Dietary fiber plays a crucial role in the health of your clients, influencing digestive function, metabolism and weight, and cardiovascular health. Fiber consists of plant-based carbohydrates that resist digestion in the small intestine and are either partially or fully fermented in the large intestine.¹ Fiber is categorized into two types based on solubility in water: soluble and insoluble fiber.¹ Both types contribute to chronic disease prevention, making fiber-rich foods an essential part of a healthy diet.

Most Americans fall short of the recommended dietary fiber intake due to low intakes of fiber-rich foods like fruits, vegetables, and whole grains. Over 90% of women and 97% of men do not meet daily fiber recommendations, with recent studies showing that adult females in the US consume, on average 15g/day and adult males consume 18g/day.^2,3 The Institute of Medicine recommends 14g of fiber per 1000kcals consumed; the daily value (DV) on nutrition labels is 28g on a 2000kcal diet.^3,4 Helping clients shift dietary patterns to include more whole, unprocessed plant foods can help bridge this fiber gap and improve health outcomes. 

Understanding Fiber: Soluble vs. Insoluble

Soluble fiber, found in oats, legumes, and fruits like apples, oranges, and pears, includes compounds like inulin, pectins, and β-glucans.¹ It dissolves in water to form a gel-like substance, helping to regulate blood sugar levels, promote satiety, and help lower blood cholesterol levels.¹ Soluble dietary fiber intake can help reduce gastrointestinal diseases, including irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), diverticular disease, constipation, fecal incontinence, and colorectal cancer because of the positive effects it has on the gut microbiome and the metabolites (including short-chain fatty acids (SCFAs)) made there.⁵

Insoluble fiber does not dissolve in water, so it promotes bulk and movement through the digestive tract, promoting bowel regularity and reducing constipation.¹ It consists of cellulose, lignin, and some hemicelluloses.¹ Insoluble fiber is found in whole grains/wheat bran, nuts, seeds such as chia, fruit skin, and certain vegetables like spinach and broccoli. Though insoluble dietary fiber is not utilized by the gut bacteria the way soluble fiber is (to create SCFAs, etc), intake is still essential for regulating a healthy bowel movement pattern.⁵ Recent studies have also shown bioactive compounds like phenolic acids and flavonoids may also contribute health benefits through free radical management and reactive oxygen species scavenging, possibly exhibiting anti-inflammatory and other health effects.⁴

Soluble and insoluble fiber amounts aren’t specifically listed on labels, and many foods are combinations of both fiber types. Some preliminary studies have shown potential benefits regarding a soluble-to-insoluble ratio of 3:1, which may increase satiety and lower hormones such as cholecystokinin (CCK) and insulin.⁶ Healthcare professionals can help their clients work towards meeting their fiber goals and may recommend more soluble or insoluble sources based on individual health goals or gastrointestinal symptoms. 

 Dietary Fiber and Health

Metabolic Health and Weight Management

Dietary fiber supports weight management and metabolic health, including blood sugar management, by promoting satiety through mechanical and hormonal mechanisms.⁷  Fiber intake triggers gastric distension, slows gastric emptying, and increases the delivery of unabsorbed nutrients to the ileum in the small intestine, all of which contribute to prolonged fullness. Fiber fermentation in the gut produces SCFAs that stimulate enteroendocrine cells to release appetite-regulating hormones like glucagon-like peptide-1 (GLP-1) and peptide YY (PYY), which also may help reduce food intake and improve glycemic response.^7,8 For example, a recent study called the Full Plate Living program, a 16-week plant-predominant, fiber-rich eating initiative, was implemented across 72 employers for two years. Of the 4,477 participants, 62.5% achieved weight loss. A retrospective analysis assessed dietary fiber intake and weight outcomes, comparing changes in servings of fiber-rich foods—fruits, vegetables, whole grains, beans, and nuts. The weight loss group saw an average weight reduction of 3.28kg and had significantly higher intakes of fruits, vegetables, and beans, with a statistically significant increase in whole grain consumption (p < 0.05).⁹ A meta-analysis of 22 randomized controlled trials (N=911) found that consuming dietary fiber significantly reduced HbA1c, fasting blood glucose, fasting insulin, and insulin resistance (HOMA-IR) at a median intake of 10g/day over eight weeks.¹⁰ Ten grams of fiber can be found in ½ cup unsweetened bran cereal, an artichoke, ½ cup navy beans, or about a cup of guava fruit.¹¹

Cardiovascular Benefits

Fiber has a direct link to better cardiovascular outcomes. It has been shown to play a role in lowering LDL (“bad”) cholesterol, regulating blood pressure, and possibly helping reduce inflammation.^1,3,12 A large study (N=12,131 participants without hypertension at baseline) using data from the China Health and Nutrition Survey found that during the study, with a median follow-up of 6.1 years, 4,252 participants were diagnosed with hypertension and a higher insoluble fiber variety score was significantly associated with a lower risk of new-onset hypertension (per score increment, HR = 0.50; 95% CI: 0.45–0.55).¹²

