膳食纤维与肠道健康

由于食物的精加工和生活习惯改变,运动减少,现代人的肠道健康状况下降,肠道疾病发病率不断增加,这已经影响到人们的身体健康和日常生活。肠道疾病的发生多与有毒有害物质在肠道内过久滞留,引起肠道环境改变恶化,进而损伤肠道细胞并引发各类炎症有关。本研究综述了59篇有关于膳食纤维和肠道相互作用的文献。研究表明摄入膳食纤维有助于促进肠道蠕动,保持大便顺畅,防止便秘,清除肠道内的有毒有害物质,保持肠道清洁和促进肠道内的益生菌生长等功效。而且,膳食纤维对肠易激综合征,炎症性肠病和肠癌等常见肠道疾病也具有一定的预防和治疗作用。综上,膳食纤维的摄人有益于保持肠道正常生理功能,修复和改善受损肠道环境,对于维护肠道健康有重要意义。     

Dietary fiber and the glycemic response

Addition of purified fiber to carbohydrate test meals has been shown to flatten the glycemic response in both normal and diabetic volunteers, reduce the insulin requirement in patients on the artificial pancreas and in the longer term reduce urinary glucose loss and improve diabetes control. In the context of high fiber-high carbohydrate diets these findings have had a major impact in influencing recommendations for the dietary management of diabetes internationally. The mechanism of action appears in part to be due to the effect of fiber in slowing absorption rather than by increasing colonic losses of carbohydrate. Consequently postprandial GIP and insulin levels are reduced and the more viscous purified fibers (e.g., guar and pectin) appear most effective. In addition it has been suggested that colonic fermentation products of fiber may enhance glucose utilization. More recently it has become clear that many aspects of carbohydrate foods (food form, antinutrients, etc.) in addition to fiber may influence the rate of digestion and has led to a classification especially of starchy foods in terms of glycemic index to define the degree to which equicarbohydrate portions of different foods raise the blood glucose. Use of such data may maximize the effectiveness of high carbohydrate and high fiber diets in the management of diabetes and related disorders.     

Dietary fiber, lipid metabolism, and atherosclerosis

Despite the physiochemical complexity of dietary fibers (plant cell walls) and their individual components, there is substantial epidemiologic, clinical, and experimental evidence that these dietary components may have a role in modifying certain risk factors in coronary heart disease. Particulate fibers, such as wheat bran, do not appear to significantly alter plasma lipids or lipoprotein distributions in humans, or the atherogenicity of diets in experimental animals. Dietary fibers found in fruits, legumes, and vegetables, in contrast, show more definitive responses. Among the fiber isolates, the gelling and mucilaginous fibers, such as pectins and guar gum, predictably decrease circulating lipids in humans and animals and increase excretion of fecal metabolites of cholesterol, the bile acids. These fibers and fiber components can be shown to influence luminal solubility of lipids and the extent of lymphatic absorption of both cholesterol and triglyceride. In addition, these same fibers are effective in reducing postprandial levels of glucose, insulin, and other hormones. These direct effects on lipid absorption, and secondary effects of glucose and insulin on hepatic and peripheral lipoprotein metabolism, can account for many of the hypolipidemic responses to specific dietary fibers or their components, and may be of long-term consequence in coronary heart disease.     

Dietary fiber decreases cholesterol and phospholipid synthesis in rat intestine

The effects of fiber ingestion on the incorporation of oleic acid into triglyceride and lecithin, acetate incorporation into cholesterol, and monosaccharide and amino acid transport were determined in rat intestine. Prolonged pectin (10% by weight) ingestion caused a decrease in jejunal and ileal cholesterol synthesis (33% and 52%, respectively). Pectin ingestion reduced cholesterol synthesis by 60% in ileal crypt cells, but did not affect cholesterol synthesis in the jejunal or ileal villus cells or in jejunal crypt cells. Cholesterol synthesis in isolated crypt cells was markedly less than in isolated villus cells. Prolonged ingestion of a fiber-free diet supplemented with either cellulose or pectin (10% and 5% by weight, respectively) decreased jejunal lecithin glucose and leucine absorption but did not affect jejunal triglyceride synthesis.     

