Dietary fiber intake provides many health benefits. However, average fiber intakes for US children and adults are less than half of the recommended levels. Individuals with high intakes of dietary fiber appear to be at significantly lower risk for developing coronary heart disease, stroke, hypertension, diabetes, obesity, and certain gastrointestinal diseases. Increasing fiber intake lowers blood pressure and serum cholesterol levels. Increased intake of soluble fiber improves glycemia and insulin sensitivity in non-diabetic and diabetic individuals. Fiber supplementation in obese individuals significantly enhances weight loss. Increased fiber intake benefits a number of gastrointestinal disorders including the following: gastroesophageal reflux disease, duodenal ulcer, diverticulitis, constipation, and hemorrhoids. Prebiotic fibers appear to enhance immune function. Dietary fiber intake provides similar benefits for children as for adults. The recommended dietary fiber intakes for children and adults are 14 g/1000 kcal. More effective communication and consumer education is required to enhance fiber consumption from foods or supplements.

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Health benefits of dietary fiber

The gastrointestinal tract is subjected to enormous and continual foreign antigenic stimuli from food and microbes. This organ must integrate complex interactions among diet, external pathogens, and local immunological and non-immunological processes. It is critical that protective immune responses are made to potential pathogens, while hypersensitivity reactions to dietary antigens are minimised. There is increasing evidence that fermentable dietary fibres and the newly described prebiotics can modulate various properties of the immune system, including those of the gut-associated lymphoid tissues (GALT). This paper reviews evidence for the immune-enhancing effects of dietary fibres. Changes in the intestinal microflora that occur with the consumption of prebiotic fibres may potentially mediate immune changes via: the direct contact of lactic acid bacteria or bacterial products (cell wall or cytoplasmic components) with immune cells in the intestine; the production of short-chain fatty acids from fibre fermentation; or by changes in mucin production. Although further work is needed to better define the changes, mechanisms for immunomodulation, and the ultimate impact on immune health, there is convincing preliminary data to suggest that the consumption of prebiotics can modulate immune parameters in GALT, secondary lymphoid tissues and peripheral circulation. Future protocols on the physiological impact of consuming prebiotics should be designed to include assessments of the gut microflora, gut physiology and the function and composition of the various regions of GALT.

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The immune-enhancing effects of dietary fibres and prebiotics.

Background
A large body of literature suggests that certain polysaccharides affect immune system function. Much of this literature, however, consists of in vitro studies or studies in which polysaccharides were injected. Their immunologic effects following oral administration is less clear. The purpose of this systematic review was to consolidate and evaluate the available data regarding the specific immunologic effects of dietary polysaccharides.

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Immunomodulatory dietary polysaccharides: a systematic review of the literature.

The use of natural honey (NH) as a nutraceutical agent is associated with nutritional benefits and therapeutic promises. NH is widely accepted as food and medicine by all generations, traditions and civilizations, both ancient and modern. The nutritional profiles, including its use in infant and children feeding reported in different literatures as well as health indices and biomarkers observed by various researchers are illustrated in this manuscript. The review documents folk medicine, experimentation with animal models, and orthodox medical practices shown by clinical trials. This covers virtually all human organs and body systems extensively studied by different workers. The sources and adverse effects of NH contamination, as well as the preventive methods are identified. This could promote the availability of residue free honey and a wholesome natural product for domestic consumption and international market. This could also help to prevent health problems associated with NH poisoning. In addition, apicultural practices and the economic importance of honey are well documented. This report also includes information about a relatively unknown and uncommon South American stingless bee species. We concluded this review by identifying important roles for Ethno-entomologists, other Scientists and Apiculturists in the development of stingless bees to boost honey production, consumption and economic earnings.

