What Polysaccharide Is Used as Dietary Fiber in the Human Body?

December 22, 2025 •

3 min read

Dietary fiber is a component of plant-based foods that the human body cannot digest or absorb, a fact that is central to its health benefits. Many types of complex carbohydrates, or polysaccharides, serve this role, but understanding which polysaccharide is used as dietary fiber is key to appreciating its function.

Quick Summary

Several polysaccharides function as dietary fiber in humans, with cellulose, pectin, and beta-glucans being major examples. These compounds pass undigested through the digestive tract, playing vital roles in promoting gut health and regulating metabolic processes.

Key Points

Cellulose is the primary insoluble fiber: As the main component of plant cell walls, cellulose passes undigested through the body, adding bulk and aiding bowel regularity.
Pectin acts as a soluble, gel-forming fiber: This polysaccharide, found in fruits, slows digestion and helps lower blood cholesterol and glucose levels.
Beta-glucans are powerful soluble fibers: Sourced from oats and barley, beta-glucans are highly effective at lowering blood cholesterol and regulating blood sugar due to their viscosity-generating properties.
Inulin is a key prebiotic fiber: Found in foods like chicory root and onions, inulin nourishes beneficial gut bacteria and promotes a healthy microbiome.
A mix of fiber sources is best: Consuming a variety of whole plant foods, rich in different types of polysaccharides, ensures you get both soluble and insoluble fiber for comprehensive health benefits.
Fiber fermentation produces beneficial compounds: In the large intestine, gut bacteria ferment soluble fibers like pectin and inulin into short-chain fatty acids (SCFAs), which support colon health.
Processing can affect fiber potency: The health effects of fiber depend not only on the amount but also on its physical form and molecular weight, which can be altered by cooking and processing.

Introduction to Polysaccharides and Dietary Fiber

Polysaccharides are complex carbohydrates made of sugar units. While some are digested for energy, others resist digestion by human enzymes and function as dietary fiber. The inability to break certain chemical bonds in these plant polysaccharides is why they pass through the digestive system undigested, providing various health benefits.

Dietary fiber falls into two categories: soluble and insoluble. Soluble fibers dissolve in water to form a gel, helping manage blood sugar and cholesterol, while insoluble fibers add bulk to stool and aid passage through the gut. Most plant foods contain a mix of both types.

Key Polysaccharides Acting as Dietary Fiber

Cellulose

Cellulose is a primary insoluble fiber and a major part of plant cell walls. Humans cannot digest it due to lacking the necessary enzymes.

Found in: Whole grains, wheat bran, legumes, nuts, and fruit and vegetable skins.
Function: Adds bulk to stool, promoting regular bowel movements.

Pectin

Pectin is a soluble fiber found in plant cell walls, particularly in fruits. It forms a gel in water.

Found in: Fruits (especially peels), vegetables, and legumes.
Function: Slows digestion, helps regulate blood sugar and cholesterol, and is fermented by gut bacteria.

Beta-Glucans

These soluble fibers are known for their effects on cholesterol and blood sugar. They create viscosity in the gut.

Found in: Oats, barley, rye, and some fungi.
Function: Slows absorption of glucose and cholesterol and is fermentable by gut bacteria.

Inulin

Inulin is a soluble, fermentable fiber (a fructan) that acts as a prebiotic.

Found in: Chicory root, onions, garlic, and Jerusalem artichokes.
Function: Nourishes beneficial gut bacteria, leading to the production of SCFAs that support colon health.

Hemicellulose

Found with cellulose in plant cell walls, hemicellulose can be either soluble or insoluble.

Found in: Cereal grains.
Function: Contributes to bulk and supports bowel regularity.

Comparison of Key Dietary Fiber Polysaccharides


Polysaccharide	Solubility	Primary Function	Food Sources	Notes
Cellulose	Insoluble	Adds bulk to stool, aids regularity	Wheat bran, nuts, whole grains, vegetable skins	The most abundant organic polymer on Earth.
Pectin	Soluble	Slows digestion, lowers cholesterol and blood sugar	Apples, berries, citrus fruits, carrots	Forms a gel-like substance in the digestive tract.
Beta-Glucans	Soluble	Lowers cholesterol, regulates blood sugar	Oats, barley, mushrooms, yeast	High viscosity is key to its health effects.
Inulin	Soluble, fermentable	Prebiotic, feeds beneficial gut bacteria	Chicory root, onions, garlic, asparagus	Classified as a fructan, made of fructose units.
Hemicellulose	Both soluble and insoluble	Aids regularity, bulking agent	Cereal grains	A complex and varied group of polysaccharides.

