Prebiotic Type Spotlight: Different Types of Fiber

Each edition of GPA’s Prebiotic Spotlight focuses on a specific prebiotic type to raise awareness around the prebiotic itself, its sources, any notable and/or recent research, and how it is used in the marketplace. This edition takes a broader approach, focusing on different types of fiber and their impact on gut health, digestion, and overall wellness. 

Overview 

Dietary fibers play a crucial role in supporting various physiological functions. The term dietary fibers refer to a heterogenous group of highly diversified compounds that vary in terms of structure and physiochemical characteristics (Partula et al., 2020). Fibers are primarily classified into two categories: soluble fibers (e.g., pectin, gums) and insoluble fibers (e.g., cellulose, lignin), each of which has distinct health effects (Alahmari, 2024). Soluble fibers form a viscous gel in the intestinal tract and are associated with increased satiety while insoluble fibers are non-viscous, characterized by a fecal-bulking ability and speed up gastrointestinal transit time (Partula et al., 2020). Another type of fiber, fermentable fiber, which can be either soluble or insoluble, increases stool bulk indirectly through fermentation byproducts that stimulate contractile activity in the gut and increase microbial biomass (van der Schoot et al., 2022).  

Benefit Areas 

To date, several studies have described associations between dietary fiber consumption and various health benefits. Dietary fiber can modulate the gut microbiota, specifically by increasing bacteria considered beneficial (Granado-Serrano et al., 2022). Soluble fiber increases intestinal viscosity, delays nutrient absorption, and inhibits the absorption of cholesterol and bile acids, leading to various health benefits (dos Santos Fechine et al., 2021). Insoluble fiber is known to reduce gut transit time by fecal bulking and helps to keep bowel movements regular (Onali et al., 2025). Research further demonstrates the differentiated health benefits from various types of dietary fiber, including: 

• Chitin-glucan supplementation, an insoluble dietary fiber, increased bacterial taxa (Erysipelotrichaceae, Ruminococcaceae, and Eubacterium ventriosum) and improved postprandial glycemic response in adults with cardiometabolic risk (Ranaivo et al., 2022). 

• Avocado supplementation, a good source of insoluble fiber, resulted in lower fecal bile acid concentrations, increased fecal fatty acid and short chain fatty acids (SCFAs), and greater relative abundance of fiber-fermenting bacteria in healthy adults (Thompson et al., 2021).  

• Whole grain wheat products, a rich source of insoluble fiber, increased the relative abundance of several bacterial taxa from the family Ruminococcaceae and enhanced predicted fermentation pathways, compared to refined wheat products in overweight and obese adults (van Trijp et al., 2021).    

• Both viscous and particulate fibers increased colonic transit time in healthy adults (Gunn et al., 2020). 

• Wheat bran extract, a fermentable fiber, increases fecal Bifidobacterium and softens stool consistency without major effects on energy metabolism in healthy humans with a slow gastrointestinal transit (Muller et al., 2020).  

• Dietary fiber supplementation led to increased hemoglobin, serum iron, and serum ferritin compared to a control in adults with end-stage renal disease (Li et al., 2022). 

• Soluble fiber intake was associated with increased fecal SCFA content in adults with type 1 diabetes (Igudesman et al., 2023).  

• Consumption of bean hull rolls, rich in insoluble fiber, significantly increased plasma concentration of indole-3-propionic acid, a metabolite associated with lower likelihood of type 2 diabetes in healthy adults (Sayegh et al., 2023).  

• Consumption of soluble fiber-rich, fermented brewers’ spent grain resulted in significantly lower postprandial glucose levels in adults with metabolic syndrome, compared to a control group (Xu et al., 2024). 

• Supplementation with fermentable corn bran arabinoxylan enhanced satiety following a meal and decreased homeostatic model of insulin resistance (HOMA-IR) in adults with excess weight (Deehan et al., 2022). 

• Supplementation with either glucomannan, inulin, and psyllium fiber significantly promoted weight loss and improved body composition in adults with obesity, especially those with specific genetic polymorphisms (Pokushalov et al., 2024).  
   

Sources 

Dietary fibers are non-digestible carbohydrates found in plant foods such as fruits, legumes, vegetables, and whole grains. The beneficial effects of fiber vary according to the fiber types (Ma et al., 2021). Dietary fibers generally are grouped into two main categories: soluble and insoluble, which are based on the fiber’s chemical composition, with most plants containing both types in differing amounts (Zademohammadi et al., 2024). Soluble fibers, such as plant pectin and gums, dissolve in water and form a gelatinous environment in the gut, while insoluble fibers, such as plant cellulose and hemicellulose do not dissolve in water; instead, they add bulk to stools and accelerate intestinal transit time (Zademohammadi et al., 2024). Solubility is additionally correlated to fermentability, and soluble dietary fibers are fermented more quickly than insoluble dietary fibers (Ranaivo et al., 2022). In recent years, food products with enriched fiber content have gained popularity in the global marketplace (Brandl et al., 2022).  

Dose Range 

It is widely accepted that including a variety of fiber-rich foods, such as fruits and vegetables, as part of a balanced diet is vital for maintaining overall health and well-being. In the United States, dietary guidelines recommend a daily intake of 14 grams of fiber per every 1000 kcals; however, more than 90% of American women and 97% of American men do not meet these recommendations (Dietary Guidelines for Americans, 2020). Health Canada recommends Canadian women and men to consume 25 and 38 grams of fiber per day, respectively (Health Canada, 2025). Moreover, Ranaivo et al. (2022) observed that 4.5 grams of chitin-glucan for 3 weeks modulated the microbiome and improved glycemic response in adults at cardiometabolic risk, while Thompson et al. (2021) and van Trijp et al. (2021) observed a microbiota modulation from fiber-rich foods (avocados and whole grain wheat products) at doses of 75 grams to 98 grams for 12 weeks, respectively. A study by Muller et al. (2020) observed gut microbiota modulation and improved stool consistency at doses of 15 grams/day of fermentable fiber for a duration of 12 weeks in adults with slow gastrointestinal transit. Additionally, consumption of the soluble fiber-rich, fermented brewers’ spent grain resulted in significantly lower glucose levels postprandially in adults with metabolic syndrome, at a dose of around 10.7 grams/day.  

