Non-starch polysaccharides (NSPs) is a category of chemicals found naturally in plants.
Collectively non-starch polysaccharides are also known as:
- dietary fibre (British English spelling)
- dietary fiber (American English spelling), and
- roughage (older term in wide colloquial use).
In terms of both chemistry and diet and nutrition, non-starch polysaccharides are a type of carbohydrate.
When to use "non-starch polysaccharides" and when to use "dietary fibre" (or equivalent):
As these refer to the same chemicals some textbooks use them inter-changeably.
In general, 'dietary fibre' is more commonly used when describing and discussing NSPs in the diet, e.g. their functions and benefits and how they are processed by the human digestive system. 'Non-starch polysaccharides' is used when describing and explaining the chemistry, and therefore also the chemical reactions of NSPs. These are closely related because the digestive process includes chemical digestion e.g. due to the actions of acids, enzymes and bile.
- The page about dietary fibre mentions types of dietary fibre, the functions and benefits of dietary fibre and sources of dietary fibre with examples of high fibre foods and low fibre foods.
- This page about non-starch polysaccharides explains the general chemical structure of NSPs as compared with e.g. monosaccharides and disaccharides. It also lists examples of specific NSPs.
Polysaccharides compared with other carbohydrates:
As explained on the page about types of sugar (monosaccharides and disaccharides), there are 4 general categories of carbohydrates which can be listed in increasing size and complexity as:
Simple 'unit' sugar molecules.
Consist of molecules whose form is that of two monosaccharide molecules joined together.
Consist of molecules whose form is that of 3-10 monosaccharide molecules joined together.
Consist of molecules whose form is that of many monosaccharide molecules joined together.
The table above helps to explain the polysaccharide part of the expression non-starch polysaccharides.
Definition of polysaccharide:
Polysaccharides are carbohydrates (i.e. organic chemicals that consist mainly of the elements carbon, hydrogen and oxygen) whose molecules take the form of long chains of monosaccharides (i.e. simple sugars) all joined together.
The general properties of polysaccharides include insolubility in cold water, no taste, and being indigestible to humans. Polysaccharides have an important role in the human digestive system, as described on the page about dietary fibre.
Main types of polysaccharides:
There are many types of polysaccharides found in plant materials commonly included in human diets.
In terms of their chemical composition and properties, non-starch polysaccharides are:
compounds that can be classified within the categories of the above table except for (i.e. excluding) starches.
Starch is the most common carbohydrate in the human diet. It is one type of polysaccharide. There are many different starches. Their sizes and shapes are characteristic of the plant that produced them, e.g. potatoes, bananas, beans (e.g. lentils, peas and chickpeas), barley, breadfruit, oats, oca, chestnuts, water chestnuts, wheat, yams, corn (maize) and rice. In all cases pure starch is a white, tasteless and odourless powder that is insoluble in cold water or alcohol. Starch is not readily digested by humans but it is more easily digested after it has been cooked in the presence of water e.g. in bread, pancakes, noodles, pasta and porridge.
Glycogen has a similar composition to that of starch. An important difference is that it is made (from glucose) by animals rather than by plants. Although small amounts of glycogen are stored in the body as an energy reserve it is insignificant in terms of humans dietary intake because glycogen stored in animal tissue breaks back down to glucose after an animal's physical death.
Non-starch polysaccharides therefore include cellulose (which forms the bulky structure of many plants) and pectins (which come from e.g. the stones of many fruits).
Examples of non-starch polysaccharides:
This list of compounds classed as non-starch polysaccarides (NSP)s is not complete but includes examples of common NSPs.
and some other carbohydrates with β-glycosidic linkages.
Some sources also include certain oligosaccharides as 'types of non-starch polysaccharides'. That is not unreasonable because oligosaccharides consist of molecules whose structure is more than two monosaccharide molecules joined together. However, oligosaccharides are increasingly classified separately from polysaccharides so their inclusion in lists of 'examples of NSPs' might cause confusion.
See also dietary fibre, carbohydrates, fatty acids, fats, proteins and water in the diet.