Encyclopedia
Please note this is a comparison between Version 1 by Emmanuel Anteyi and Version 2 by Bruce Ren.
Nutrition is one of the fundamental approaches to promoting and preventing all kinds of diseases, especially kidney diseases. Dietary fiber forms a significant aspect of renal nutrition in treating chronic kidney disease (CKD). Dietary fiber intake influences the composition and metabolism of the gut microbiome with proven roles in reducing uremic toxin production, preserving kidney function, and retarding the progression of CKD through mechanisms of regulating metabolic, immunological, and inflammatory processes. Understanding dietary fiber’s pathogenesis and mechanistic action in modulating host and microbiome interactions provides a potential adjunct therapeutic target for preventing, controlling, and treating CKD patients.
- chronic kidney disease
- dietary fiber
- gut microbiome
1. Introduction
The increasing role and recognition that lifestyle and dietary habits play in the prevention and promotion of disease and health maintenance continue to stimulate research interest to elucidate the course and pathogenesis of clinical conditions such as cardiovascular diseases, obesity, diabetes, cancer, etc., and kidney diseases [1]. While the health benefits of probiotic intervention in chronic kidney disease (CKD) are well known, recent reviews and data on the role of dietary fiber in promoting kidney health are still evolving [2]. This important role of dietary fiber supplementation or naturally occurring foods in promoting health and disease has increased tremendous research interest in gut microbiome modulation for clinical application and potential therapeutic targets by exploring the gut–kidney axis in CKD [2][3][2,3]. The importance of nutrition to prevent and slow CKD progression has long been recognized, with traditional and primary approaches of dietary treatment comprising predominantly protein restriction, adequate calorie intake, and correction of electrolytes abnormalities [2][4][2,4]. Apart from specific dietary intervention, the role of gut microbiota in reducing uremic toxin production, preserving renal function, and slowing CKD progression has been reported by various studies [4]. High dietary fiber intake modulates the gut microbiome of CKD patients through a complex regulatory effect on host metabolic and immunological processes associated with improved overall health and renal outcomes [4].
2. Health Benefits Effects of Dietary Fiber
The beneficial role of dietary fiber in disease prevention has been partly attributed to its modulation of the gut microbiome in the control of satiety and body weight, regulation of lipid and bile acid metabolism, cancer, and cardiovascular disease risk reduction [5][6][7][12,13,14]. Other known dietary fiber effects on gut microbiota are regulation of inflammation, as observed with decreased C-reactive protein (CRP) marker in an experimental CKD mouse model fed with a high-fat diet following fiber ingestion [8][15]. Dietary fiber regulates glucose and energy homeostasis through the hypothalamic pathway by modulating gut-derived neuropeptides control of gluconeogenesis in the brain and intestines [9][16]. In addition, fiber consumption delays gastric emptying and increases satiating hormones, thereby creating a feeling of fullness mediated by the secretion of incretin gut hormone from intestinal L cells [10][17]. These intestinal incretin hormones are responsible for insulin secretion and glucose homeostasis [10][11][17,18]. Other studies have reported an association between high dietary fiber intake and a reduced risk of developing colorectal cancers [12][19]. All these beneficial effects have been attributed to dietary fiber’s ability to alter gut microbiota in the general population by preventing the occurrence and treating various disease conditions. The challenge with dietary fiber is the lack of a nutritional database to characterize different food sources and quantify fiber classes needed as therapeutic interventions targeting the gut microbiome [13][14][20,21].
The recently updated 2020 KDIGO Clinical Practice Guidelines for Nutrition in CKD recommended adequate intake of dietary fiber from natural sources (vegetables and fruits) due to reported decrease in body weight control, blood pressure, and net acid production in CKD stages 3–5 and improvement in lipid profile of post-transplant recipients [15][22]. Likewise, in diabetic kidney disease, adequate dietary fiber intake in the early stages of CKD was associated with better overall health and renal outcomes [16][23].
