International Journal of Molecular Medical Science, 2025, Vol.15, No.2, 98-106 http://medscipublisher.com/index.php/ijmms 100 3 Types and Mechanisms of Action of Dietary Fiber 3.1 Characteristics and differences of soluble and insoluble dietary fiber Soluble and insoluble fibers have obvious differences in characteristics and functions. Soluble fibers (such as inulin) can dissolve in water to form gel-like substances, which are easily decomposed by the intestinal flora, generating short-chain fatty acids and helping to control blood sugar (Raninen et al., 2011; Dayib et al., 2020). Insoluble fibers (such as those in whole grains) are insoluble in water and difficult to break down. They mainly help increase the volume of feces and maintain normal intestinal defecation (Stephen and Cummings, 1980; Weickert and Pfeiffer, 2018). The functions of the two types of fibers are different. Soluble fiber can delay gastric emptying and make people feel full earlier, thereby helping to control weight (Ar, 1987;) Papathanasopoulos and Camilleri, 2010. Insoluble fiber can accelerate the speed at which food passes through the intestines and prevent constipation (Stephen and Cummings, 1980; Roehrig, 1988). Understanding these differences is important for formulating a reasonable diet plan. 3.2 Regulatory effects of different dietary fibers on intestinal flora: prebiotic effect Dietary fiber can produce beneficial effects by altering the microbiota. Soluble fibers (such as inulin) are particularly suitable for promoting the growth of beneficial bacteria such as Bifidobacterium and enhancing intestinal health (Raninen et al., 2011; Dayib et al., 2020). After being decomposed by the microbiota, these fibers produce short-chain fatty acids, which can both nourish intestinal cells and combat inflammation (Roehrig, 1988; Papathanasopoulos and Camilleri, 2010). Although insoluble fibers have a relatively weak effect, they can still help diversify the flora. They provide growth conditions for some bacteria and maintain the balance of the microbiota (Stephen and Cummings, 1980; Weickert and Pfeiffer, 2018). The complex relationship between fiber and the microbiota indicates that a mixed intake of the two types of fiber is most beneficial to the intestines. 3.3 The mechanism by which dietary fiber promotes intestinal health Dietary fiber protects the intestines in many ways. Soluble fiber increases the viscosity of food, slows down the digestion rate, and helps with nutrient absorption and blood sugar control (Ar, 1987; Grundy et al., 2016). This characteristic can also assist in regulating cholesterol levels (Lattimer and Haub, 2010; Dayib et al., 2020). Insoluble fiber prevents constipation by increasing fecal volume and accelerating intestinal motility (Stephen and Cummings, 1980; Roehrig, 1988). The two types of fibers can also stimulate the secretion of mucus in the intestinal tract, enhance the intestinal protective layer, and reduce the risk of disease (Papathanasopoulos and Camilleri, 2010; Cui et al., 2019). These mechanisms jointly maintain intestinal health. 4 The composition and Proportion of Compound Dietary Fiber Preparations 4.1 Common ingredients and sources of compound dietary fiber preparations Compound dietary fiber preparations usually contain a variety of fibers, such as cellulose, pectin and hemicellulose. These fibers come from fruits, vegetables and grains respectively. Cellulose exists in the cell walls of plants and is the main dietary fiber in vegetables such as celery and kale (Zhang et al., 2023). Pectin is mostly derived from apples and citrus fruits and is a key component in the formation of jam and jelly gels (Zhang et al., 2023). The abundant hemicellulose in whole grains and legumes supplements the functions of other fibers by providing different structures (Zhang et al., 2023; Wu, 2024). It is important to add these fibers to dietary preparations because each of them is beneficial to intestinal health. Cellulose is an insoluble fiber that can increase the volume of feces and promote defecation (Zhai et al., 2018). Pectin is a soluble fiber that helps lower cholesterol and stabilize blood sugar (So et al., 2018). Hemicellulose is both soluble and insoluble, which can promote the growth of probiotics and improve nutrient absorption (Li et al., 2023). Combining these fibers together can provide a comprehensive fiber supplementation solution.
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