Dietary fiber components: relationship to the rate and extent of ruminal digestion

A mathematical model can serve as a useful reference for describing the mechanisms involved in digestion and for discussing the factors that influence the rate and extent of ruminal digestion. Ruminal digestion can be divided into four components: digestion rate, digestion lag, potential extent of digestion, and passage rate. Each component affects the apparent extent of digestion in a distinct manner and is influenced by separate factors. Digestion rate is directly related to apparent extent of digestion. It is not influenced by chemical entities presently being measured, but may be related to the morphological, crystalline, or physical nature of fiber. It may also be influenced by factors that inhibit or stimulate ruman microbial growth and their fiber-degrading enzymes. Digestion lag is inversely related to apparent extent of digestion; however, factors influencing it are poorly defined. The may include factors affecting microbial populations and their attachment to fiber prior to digestion; or the digestion lag may be related to the chemical or physical alteration of fiber that must occur before digestion can begin. The potential extent of digestion is directly related to apparent extent of digestion and is influenced by plant fiber composition, primarily. Lignin, and possibly silica, functions to limit the potential extent of digestion. Rate of passage essentially competes with rate of digestion for fiber particles as they pass through the rumen; therefore it is inversely related to the apparent extent of digestion. Passage rate is associated with feed intake level and particle size, although other factors such as type of diet and animal physiology may be important.     

Dietary sugar beet fiber ameliorates diarrhea as an acute gamma-radiation injury in rats

Gamma radiation induces diarrhea as an acute injury. We have studied whether ingestion of sugar beet fiber influences radiation-induced diarrhea. Abdominal irradiation with gamma rays induced diarrhea in male Wistar/ST rats from 2 to 7 days after a single sublethal dose. The body weight of the irradiated rats was decreased temporarily at 4 days after irradiation regardless of the ingestion of sugar beet fiber. At day 8, it returned to almost the same level as that of unirradiated rats. A change in daily food intake resulted in a pattern similar to that for body weight. Dietary sugar beet fiber had little significant effect on the changes in body weight and daily food intake, and its ingestion significantly decreased gamma-ray-induced diarrhea. Changes in biochemical and histological parameters in intestinal mucosa (small intestine, cecum and colon) were not greatly influenced by the ingestion of sugar beet fiber through the periods of diarrhea. It was concluded that dietary sugar beet fiber ameliorated the diarrhea induced by abdominal irradiation. We suggest that the inhibitory effect of the ingestion of sugar beet fiber is due to its effects on the luminal environment, such as support for bacterial function in the luminal contents in the colon of animals that ingest sugar beet fiber.     

Dietary fiber decreases colonic epithelial cell proliferation and protein synthetic rates in human subjects

Although it has been proposed that high fiber consumption can prevent proliferative diseases of the colon, the clinical data to support this hypothesis have been inconsistent. To provide a more robust measure of the effects of fiber on colonic mucosal growth than previous studies, we evaluated both cell proliferation and colonic mucosal protein synthesis in nine healthy volunteers after they consumed a typical Western diet (<20 g fiber/day) or a Western diet supplemented with wheat bran (24 g/day) in a randomized crossover design. Biopsies taken from the sigmoid colon were used to assess mucosal proliferation by determining proliferating cell nuclear antigen (PCNA) in crypt cells and to assess mucosal protein synthetic rate using stable isotopically labeled leucine infusion. Fiber supplementation produced a 12% decrease in labeling index (%crypt cells stained with PCNA) (P < 0.001) and an 11% decrease in mucosal protein fractional synthetic rate (FSR; P < 0.05). Moreover, mucosal protein FSR correlated directly with labeling index (r2= 0.22, P < 0.05). These data demonstrate that increased wheat bran consumption decreases colonic mucosal proliferation and support the potential importance of dietary fiber in preventing proliferative diseases of the colon.     

Dietary fiber and lipid peroxidation: effect of dietary fiber on levels of lipids and lipid peroxides in high fat diet.

Effect of feeding coconut and blackgram fiber isolated as neutral detergent fiber (NDF) on the levels of lipids and lipid peroxides was studied in rats given a high fat diet. Concentration of cholesterol, free falty acid and phospholipids showed significant decrease in the serum, liver aorta and intestine of coconut and blackgram fiber groups. Concentration of malondialdehyde (MDA) and conjugated dienes was significantly decreased in liver and intestine of both fiber groups, while hydroperoxides showed significant increase in liver and heart of both the fiber groups. SOD and catalase activity was found to be increased in liver, intestine, heart proximal colon and distal colon of both the fiber groups. Serum ceruloplasmin levels showed a slight increase in animals fed coconut and blackgram fiber groups. Glutathione levels in liver, intestine proximal colon, distal colon and heart also showed a significant decrease in the animals of both the fiber groups.     