The Health Benefits of Dietary Fiber Polysaccharides

Eating a diverse range of fiber-rich plant foods provides numerous health benefits.

Digestive Health

Both soluble and insoluble fibers are vital for digestive health. Insoluble fibers like cellulose increase stool bulk, preventing constipation, while soluble fibers such as pectin can help solidify loose stools. Fermentable fibers also nourish beneficial gut bacteria.

Cholesterol and Blood Sugar Management

Soluble polysaccharides like beta-glucans and pectin form a gel that traps cholesterol and bile acids, reducing their absorption and lowering LDL cholesterol. This gel also slows sugar absorption, helping regulate blood sugar levels, especially beneficial for those managing or at risk of type 2 diabetes.

Weight Management

Fiber-rich foods promote feelings of fullness (satiety), which can help reduce overall calorie intake and support weight management.

Optimizing Your Fiber Intake

Consuming a variety of whole plant foods is the best way to get a mix of different beneficial polysaccharides. Aim for the recommended daily intake of 25-30 grams for adults.

Choose whole grains: Incorporate whole-wheat products, oats, and barley.
Eat fruits and vegetables with skin: Many fibers, including cellulose, are in the skins.
Include legumes: Beans, lentils, and peas are good sources of various fibers.
Read ingredient labels: Be aware that isolated fibers in processed foods may not offer the same benefits as whole-food fiber.

Conclusion

Key polysaccharides functioning as dietary fiber include cellulose, pectin, beta-glucans, and inulin. These indigestible complex carbohydrates offer significant health advantages, from improving digestion and regularity to managing cholesterol and blood sugar. A varied diet featuring whole grains, fruits, vegetables, and legumes ensures a good intake of these essential polysaccharides, contributing to overall health and well-being. Understanding these fibers allows for better dietary choices to optimize nutritional intake. For further nutritional guidance, resources like the Harvard T.H. Chan School of Public Health offer valuable information on fiber and its benefits.

Resources

Harvard T.H. Chan School of Public Health: The Nutrition Source: Fiber

Frequently Asked Questions

The primary function of dietary fiber is to promote digestive health. As it is not digested, it adds bulk to stool (insoluble fiber) or forms a gel that regulates nutrient absorption (soluble fiber), aiding in bowel regularity, managing blood sugar, and lowering cholesterol.

Most dietary fiber consists of polysaccharides, like cellulose, pectin, and beta-glucans. However, some non-carbohydrate components, such as lignin, are also classified as dietary fiber because they are resistant to human digestion.

Soluble fiber dissolves in water, forming a gel-like substance that slows digestion. Examples include pectin and beta-glucans. Insoluble fiber does not dissolve in water; it adds bulk to the stool and accelerates the passage of food through the digestive tract. Cellulose is a key example of insoluble fiber.

Beta-glucans are soluble fibers, typically from oats and barley, that form a viscous gel in the digestive tract. This gel binds to bile acids, which are made from cholesterol, and prevents their reabsorption. This process forces the body to use more cholesterol to produce new bile acids, resulting in lower blood cholesterol levels.

Humans cannot digest cellulose because they lack the specific enzymes, particularly cellulase, required to break down the beta-1,4-glycosidic bonds that link its glucose units together. This allows cellulose to pass through the digestive system as indigestible fiber.

Good sources of soluble fiber include oats, barley, nuts, seeds, beans, lentils, peas, and many fruits and vegetables. Pectin found in apples and citrus fruits, and beta-glucans in oats and barley, are prime examples.

Prebiotics are non-digestible food components, often fermentable polysaccharides like inulin, that selectively stimulate the growth and activity of beneficial bacteria in the gut. These bacteria then produce beneficial compounds like short-chain fatty acids (SCFAs).