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Nutraceutical values of natural honey and its contribution to human health and wealth

Barley, like oats, is a rich source of the soluble fibre beta-glucan, which has been shown to significantly lower LDL-cholesterol (LDL-C). However, barley foods have been less widely studied. Therefore, we evaluated the LDL-C-lowering effect of a concentrated barley beta-glucan (BBG) extract as a vehicle to deliver this potential health benefit of barley. In a 10-week blinded controlled study, subjects were randomized to one of four treatment groups or control. Treatment groups included either high molecular weight (HMW) or low molecular weight (LMW) BBG at both 3 and 5 g doses. Treatment was delivered twice per day with meals in the form of two functional food products: a ready-to-eat cereal and a reduced-calorie fruit juice beverage. Levels of total cholesterol, LDL-C, HDL-cholesterol (HDL-C), and TAG were determined at baseline and after 6 weeks of treatment. The study group comprised 155 subjects. All treatments were well tolerated and after 6 weeks of treatment the mean LDL-C levels fell by 15 % in the 5 g HMW group, 13 % in the 5 g LMW group and 9 % in both the 3 g/d groups, versus baseline. Similar results were observed for total cholesterol. HDL-C levels were unchanged by treatment. Concentrated BBG significantly improves LDL-C and total cholesterol among moderately dyslipidaemic subjects. Food products containing concentrated BBG should be considered an effective option for improving blood lipids.

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The effects of concentrated barley β-glucan on blood lipids in a population of hypercholesterolaemic men and women

Eight-month-old Sprague-Dawley rats were fed on diets containing dietary fiber at the 5% level for 3 weeks to examine the effect on the lipid metabolism and immune function. Among cellulose, guar gum, partially hydrolyzed guar gum (PHGG), glucomannan and highly methoxylated pectin, guar gum induced a significant decrease in the food intake and weight gain, as well as a significant increase in the liver weight. In addition, the epidydimal adipose tissue weight of the rats fed on PHGG was significantly higher than that of the rats fed on cellulose. There was no significant effect on the serum lipid levels, but the serum IgG level of the rats fed on guar gum was significantly lower than that of the rats fed on cellulose. The IgA and IgG productivity in mesenteric lymph node (MLN) lymphocytes was significantly higher in the rats fed on guar gum, glucomannan and pectin than in those fed on cellulose, while the effect on Ig productivity in spleen lymphocytes was not as marked. In addition, only guar gum induced a significant increase of IgM productivity in MLN lymphocytes when compared to the cellulose group. These results suggest that enhancement of the immune function by dietary fiber is mainly expressed in the gut immune system.

Effect of Dietary Fiber on the Lipid Metabolism and Immune Function of Aged Sprague-Dawley Rats

The dietary effect of the water-soluble dietary fibers (WSDF), guar gum, partially hydrolyzed guar gum (PHGG), glucomannan, highly methoxylated (HM) pectin, on the serum lipid level and immunoglobulin (Ig) production of Sprague-Dawley rats was compared with that of water-insoluble cellulose. Although serum total cholesterol and triglyceride levels were significantly lower in the rats fed with WSDF than in those fed with cellulose, a decrease in the level of phospholipids was only observed in the rats that had been fed on guar gum or glucomannan. In addition, all WSDF feeding enhanced IgA productivity in the spleen and mesenteric lymph node lymphocytes, although the increase in serum IgA level was only observed in the rats fed on WSDF, and not on PHGG. When mesenteric lymph node lymphocytes were cultured in the presence of various concentrations of guar gum or glucomannan, no significant increase in Ig production was apparent. These data suggest that WSDF indirectly enhanced the Ig production of lymphocytes, and that serum lipid reduction and IgA production-enhancing activities of WSDF were dependent on their molecular sizes.

https://www.tandfonline.com/doi/pdf/10.1271/bbb.63.2163

Soichi Mamiya

Papers

Effect of Dietary Fiber on the Lipid Metabolism and Immune Function of Aged Sprague-Dawley Rats

Dietary Effect of Guar Gum and its Partially Hydrolyzed Product on the Lipid Metabolism and Immune Function of Sprague-Dawley Rats