Soluble and Insoluble Fibers Lecture Notes PDF

Soluble fibers Physiological effects: 1) Reduced nutrient absorption: The gel mixture formed by DFs can cholesterol, bile acids, and glucose reducing their absorption from GIT. 2) Extended gastric emptying: The increased viscosity and gel formation slow gastric emptying, enhancing satiety,...

Soluble fibers Physiological effects: 1) Reduced nutrient absorption: The gel mixture formed by DFs can cholesterol, bile acids, and glucose reducing their absorption from GIT. 2) Extended gastric emptying: The increased viscosity and gel formation slow gastric emptying, enhancing satiety, and potentially aiding in weight management by reducing overall caloric intake. This effect can be particularly useful for obese individuals. 3) Water Absorption and Expansion: - Soluble fibers absorb water and expand, increasing the volume and viscosity of digestive contents, which aids in digestive comfort and nutrient regulation.  insoluble fibers They do not gel-like masses and are less fermentable by gut bacteria. Common sources: include cellulose and lignin, found in foods like whole grains, vegetables, and certain seeds. Limited Fermentation and Bulk Addition: - Although minimally fermented by colonic microbes, insoluble fibers contribute bulk to the stool, promoting quicker passage through the stomach and intestines, which can help with regularity.  insoluble fibers Physiological effects: 1) Enhanced Fullness: By adding volume to the stomach contents, insoluble fibers can contribute to feelings of fullness and satisfaction. 2) Shortened Transit Time: Insoluble fibers add bulk, aiding in the rapid transit of food through the digestive system, promoting regularity and supporting gut health. 3) Health Benefits of SCFAs: While they are not preferred by probiotics, insoluble fibers are partially fermented into SCFAs, which provide additional health benefits. Comparison between soluble and insoluble fibers P.O.C Soluble fibers Insoluble fibers Viscosity Increased No effect Gel Forms No gel formation Probiotic Food for good bacteria Not utilized by probiotics Fermentation Promote fermentation Less fermentable SCFAs Promote SCFAs SCFAs Water retention High Fibro-protein complex Transit time (gastric Increase Decrease emptying time) ↑Stool weight ↑ bacterial mass & ↑water Presence of fibers itself content  Fermentability - Fermentable fibers are those that can Characteristics Fiber Food be metabolized by colonic bacteria, component sources supporting gut health and beneficial Cellulose Plants metabolic byproducts. (vegetables, - In general, soluble fibers are more Water sugar beet) completed fermented compared to insoluble/ less insoluble fibers. Hemicellulos Cereal grains fermentable e - Nearly all DFs undergo some degree of fermentation in colon. Lignin Woody plants - Variation in Fermentation: The rate and Water Pectin Citrus fruits extent of fermentation differ among fiber types. Each type of fiber also varies in soluble/more the amount and ratio of short-chain fatty fermentable Gums Guar gum acids (SCFAs) it produces, as well as the rate at which these SCFAs are Beta-glucan Barely and generated. oat endosperms  Viscosity ❑ Definition: - Refers to the gel-forming ability of fibers when they interact with water in the digestive tract. This characteristic is largely seen in soluble fibers, although some soluble fibers are not viscous, and certain insoluble fibers can still be fermentable. - Factors Influencing Viscosity: 1- Molecular Weight and Concentration: A fiber’s molecular weight and concentration are positively correlated with its viscosity; higher weight and concentration often result in increased viscosity. 2- Solubility: Soluble fibers, in general, exhibit higher viscosity than insoluble fibers. However, there are exceptions, like partially hydrolyzed guar gum and acacia gum, which are soluble but not viscous.  Viscosity ❑Physiological implications of viscous fibers: 1) Enhance satiety: - Viscous fibers form a gel that expands in the stomach, increasing fullness and potentially aiding in weight management. 2) Slow down gastric emptying: - By thickening digestive contents, viscous fibers slow the emptying rate of the stomach, leading to extended digestion times. 3) Lowered post-prandial glycemia and hyperlipidemia: - By delaying the absorption of glucose and lipids, viscous fibers help moderate post-meal blood sugar levels and reduce fat absorption, benefiting metabolic health.  Viscosity - Mechanisms Behind Viscosity-Related Benefits: 1) Reduced Nutrient Diffusion: Viscous fibers increase the thickness of the unstirred water layer on the intestinal mucosa, slowing the diffusion of nutrients like glucose, leading to a gradual release into the bloodstream and a lowered post- prandial glucose spike. 