What is a non starch polysaccharide?

January 5, 2026 •

3 min read

Over 90% of a plant's cell wall is made up of non-starch polysaccharides (NSP), also known as dietary fiber. These complex carbohydrates play a crucial role in plant structure and are indigestible by human enzymes, offering numerous health benefits through fermentation in the gut. This article explores what non-starch polysaccharides are, how they differ from starch, their types, and their significant impact on human health.

Quick Summary

A non-starch polysaccharide (NSP) is a complex carbohydrate and a major part of dietary fiber found in plant cell walls. Unlike starch, it cannot be digested by human enzymes, but is fermented in the large intestine by gut microbiota, leading to various health benefits.

Key Points

Indigestible Carbohydrates: Non-starch polysaccharides (NSPs) are complex carbohydrates that cannot be broken down by human enzymes, forming a key component of dietary fiber.
Differing Chemical Bonds: The primary distinction from starch lies in the molecular bonds; NSPs predominantly use β-glycosidic bonds, while starch uses α-glycosidic bonds, rendering NSPs indigestible to humans.
Two Major Types: NSPs are categorized into soluble (forming gels, e.g., pectin, beta-glucans) and insoluble (adding bulk, e.g., cellulose) varieties, each with distinct physiological effects.
Fermentation in the Gut: When NSPs reach the large intestine, they are fermented by gut microbiota, producing beneficial short-chain fatty acids (SCFAs) that support colon health.
Diverse Health Benefits: These benefits include improved digestion and bowel regularity, stabilization of blood glucose levels, reduction of blood cholesterol, and support for weight management.
Rich Food Sources: Excellent dietary sources of NSP include a wide range of plant-based foods such as whole grains, legumes, fruits, vegetables, nuts, and seeds.

The Fundamental Difference Between NSP and Starch

Both non-starch polysaccharides (NSPs) and starch are complex carbohydrates, but their chemical structures and biological functions in the human body differ significantly. Starch serves as a readily available energy source, easily broken down by human digestive enzymes into simple sugars like glucose. In contrast, NSPs are largely resistant to human digestion and are fermented by beneficial bacteria in the large intestine. This resistance is due to the different types of glycosidic bonds that link their monosaccharide units. While starch is composed exclusively of α-glycosidic bonds, NSPs predominantly feature β-glycosidic bonds, which human enzymes cannot hydrolyze.

Starch vs. Non-Starch Polysaccharides


Feature	Starch	Non-Starch Polysaccharide (NSP)
Digestibility	Easily digested by human enzymes (e.g., amylase).	Largely resistant to human enzymes, acting as dietary fiber.
Monosaccharide Units	Composed entirely of glucose monomers.	Consists of a variety of monomers, such as glucose, xylose, mannose, and galactose.
Glycosidic Bonds	Predominantly linked by α-glycosidic bonds.	Mainly linked by β-glycosidic bonds.
Primary Function	Energy storage in plants and energy source for humans.	Provides structural support in plant cell walls; regulates digestion and gut health in humans.
Action in the Body	Broken down into glucose and absorbed in the small intestine.	Fermented by gut bacteria in the large intestine to produce beneficial compounds.

Classification of Non-Starch Polysaccharides

NSPs can be broadly classified based on their solubility in water, which dictates their function in the body.

Soluble Non-Starch Polysaccharides (sNSPs)

Dissolve in water, forming viscous gels in the digestive tract.
Includes beta-glucans, pectins, and gums.
Sources: Oats, barley, fruits, and legumes.
Effects: Slows down the absorption of glucose, helps regulate blood sugar, and can lower blood cholesterol by binding to bile salts.

Insoluble Non-Starch Polysaccharides (iNSPs)

Do not dissolve in water and remain largely intact as they pass through the digestive system.
Includes cellulose and some hemicelluloses.
Sources: Wheat bran, whole grains, nuts, seeds, and the skins of fruits and vegetables.
Effects: Adds bulk to stool, promoting regular bowel movements and preventing constipation.

Health Benefits of Non-Starch Polysaccharides

The indigestible nature of NSPs is what provides their health-promoting effects, primarily by influencing the gut microbiome and digestive process.