Review: Dietary fiber utilization and its effects on physiological functions and gut health of swine

Although dietary fiber (DF) negatively affects energy and nutrient digestibility, there is growing interest for the inclusion of its fermentable fraction in pig diets due to their functional properties and potential health benefits beyond supplying energy to the animals. This paper reviews some of the relevant information available on the role of different types of DF on digestion of nutrients in different sections of the gut, the fermentation process and its influence on gut environment, especially production and utilization of metabolites, microbial community and gut health of swine. Focus has been given on DF from feed ingredients (grains and coproducts) commonly used in pig diets. Some information on the role DF in purified form in comparison with DF in whole matrix of feed ingredients is also presented. First, composition and fractions of DF in different feed ingredients are briefly reviewed. Then, roles of different fractions of DF on digestion characteristics and physiological functions in the gastrointestinal tract (GIT) are presented. Specific roles of different fractions of DF on fermentation characteristics and their effects on production and utilization of metabolites in the GIT have been discussed. In addition, roles of DF fermentation on metabolic activity and microbial community in the intestine and their effects on intestinal health are reviewed and discussed. Evidence presented in this review indicates that there is wide variation in the composition and content of DF among feed ingredients, thereby their physico-chemical properties in the GIT of swine. These variations, in turn, affect the digestion and fermentation characteristics in the GIT of swine. Digestibility of DF from different feed ingredients is more variable and lower than that of other nutrients like starch, sugars, fat and CP. Soluble fractions of DF are fermented faster, produce higher amounts of volatile fatty acid than insoluble fractions, and favors growth of beneficial microbiota. Thus, selective inclusion of DF in diets can be used as a nutritional strategy to optimize the intestinal health of pigs, despite its lower digestibility and consequential negative effect on digestibility of other nutrients.     

Dietary modulation of experimental neoplastic development: role of fat and fiber content and calorie intake

Cancer is still one of the major causes of death in the industrialized countries but locally prevailing lifestyles may dictate the kinds of cancer seen among populations of different geographical areas. Dietary habits and, in particular, the nature and/or the amount of fat, calorie and/or vegetable fiber which are consumed in these countries are among the most frequently quoted etiological factors which may account for this situation. Epidemiological and experimental evidence has accumulated which, even though it can be used to support these conclusions, is still a matter of considerable debate.Modulation of neoplastic development is a concept which has been elaborated to overcome the fact that many experimental observations are not really taken into consideration by the classical 2-step theory of carcinogenesis. It is defined as the effect of any treatment which given before, during or after the initiation of a full carcinogenic process modifies the pattern of neoplastic development as evaluated by the kinetics of appearance, the incidence and/or the yield of histologically characterized malignant tumors. It is said to be positive or negative depending on whether it accelerates or slows down the process and increases or decreases the yield of malignant tumors respectively.From a review of the available experimental data, it is concluded that fat per se has, most probably, no modulating effect but that unbalanced diets rich in lipids could act as a positive modulator of chemically induced carcinogenesis by virtue of their capacity to cause a break in metabolic and proliferative homeostasis; that vegetable fibers as well as restriction in calorie intake could act as negative modulators of the same process because they could restore or help restore this homeostasis. It is thus proposed that to maintain dietary balance either by increasing fiber and/or by reducing total calorie intake is the most effective way to negatively modulate chemically induced carcinogenesis in experimental animals. To make the same recommendation to humans could most probably help preventing major cancers like breast and colon cancers.     

