oligosaccharide

oligosaccharide: see carbohydrate.

Any carbohydrate with a few (between 3 and about 6 to 10) units of simple sugars (monosaccharides). A wide variety of oligosaccharides are made by partially breaking down polysaccharides. Most of the few naturally occurring oligosaccharides are found in plants; those in animals tend to be combined in glycoproteins.

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An oligosaccharide is a saccharide polymer containing a small number (typically three to ten) of component sugars, also known as simple sugars. The name derived from the Greek oligos, meaning "a few".

They are generally found either O- or N-linked to compatible amino acid side chains in proteins or to lipid moieties (see glycans).

Examples

Fructo-oligosaccharides (FOS), which are found in many vegetables, consist of short chains of fructose molecules. Inulin has a much higher degree of polymerization than FOS and is a polysaccharide. Galactooligosaccharides (GOS), which also occur naturally, consist of short chains of galactose molecules. These compounds can be only partially digested by humans.

Oligosaccharides are often found as a component of glycoproteins or glycolipids and as such are often used as chemical markers, often for cell recognition. An example is ABO blood type specificity. A and B blood types have two different oligosaccharide glycolipids embedded in the cell membranes of the red blood cells, AB-type blood has both, while O blood type has neither.

Mannan-oligosaccharides (MOS) are widely used in animal feed to encourage gastrointestinal health and performance. They are normally obtained from the yeast cell walls of Saccharomyces cerevisiae. Some brand names are: Bio-Mos, SAF-Mannan, Y-MOS and Celmanax.

Therapeutic effects

When oligosaccharides are consumed, the undigested portion serves as food for the intestinal microflora. Depending on the type of oligosaccharide, different bacterial groups are stimulated or suppressed.

Clinical studies have shown that administering FOS, GOS, or inulin can increase the number of these friendly bacteria in the colon while simultaneously reducing the population of harmful bacteria.

Other benefits noted with FOS, GOS, or inulin supplementation include increased production of beneficial short-chain fatty acids such as butyrate, increased absorption of calcium and magnesium, and improved elimination of toxic compounds.

Because FOS, GOS, and inulin improve colon function and may influence the bacterial composition, one might expect these compounds would help relieve the symptoms of irritable bowel syndrome. However, a double-blind trial found no clear benefit with FOS supplementation (2 grams three times daily) in patients with this condition.

Experimental studies with FOS in animals suggest a possible benefit in lowering blood sugar levels in people with diabetes and in reducing elevated blood cholesterol and triglyceride levels.

In a double-blind trial of middle-aged men and women with elevated cholesterol and triglyceride levels, supplementation with inulin (10 grams per day for eight weeks) significantly reduced insulin concentrations, suggesting an improvement in blood-glucose control, and significantly lowered triglyceride levels.

In a preliminary trial, administration of FOS (8 grams per day for two weeks) significantly lowered fasting blood-sugar levels and serum total-cholesterol levels in patients with type 2 (non-insulin-dependent) diabetes.

However, in another trial, people with type 2 diabetes supplementing with FOS (15 grams per day) for 20 days found no effect on blood-glucose or lipid levels. Because of these conflicting results, more research is needed to determine the effect of FOS and inulin on diabetes and lipid levels.

Several double-blind trials have looked at the ability of FOS or inulin to lower blood cholesterol and triglyceride levels. These trials have shown that in people with elevated total cholesterol or triglyceride levels, including people with type 2 (adult onset) diabetes, FOS or inulin (in amounts ranging from 8 to 20 grams daily) produced significant reductions in triglyceride levels. However, the effect on cholesterol levels was inconsistent. In people with normal or low cholesterol or triglyceride levels, FOS or inulin produced little effect.

Sources

FOS and inulin are found naturally in Jerusalem artichoke, burdock, chicory, leeks, onions, and asparagus. FOS products derived from chicory root contain significant quantities of inulin, a fiber widely distributed in fruits, vegetables and plants. Inulin is a significant part of the daily diet of most of the world’s population. FOS can also be synthesized by enzymes of the fungus Aspergillus niger acting on sucrose. GOS is naturally found in soybeans and can be synthesized from lactose (milk sugar). FOS, GOS, and inulin are available as nutritional supplements in capsules, tablets, and as a powder.

Not all natural oligosaccharides occur as components of glycoproteins or glycolipids. Some, such as the raffinose series, occur as storage or transport carbohydrates in plants. Others, such as maltodextrins or cellodextrins, result from the microbial breakdown of larger polysaccharides such as starch or cellulose.

References