Improved Gut Health: Fermentation of NSPs by colonic bacteria produces short-chain fatty acids (SCFAs), such as butyrate, which serve as an energy source for colon cells and have anti-inflammatory effects. This process supports a healthy and diverse gut microbial community.
Blood Sugar Regulation: Soluble NSPs increase the viscosity of the intestinal contents, which slows down gastric emptying and the absorption of glucose. This helps to prevent sharp spikes in blood sugar levels after a meal.
Lowered Cholesterol: Soluble NSPs can bind to bile acids, preventing their reabsorption and promoting their excretion. The liver then pulls more cholesterol from the bloodstream to produce new bile acids, resulting in a reduction of total and LDL ("bad") cholesterol levels.
Improved Bowel Function: Insoluble NSPs increase fecal bulk and decrease transit time, aiding in the prevention of constipation and other bowel disorders like diverticulitis.
Weight Management: The bulk and gelling properties of some NSPs contribute to a feeling of fullness or satiety, which can help reduce overall food intake and assist with weight control.
Reduced Risk of Chronic Diseases: Regular consumption of NSPs, as part of a fiber-rich diet, is associated with a lower risk of cardiovascular disease, type 2 diabetes, and certain cancers, particularly colon cancer.

Common Food Sources

Incorporating a variety of foods rich in non-starch polysaccharides is essential for a balanced and healthy diet. Excellent sources include:

Whole Grains: Oats, barley, brown rice, rye, and whole wheat bread.
Legumes: Beans, chickpeas, and lentils.
Vegetables: Broccoli, carrots, and asparagus.
Fruits: Apples, pears, and berries.
Nuts and Seeds: Almonds, walnuts, and flaxseeds.

Conclusion

Non-starch polysaccharides are a diverse and crucial group of carbohydrates that form the foundation of dietary fiber. Unlike starch, they are resistant to human digestive enzymes, and this very resistance is the source of their many health benefits. By promoting a healthy gut microbiome, regulating blood sugar and cholesterol, and improving bowel function, NSPs play a vital role in disease prevention and overall wellness. A balanced diet rich in whole grains, fruits, vegetables, and legumes is the best way to ensure an adequate intake of both soluble and insoluble non-starch polysaccharides. For more detailed information on dietary fiber and its role in human health, resources like the National Institutes of Health provide further insight into the complex mechanisms of these crucial nutrients.

Frequently Asked Questions

NSPs contribute to a feeling of fullness, or satiety, which can help reduce overall food intake. Soluble NSPs, in particular, form gels that slow gastric emptying, helping you feel satisfied for longer. These effects assist in managing body weight by controlling appetite and reducing calorie consumption.

The key difference is digestibility, which stems from their chemical bonds. Starch is made of glucose units joined by α-glycosidic bonds, which are easily broken down by human digestive enzymes. NSPs are made of various sugar units and joined by β-glycosidic bonds, which human enzymes cannot digest, making NSPs a type of dietary fiber.

Yes, specifically soluble non-starch polysaccharides, like beta-glucans found in oats and barley, can help lower blood cholesterol. They achieve this by binding to bile acids in the gut and promoting their excretion, which causes the body to use more cholesterol to produce new bile acids, ultimately lowering blood cholesterol levels.

Most, but not all, dietary fiber consists of non-starch polysaccharides. The term dietary fiber also includes lignin, a non-carbohydrate component of plant cell walls. Therefore, while most dietary fiber is NSP, the two terms are not completely interchangeable.

Fermentation of NSPs by beneficial gut bacteria produces short-chain fatty acids (SCFAs) like butyrate. These SCFAs serve as a crucial energy source for the cells lining the colon, support a healthy microbial balance, and contribute to overall gut health.

Insoluble NSPs are primarily found in the structural parts of plants. Good sources include whole wheat flour, wheat bran, corn, whole grains, nuts, seeds, and the outer skins of many fruits and vegetables.

Soluble NSPs are found in the inner parts of plants and legumes. Examples include oats, barley, rye, beans, apples, carrots, and citrus fruits.