Dietary fiber inhibits the incidence of hepatic metastasis with the anti-oxidant activity and portal scavenging functions

Dietary fiber is described as the proportion of plant foods not digested in the human small intestine. Among the various kinds of pectin, apple pectin exerts a bacteriostatic action and therefore may change the composition of the intestinal flora. The diet supplemented with 20% apple pectin significantly decreased the number and the incidence of AOM-induced colon tumors in rats. The prostaglandin E2 (PGE2) level in the distal colonic mucosa and blood of portal vein was lower in rats fed 20% pectin than those fed the basal diet. The ability of apple pectin to decrease PGE2 was dose-dependent and those results suggest an anti-inflammatory effect in the bowel. Rats fed apple pectin showed a significantly lower incidence of hepatic metastasis than those fed the basal diet. To determine whether the anti-inflammatory effect of Lactobacillus on hepatic metastasis model same as apple pectin, Lactobacillus casei was selected. Metastatic nodules were significantly reduced, especially in the group receiving pretreatment. Apple pectic oligosaccharides with small molecular weights showed highly inhibitory effects on hypoxanthin-xanthin oxidase and ferrous sulfate-hydrogen peroxide. The scavenging activity of apple pectic oligosaccharides was suitable and accelerated at high temperatures (120 degrees C, 30 min.). Apple pectin and Lactobacillus have a scavenger effect in the intestinal digestion and portal circulation system as an anti-inflammatory food and have very important function for the prevention of hepatic metastasis.     

Dietary fiber, carbohydrate quality and quantity, and mortality risk of individuals with diabetes mellitus

Background

Dietary fiber, carbohydrate quality and quantity are associated with mortality risk in the general population. Whether this is also the case among diabetes patients is unknown.

Objective

To assess the associations of dietary fiber, glycemic load, glycemic index, carbohydrate, sugar, and starch intake with mortality risk in individuals with diabetes.

Methods

This study was a prospective cohort study among 6,192 individuals with confirmed diabetes mellitus (mean age of 57.4 years, and median diabetes duration of 4.4 years at baseline) from the European Prospective Investigation into Cancer and Nutrition (EPIC). Dietary intake was assessed at baseline (1992–2000) with validated dietary questionnaires. Cox proportional hazards analysis was performed to estimate hazard ratios (HRs) for all-cause and cardiovascular mortality, while adjusting for CVD-related, diabetes-related, and nutritional factors.

Results

During a median follow-up of 9.2 y, 791 deaths were recorded, 306 due to CVD. Dietary fiber was inversely associated with all-cause mortality risk (adjusted HR per SD increase, 0.83 [95% CI, 0.75–0.91]) and CVD mortality risk (0.76[0.64–0.89]). No significant associations were observed for glycemic load, glycemic index, carbohydrate, sugar, or starch. Glycemic load (1.42[1.07–1.88]), carbohydrate (1.67[1.18–2.37]) and sugar intake (1.53[1.12–2.09]) were associated with an increased total mortality risk among normal weight individuals (BMI≤25 kg/m²; 22% of study population) but not among overweight individuals (P interaction≤0.04). These associations became stronger after exclusion of energy misreporters.

Conclusions

High fiber intake was associated with a decreased mortality risk. High glycemic load, carbohydrate and sugar intake were associated with an increased mortality risk in normal weight individuals with diabetes.     

Dietary modulation of experimental neoplastic development: role of fat and fiber content and calorie intake.

Cancer is still one of the major causes of death in the industrialized countries but locally prevailing lifestyles may dictate the kinds of cancer seen among populations of different geographical areas. Dietary habits and, in particular, the nature and/or the amount of fat, calorie and/or vegetable fiber which are consumed in these countries are among the most frequently quoted etiological factors which may account for this situation. Epidemiological and experimental evidence has accumulated which, even though it can be used to support these conclusions, is still a matter of considerable debate. Modulation of neoplastic development is a concept which has been elaborated to overcome the fact that many experimental observations are not really taken into consideration by the classical 2-step theory of carcinogenesis. It is defined as the effect of any treatment which given before, during or after the initiation of a full carcinogenic process modifies the pattern of neoplastic development as evaluated by the kinetics of appearance, the incidence and/or the yield of histologically characterized malignant tumors. It is said to be positive or negative depending on whether it accelerates or slows down the process and increases or decreases the yield of malignant tumors respectively. From a review of the available experimental data, it is concluded that fat per se has, most probably, no modulating effect but that unbalanced diets rich in lipids could act as a positive modulator of chemically induced carcinogenesis by virtue of their capacity to cause a break in metabolic and proliferative homeostasis; that vegetable fibers as well as restriction in calorie intake could act as negative modulators of the same process because they could restore or help restore this homeostasis. It is thus proposed that to maintain dietary balance either by increasing fiber and/or by reducing total calorie intake is the most effective way to negatively modulate chemically induced carcinogenesis in experimental animals. To make the same recommendation to humans could most probably help preventing major cancers like breast and colon cancers.