The Scientific Meaning of Non-Starch Polysaccharides
Non-starch polysaccharides (NSP) are a category of complex carbohydrates found in plant cell walls. Unlike starches, which are easily digested into glucose by human enzymes, NSPs are resistant to this enzymatic breakdown. This resistance is due to the unique chemical structure of their glycosidic bonds, which human digestive enzymes cannot hydrolyze. The non-digestible nature of NSPs is what gives them their primary function and health benefits. Rather than being absorbed for energy, they pass largely intact through the stomach and small intestine, where they are then partially or completely fermented by beneficial bacteria in the large intestine (colon). This fermentation process produces short-chain fatty acids (SCFAs), which are a vital energy source for the cells lining the colon and have numerous systemic health benefits.
The term "dietary fiber" is the more commonly used and practical name for NSP in a nutritional context. However, it is important to note that the chemical definition of dietary fiber can also include other components, such as lignin and some types of resistant starch, which are not technically polysaccharides. For most dietary purposes, referring to NSP as dietary fiber is accurate and sufficient.
Types of Non-Starch Polysaccharides
Non-starch polysaccharides are a diverse group of compounds with varying properties, which influence their effects on the body. They are broadly categorized into two main types based on their solubility in water.
Soluble Non-Starch Polysaccharides (sNSP)
- Dissolve in water to form a gel-like substance.
- Slow down the movement of food through the digestive tract, which can help control blood sugar and cholesterol levels.
- Are highly fermentable by gut bacteria, contributing to the production of beneficial SCFAs.
- Common examples include pectins, gums, and β-glucans.
Insoluble Non-Starch Polysaccharides (iNSP)
- Do not dissolve in water and pass through the digestive system largely unchanged.
- Add bulk to the stool and help promote regular bowel movements, preventing constipation.
- Have a laxative effect due to their bulking properties and promotion of a faster transit time.
- Examples include cellulose, hemicellulose, and lignin (though lignin is not a polysaccharide).
Health Benefits of a High-NSP Diet
Incorporating a diet rich in non-starch polysaccharides is associated with numerous health advantages. These benefits stem from the bulk-forming properties of insoluble fiber and the fermentable nature of soluble fiber.
Digestive Regularity: Insoluble NSPs, such as those found in wheat bran and whole grains, add bulk to stool, which helps it pass through the colon more quickly and easily. This is effective for preventing and treating constipation and can help reduce the risk of diverticular disease.
Cardiovascular Health: Soluble NSPs, particularly β-glucans from oats and barley, are known to have a cholesterol-lowering effect. They can bind to bile acids in the digestive tract, preventing their reabsorption and forcing the liver to use more cholesterol to produce new bile, thereby lowering blood cholesterol levels.
Blood Sugar Management: Soluble NSPs slow down the absorption of sugar, which helps to prevent sharp spikes in blood glucose levels after a meal. This is particularly beneficial for individuals with type 2 diabetes or those at risk of developing the condition.
Weight Management: High-fiber foods are generally more filling and can help promote a feeling of fullness or satiety. This can lead to a reduction in overall calorie intake, aiding in weight control and management.
Gut Microbiome Support: The fermentation of NSPs in the colon serves as a prebiotic effect, feeding the beneficial gut bacteria. This promotes a healthy and diverse microbiome, which is linked to a better immune response and overall gastrointestinal function.
Comparison: Non-Starch Polysaccharides vs. Resistant Starch
While both NSP and resistant starch (RS) are considered components of dietary fiber and are resistant to digestion in the small intestine, they have distinct chemical structures and properties. The key difference lies in their source and composition. NSP consists of a variety of non-alpha-glucan polysaccharides like cellulose and pectin, which are structural components of plant cell walls. Resistant starch, however, is a fraction of starch itself that escapes digestion and is fermented in the large bowel.
| Feature | Non-Starch Polysaccharides (NSP) | Resistant Starch (RS) |
|---|---|---|
| Chemical Composition | A diverse group of non-alpha-glucan polysaccharides (e.g., cellulose, pectin, β-glucans). | A fraction of starch (an alpha-glucan) that resists digestion. |
| Natural Source | Abundant in plant cell walls and tissues. | Found in whole grains, legumes, and uncooked/re-cooked starches. |
| Primary Function | Structural component of plants. | Energy storage in plants. |
| Mechanism of Resistance | Unique beta-glycosidic bonds are not hydrolyzed by human enzymes. | Physical or chemical properties prevent digestive enzyme access. |
| Effects on Digestion | Both soluble and insoluble types exist, affecting viscosity, transit time, and bulk. | Can increase fecal bulk and is highly fermentable. |
Conclusion: The Importance of Dietary Fiber (NSP)
Non-starch polysaccharides, better known as dietary fiber, are far from being just "roughage." They are a complex and varied group of carbohydrates that play a critical and multifaceted role in human health. From promoting digestive regularity and lowering cholesterol to supporting a healthy gut microbiome and aiding in blood sugar control, their benefits are numerous. A balanced diet that incorporates both soluble and insoluble NSPs from a variety of plant sources, such as whole grains, fruits, vegetables, and legumes, is key to reaping these advantages. Understanding NSP as a central component of a healthy diet emphasizes the value of minimally processed, plant-rich foods. For further reading, an academic overview of the dietary roles of non-starch polysaccharides can be found on this journal site.
Dietary Roles of Non-Starch Polysachharides in Human Nutrition