A meta-analysis of 181 randomized controlled trials (N=14,505 participants) assessed the impact of soluble fiber supplementation on blood lipids in adults and found significant reductions in LDL cholesterol (−8.28 mg/dL), total cholesterol (−10.82 mg/dL), triglycerides (−5.55 mg/dL), and apolipoprotein B (−44.99 mg/L) in intervention compared to control groups.¹³ A dose-response effect showed that each 5 g/day increase in soluble fiber intake led to further reductions in total cholesterol (−6.11 mg/dL) and LDL cholesterol (−5.57 mg/dL).¹³ Five grams of fiber (both soluble and insoluble) can be found in 2 teaspoons of chia seeds, ½ cup of white beans or black-eyed peas, an apple, or 1 cup of raspberries, which are easy suggestions healthcare providers can make if their clients have goals to manage their blood lipids.¹¹

Gut and Digestive Health

Dietary fiber plays a role in gut health by ‘feeding’ the gut microbiome, alleviating constipation, and potentially reducing IBS symptoms.^14,15 Certain fibers – especially soluble fibers and resistant starches – act as a ‘prebiotic’ to fuel beneficial gut bacteria.^14,15 As these fibers escape digestion in the upper gastrointestinal tract, they undergo fermentation by gut microbes in the colon, and this process produces SCFAs (butyrate, acetate, and propionate), which provide energy for colon cells and contribute to systemic metabolic and cardiovascular benefits.¹⁴ Microbial interactions with dietary fiber enhance gut barrier function, reduce inflammation, and have been linked to lower risks of IBD, colorectal cancer, and metabolic disorders.^5,14,15

Takeaways for Healthcare Providers

Healthcare providers should educate patients on how much fiber they need to intake for their health goals and assess patients’ diets to assess gaps in intake vs recommendations, knowing that most Americans do not meet their needs, and how that can negatively impact health goals. 

Individual health conditions like IBS, IBD, or diverticulosis (among others) may need adjustments in the type or amount of fiber patients consume based on their symptoms and medical advice from their team.
The Dietary Guidelines for Americans have a great resource for food sources of dietary fiber, including printable versions of ready-to-use handouts. Visit the DGA fiber page for more information, including portions, calories, and fiber grams for different food groups.¹¹ 

References:

1. He Y, Wang B, Wen L, et al. Effects of dietary fiber on human health. Food Science and Human Wellness. 2022 Jan 1;11(1):1-0.
2. U.S. Department of Agriculture, Agricultural Research Service. Nutrient Intakes from Food and Beverages: Mean Amounts Consumed per Individual, by Gender and Age. 2022. Available online: https://www.ars.usda.gov/northeast-area/beltsvillemd-bhnrc/beltsville-human-nutrition-research-center/food-surveys-research-group/docs/wweia-data-tables
3. U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020-2025. 9th Edition. December 2020. Available at DietaryGuidelines.gov.
4. Timm M, Offringa LC, Van Klinken BJ, Slavin J. Beyond insoluble dietary fiber: bioactive compounds in plant foods. Nutrients. 2023;15(19):4138.
5. Guan ZW, Yu EZ, Feng Q. Soluble dietary fiber, one of the most important nutrients for the gut microbiota. Molecules. 2021;26(22):6802.
6. Burton-Freeman B, Liyanage D, Rahman S, Edirisinghe I. Ratios of soluble and insoluble dietary fibers on satiety and energy intake in overweight pre- and postmenopausal women. Nutr Healthy Aging. 2017;4(2):157-168.
7. Akhlaghi M. The role of dietary fibers in regulating appetite, an overview of mechanisms and weight consequences. Critical Reviews in Food Science and Nutrition. 2024;64(10):3139-50.
8. Giuntini EB, Sardá FA, de Menezes EW. The effects of soluble dietary fibers on glycemic response: an overview and futures perspectives. Foods. 2022;11(23):3934.
9. Kelly RK, Calhoun J, Hanus A, Payne-Foster P, Stout R, Sherman BW. Increased dietary fiber is associated with weight loss among Full Plate Living program participants. Frontiers in Nutrition. 2023;10:1110748.
10. Mao T, Huang F, Zhu X, Wei D, Chen L. Effects of dietary fiber on glycemic control and insulin sensitivity in patients with type 2 diabetes: A systematic review and meta-analysis. Journal of Functional Foods. 2021;82:104500.
11. U.S. Department of Agriculture, Agricultural Research Service. Food Sources of Dietary Fiber. FoodData Central. 2019. https://www.dietaryguidelines.gov/resources/2020-2025-dietary-guidelines-online-materials/food-sources-select-nutrients/food-sources-fiber
12. Ye Z, Wu Q, Yang S, et al. Variety and quantity of dietary insoluble fiber intake from different sources and risk of new-onset hypertension. BMC medicine. 2023;21(1):61.
13. Ghavami A, Ziaei R, Talebi S, et al. Soluble fiber supplementation and serum lipid profile: a systematic review and dose-response meta-analysis of randomized controlled trials. Advances in Nutrition. 2023;14(3):465-74.
14. Fu J, Zheng Y, Gao Y, Xu W. Dietary fiber intake and gut microbiota in human health. Microorganisms. 2022;10(12):2507.
15. Lai H, Li Y, He Y, et al. Effects of dietary fibers or probiotics on functional constipation symptoms and roles of gut microbiota: a double-blinded randomized placebo trial. Gut Microbes. 2023;15(1):2197837.