2) Impaired Lipid Emulsification: Increased viscosity can interfere with the emulsification of lipids in the small intestine by reducing the formation and size of lipid droplets. This mechanism limits the bioavailability of lipophilic compounds, potentially moderating lipid absorption and post-prandial lipid levels. Water binding and hydration capacity of dietary fibers - Dietary fibers (DF) are recognized for their significant water-binding abilities, with soluble fibers generally demonstrating a much higher water-holding capacity than insoluble ones. - This hydration property include the swelling capacity, where fibers retain water, either between the DF particles (extra-particulate water) & within fibers structure (intra-particulate water).  Binding and interaction properties of dietary fibers polysaccharides Dietary fibers can non-covalently bind, adsorb, or entrap other nutrients and compounds during digestion. Key binding interaction include: - Binding with bile acids. - Binding with phenolic compounds. - Binding with minerals. - Binding directly with enzyme. 1) Binding with bile acids: - Bile acid function: Bile acids, synthesized from cholesterol in liver, are released into small intestine with bile during digestion. They play a role in emulsifying dietary fats, formation of mixed micelles, enabling proper digestion and absorption of lipophilic compounds.  Binding and interaction properties of dietary fibers polysaccharides ❑Physiological implications of DF-BA interactions: When DFs bind with bile acids, they form a complex that prevents these bile acid from being reabsorbed and recycled in small intestine. As result, the fiber-bound bile acids continue through the digestive system and are eventually excreted in feces. Certain dietary fibers like pectin, β-glucan, and guar gum, have ability to bind bile acids in small intestine, reducing their reabsorption in the small intestine. To compensate, the liver converts endogenous cholesterol into bile acids, which can lower blood cholesterol. This interaction also decreases the availability of bile acids as emulsifiers, which may affect lipid digestion and the absorption of certain fat-soluble nutrients, potentially reducing circulating triglyceride levels.  Binding and interaction properties of dietary fibers polysaccharides 2) Binding with phenolic compounds (PCs) such as ferulic acid ❑ Type of interactions: - DFs can bind with PCs through multiple types of non-covalent bonds these interactions include hydrogen bonding, electrostatic interaction, and hydrophobic interactions. - Among various DFs, Cellulose appears to have higher affinity for phenolic acids, such as ferulic acid, compared to pectin.  Binding and interaction properties of dietary fibers polysaccharides ❑Physiological implications of DF-PCs interactions: 1) Modulation of PC bioavailability: When PCs are bound to DFs will escape absorption in small intestine, allowing them to travel to large intestine (colon). Here, DFs undergo fermentation by colonic microbiota, which can then release bound PCs, making them available for absorption in their modified or unmodified forms in the colon. This delayed absorption may benefit overall gut health and the body’s antioxidant defense systems.  Binding and interaction properties of dietary fibers polysaccharides 2) Protection of labile phenolic compounds: Many phenolic compounds, such as anthocyanins, are highly susceptible to degradation in the harsh environments of the upper GIT (e.g., acidic pH in the stomach, enzymatic activity in the small intestine). When bound to DF, these compounds are protected as they move through GIT, preserving their functional structure until reach the colon, where fermentation may release them. This fiber binding serves as a protective mechanism, similar to the stabilizing effects seen with protein-PC interactions.  Binding and interaction properties of dietary fibers polysaccharides 3) Enhanced antioxidant activity in the colon: As PCs remain longer in the large intestine due to DF binding, they can play a critical role in maintaining a reducing, or antioxidant- rich, environment in the colon. PCs act as potent radical scavengers, helping to neutralize reactive oxygen species (ROS) and other radicals that could otherwise damage colonic cells or lead to inflammatory responses. This antioxidant effect may contribute to long-term colon health and potentially reduce the risk of certain diseases.  Binding and interaction properties of dietary fibers polysaccharides 3) Binding of dietary fibers (DFS) with minerals: Dietary fibers have the capacity to bind with minerals through specific functional groups includes carboxylic, sulfate, and amino. Types of interactions between DFs and minerals: By electrostatic interactions - These interactions are stronger with divalent cations (such as calcium, magnesium, and iron) than with monovalent cations (such as sodium and potassium). - This is due to the higher charge density of divalent cations, which makes them more susceptible to binding with negatively charged groups in dietary fibers.