The recommended guideline of fiber intake of a healthy diet in the general population is 20–35 g/day, equivalent to 14 g/1000 kcal [13][20]. The USA guideline recommends a mean fiber intake of 17 g/day, but only 5% of the population could meet this recommendation. Beyond the total quantity of fiber, the recommendation did not provide further guidance on specific types or proportions of different fiber-containing food required or needed for adequate intake. Noticing this gap has informed some researchers to suggest that any dietary fiber recommendation should include microbiota-accessible carbohydrates components that can be metabolized by colonic microbiota to derive the health benefits. Microbiota-accessible carbohydrates are carbohydrates, whether from plants or animal tissue sources, resistant to digestion and absorption by the host enzymes, and may also be from mucus secretions in the host’s intestine [14][21].
How dietary fiber contributes to general health has been explained through several mechanisms such as improved colonic transit time, alteration of colon microbial composition and metabolite production, short-chain fatty acids production, and small intestinal lipid and glucose absorption [17][24]. Short-chain fatty acids (SCFA) production reduces inflammation, alters lipid and glucose metabolism that inhibits carcinogenesis, impacts cardiovascular and metabolic disorders, and potentially reduces the risk and progression of CKD [17][18][24,25].
3. Role of Dietary Fiber in CKD Progression
CKD is a global health problem affecting more than 9% of the world population and a high US prevalence of 15%, associated with high healthcare costs, morbidity, and mortality. The increased risk for CKD death has been attributed to chronic inflammation, oxidative stress, malnutrition, high prevalence of hypertension, diabetes, and CVD. A declining kidney function accumulates uremic retention molecules, notably indoxyl sulfate (IS), p-Cresyl sulfate (PCS), trimethylamine-N-Oxide (TMAO), blood urea nitrogen (BUN), and creatinine, known to be associated with a progressive decline of kidney function, mineral bone disorder, CVD, and increased mortality [19][38]. The interaction between gut microbiota and CKD is a bidirectional relationship as CKD causes a shift of healthy gut microbiome composition to a state of imbalance between healthy and pathogenic bacteria termed gut dysbiosis. This gut dysbiosis disrupts intestinal epithelial integrity, enhances inflammatory and immunological processes due to endotoxemia, gut-derived uremic toxins, and acidosis which leads to progression and complications [20][30]. Other contributors to the persistence of dysbiosis include decreased consumption of dietary fibers, frequent antibiotic use, slow colonic transit time, metabolic acidosis, volume overload, intestinal wall edema, and oral iron [20][21][30,39]. An experimental finding of dietary fiber effect on dysbiosis in mouse CKD model fed with high amylose resistant starch diet showed decreased microbial diversity, increased ratio of beneficial Bifidobacteria genera and Bacteroidetes to Firmicutes phyla [21][39]. A similar finding in human CKD stage 3–4 showed increased Bifidobacteria and Lactobacillus species counts after short-term lactulose supplementation [22][40]. Carefully selected dietary fiber administration was found appropriate and effective in reducing uremic toxins in CKD patients with fibers containing resistant starch, arabino-xylo-oligosaccharide, gum acacia, and Xylo-oligosaccharide [23][41]. In another study of hemodialysis (HD) patients, resistant starch supplementation reduced plasma indoxyl sulfate (IS) levels, while an oligofructose enriched inulin diet reduced the serum PCS levels [24][42]. These observations on reducing plasma levels of uremic toxins following interventions with different dietary fiber types were attributed to differences in the effectiveness of modulating gut microbiome to produce sufficient SCFA to restore gut barrier integrity [25][43]. Hence, studies have recommended that CKD patients should increase adequate consumption of dietary multifiber and vegetable-based diet to restore intestinal integrity, improve metabolic profile, prevent comorbidities, and retard CKD progression [26][44]. Due to diet restrictions in CKD patients, supplementary dietary multifiber is a supportive nutritional therapy in all CKD stages to enhance the removal of uremic toxins linked to cardiovascular complications [27][45]. High fiber intake as a recommended renal diet in CKD remains a challenge due to concerns of high potassium and phosphorus levels. To overcome these fears, fiber from natural foods sources (fruits, vegetables, whole grains) as plant-based diets should be preferred due to better nutrient composition and relatively lower bioavailability of potassium and phosphorus [28][46].