Recent Research 

Dietary fiber has been widely studied for its critical role in supporting both gut and systemic health. Currently, 309 studies listed on ClinicalTrials.gov are recruiting participants to investigate the impact of fiber supplementation on diverse health outcomes such as intestinal barrier function, inflammation, cognitive health, and satiety (ClinicalTrials.gov, 2025). Moreover, searching of “fiber” on PubMed retrieved 77 clinical trials published in 2025 so far, ranging from the effects of various types of fiber supplementation on gut permeability, microbiota, constipation, and inflammation (PubMed, 2025).  

A three-arm, randomized, double-blinded, crossover, placebo-controlled study by Nieman et al. (2025) investigated the effects of 2-week ingestion of hemp fiber versus placebo bars on gut permeability and plasma metabolite shifts during recovery from a 2.25-hour intensive cycling session. Twenty-three male and female cyclists were randomized to either consume supplement bars containing 20, 5, or 0 grams of hemp hull powder per day. Participants engaged in an intensive bout of cycling at the end of each of the three supplementation periods. Blood samples were collected before and after supplementation, as well as immediately, 1.5 hours, and 3 hours post exercise. Urine samples were collected pre-supplementation and following the bout of exercise, after ingesting a sugar solution. Significant effects of hemp fiber intake on multiple metabolic pathways were observed. Overall, hemp fiber intake during a 2-week supplementation period did not have a significant effect on post-exercise gut permeability in cyclists. However, untargeted metabolomics revealed that consuming nutrient-rich hemp fiber bars combined with 2.25 hours of exercise increased levels of beneficial metabolites, including those derived from the gut in healthy cyclists. These findings indicate that the combination of hemp hull fiber with 2.25-hour cycling, selectively influences gut permeability and has a significant impact on lipid, bile acid, and amino acid-related metabolic pathways.  

A randomized, double-blind, and placebo-controlled trial by Luk-In et al. (2025) investigated the effects of resistant starch type 3 (RS-3), a dietary fiber, in adults with self-reported chronic constipation. A total of 87 adults with chronic constipation were randomized to consume 9 grams of RS-3 or a placebo daily for 12 weeks. Participants were given medical examinations at baseline and at 6 and 12 weeks of intervention which included fasting blood glucose, anthropometry, and body composition, and the modified Constipation Scoring System (CSS) and Bristol Stool Scale (BSS) questionnaires were used to gain insight into bowel movement frequency and stool consistency. Compared to the placebo, consumption of RS-3 resulted in significant improvements in gut health by dramatically increasing levels of beneficial bacteria (Bifidobacterium, Prevotella, Akkermansia, and Megamonas) and relieving constipation. RS-3 consumption was associated with a significantly increased frequency of bowel movements, with participants reporting passing healthy stools. These findings provide insights into the therapeutic advantage of RS-3 for constipation, and its potential as an alternative strategy for management of chronic constipation.  

A secondary analysis of a randomized, double-blinded, crossover, placebo-controlled clinical trial by Romo et al. (2025) investigated the effects of fiber supplementation on the function of high-density lipoproteins, as measured by lecithin cholesterol acyltransferase (LCAT) activity, and on gut permeability, as measured by LPS- binding protein (LBP) concentrations. Twenty healthy, young adults consuming a low-fiber diet at baseline were randomized to consume a daily dose of 12 grams of prebiotic fiber or placebo daily for four weeks with four-week washout period in-between treatments. Fiber supplementation did not significantly alter LCAT activity, however in a subgroup of individuals with elevated baseline LBP concentrations, fiber supplementation significantly reduced LBP. Positive correlations were observed between microbial genes involved in LPS synthesis, while negative correlations were found with genes involved in antibiotic synthesis and LBP. Positive correlations between LBP and multiple sulfated molecules were also found. These findings highlight the potential of affordable, easy to implement fiber supplementation as an approach to mitigate gut barrier dysfunction-associated inflammation in individuals who are low-fiber consumers.   

How are fibers used in the marketplace? 

According to Future Market Insights, Inc. (2025a), the global insoluble fiber market size is estimated to reach $3.15 billion USD in 2025 and expected to grow at a compound annual growth rate (CAGR) of 9.1%, reaching an estimated $7.53 billion USD by 2035. The demand for insoluble substances is expected to increase due to factors like the growing popularity of diets for weight loss. By product type, cellulose segment dominates the insoluble fiber market at a market share of 28% and is expected to grow over the next ten years. More products are enhanced with dietary fibers to appeal to consumers who are health-conscious, with the beverage and functional food segment leading the market. In contrast, the soluble fiber market size is estimated to reach $5.8 billion USD in 2025 and expected to grow at a CAGR of 8.2% to reach $12.7 billion USD by 2035 (Future Market Insights, 2025b). Oats dominate the soluble fiber market, holding a 75% share and are widely used as the principal ingredient in a large variety of foods. Consumer awareness and healthy living movements are the driving force of the soluble fiber sector in Europe and North America. Furthermore, prebiotic fiber market size is estimated to reach $7.69 billion USD in 2025 and is expected to grow at a CAGR of 6.7% to reach $14.72 billion USD by 2035, driven by the growing need for digestive health support and microbiome-friendly formulations in everyday foods, beverages, and dietary supplements (Future Market Insights, 2025c).