the proximal colon with relatively poor delivery of health-promoting fermentation products to the distal colon. Fiber-induced expansion of the bacterial populations might lead to utilization of alternative metabolic pathways by these populations and these alternative pathways may have more toxic products.22 The production of excess gases from fermentation, with the bulking effects of fiber, can induce bloating. Such symptoms are poorly tolerated by patients with IBS. The colon does adapt to these dietary changes, but this requires several weeks to occur and a gradual introduction is recommended. So enough fiber intake in regular diet is recommended, while too much fiber alone might be hazardous in different aspects.22 SUMMARY Regular fiber intake is recommended for general health. Different fiber types can be useful for the treatment of several gastrointestinal diseases like constipation, diarrhea, IBS, or IBD.23 Patients diagnosed with diabetes, obesity, hyperlipidemia, hypertension, and other cardio-metabolic diseases can get a clinical improvement with soluble fiber intake. Dietary fiber has been demonstrated to play a role in the prevention of colorectal cancer and other neoplastic diseases. REFERENCES 1 Tungland B, Meyer D. Nondigestible oligo- and polysaccharides (dietary fiber): their physiology and role in human health and food. Compr Rev Food Sci Food Saf. 2002; 1(3):90–109. 14 WGO Handbook on DIET AND THE GUT World Digestive Health Day WDHD May 29, 2016
WGO Handbook on Diet and the Gut_2016_Final
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