Oligosaccharides: What Carbohydrate Has 3-10 Monosaccharides?

December 8, 2025 •

4 min read

Over 200 types of Human Milk Oligosaccharides (HMOs) have been identified, showcasing the biological importance of these complex sugars in infant development. This type of carbohydrate, known as an oligosaccharide, is defined by its structure containing a chain of 3 to 10 monosaccharides, or simple sugar units. Unlike simple sugars, these compounds act as crucial prebiotics that feed beneficial gut bacteria rather than being digested for energy.

Quick Summary

Oligosaccharides are carbohydrates containing 3 to 10 monosaccharide units that are largely indigestible by human enzymes. They function as prebiotics, nourishing beneficial gut bacteria and supporting digestive and immune health. Key examples include fructo-oligosaccharides and galacto-oligosaccharides, found in many plant-based foods.

Key Points

Oligosaccharides Defined: A carbohydrate composed of a chain of 3 to 10 monosaccharides, or simple sugars, linked by glycosidic bonds.
Indigestible Prebiotics: Most oligosaccharides are not digested by human enzymes in the small intestine and function as prebiotics, feeding beneficial gut bacteria.
Support Gut Health: The fermentation of oligosaccharides in the large intestine produces short-chain fatty acids (SCFAs) that nourish colon cells and support the gut barrier.
Immune System Benefits: A balanced gut microbiome, promoted by oligosaccharides, is linked to enhanced immune function and protection against pathogens.
Common Dietary Sources: Found in many plant-based foods, including chicory, onions, garlic (FOS), legumes, and human milk (GOS).
Potential for Discomfort: In sensitive individuals, fermentation can cause gas and bloating. These carbohydrates are part of the FODMAP family, which are restricted in certain diets.

Understanding the Structure of Oligosaccharides

Oligosaccharides are saccharide polymers composed of a 'few' monosaccharide units, from the Ancient Greek word oligos. These units, which can be identical or different, are linked together by glycosidic bonds. This structural characteristic places oligosaccharides between monosaccharides (single units) and polysaccharides (many units) in terms of size and complexity. The specific type of glycosidic bond and the arrangement of the monosaccharides determine the oligosaccharide's unique properties and function. For example, some bonds are digestible by human enzymes, like those in maltotriose, while others are not, allowing them to pass to the colon intact.

Digestion and Prebiotic Function

One of the most significant aspects of oligosaccharides is their resistance to digestion in the upper gastrointestinal tract. Humans lack the specific enzymes required to break down many of the glycosidic bonds present in these molecules. As a result, the majority of oligosaccharides travel undigested to the large intestine, where they are fermented by the resident gut microbiota. This fermentation process produces beneficial short-chain fatty acids (SCFAs), such as butyrate, which serve as an energy source for colon cells, support the gut barrier, and have anti-inflammatory effects.

Essentially, oligosaccharides act as prebiotics—a type of dietary fiber that selectively feeds and promotes the growth of beneficial gut bacteria, such as Bifidobacteria and Lactobacillus. By doing so, they help create a balanced gut microbiome, which is strongly linked to overall health, improved immunity, and defense against pathogens.

Types of Oligosaccharides and Dietary Sources

There are several major families of oligosaccharides, each derived from different dietary sources. The most widely studied and consumed include fructo-oligosaccharides (FOS), galacto-oligosaccharides (GOS), and human milk oligosaccharides (HMOs).

Fructo-oligosaccharides (FOS)

FOS are composed of short chains of fructose units and are common in many plants.

Sources: Onions, garlic, chicory root, asparagus, Jerusalem artichoke, and bananas are rich natural sources.
Function: They are widely used as low-calorie sweeteners and dietary supplements due to their prebiotic effects.

Galacto-oligosaccharides (GOS)

GOS are made of short chains of galactose units and are found in legumes and dairy.

Sources: Legumes like lentils, chickpeas, and beans are primary plant sources. They are also found in significant concentrations in human milk.
Function: In addition to their prebiotic role in the gut, GOS in human milk are crucial for the development of an infant's immune system and gut health.

Raffinose Family Oligosaccharides (RFOs)

RFOs are a group of oligosaccharides that includes raffinose, stachyose, and verbascose.

Sources: These are found in vegetables like broccoli, cabbage, and Brussels sprouts, as well as legumes.
Function: Like other indigestible oligosaccharides, they pass through the digestive system to be fermented in the colon, which can sometimes lead to gas and bloating.

Comparison of Common Oligosaccharides


Feature	Fructo-oligosaccharides (FOS)	Galacto-oligosaccharides (GOS)	Raffinose Family Oligosaccharides (RFOs)
Monosaccharide Units	Short chains of fructose, often with a terminal glucose.	Chains of galactose, often with a terminal glucose.	Composed of galactose, glucose, and fructose.
Polymerization (DP)	Short-chain FOS: 2-9 units. Inulin (longer-chain): 10+ units.	Typically ranges from 2 to 10 units.	Raffinose (3 units), stachyose (4 units).
Primary Sources	Chicory, garlic, onions, asparagus, bananas.	Legumes (beans, lentils), human and cow's milk.	Legumes, cabbage, broccoli, whole grains.
Digestibility	Indigestible in the small intestine, fermented in the colon.	Indigestible in the small intestine, fermented in the colon.	Indigestible in humans due to lack of the enzyme α-galactosidase.
Health Impact	Promotes growth of Bifidobacteria, aids digestion, low-calorie sweetener.	Supports infant gut health, prebiotic effects, improves mineral absorption.	Prebiotic effects, but can cause gas due to bacterial fermentation.

Impact on Health and Digestion

Beyond their foundational role as prebiotics, oligosaccharides have been associated with a range of health benefits, primarily stemming from the gut microbiome's activities. A balanced microbiota, supported by oligosaccharides, improves digestive function, enhances the immune system, and can contribute to better metabolic health by potentially influencing blood sugar levels and weight management. For instance, certain oligosaccharides can improve the absorption of minerals like calcium and magnesium, which is particularly important for bone health. Some research even suggests benefits related to reducing the risk of certain infections by acting as 'decoy receptors' that prevent pathogens from attaching to host cells.

However, it is important to note that the fermentation of oligosaccharides in the colon can produce gas, leading to digestive discomfort such as bloating and cramping in sensitive individuals, including those with Irritable Bowel Syndrome (IBS). This is why oligosaccharides are classified as FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols) and are often restricted in specific dietary plans to manage symptoms. For most healthy individuals, a gradual increase in intake allows the gut microbiome to adapt, often minimizing discomfort. Supplementing with specific digestive enzymes can also help break down these carbohydrates before they reach the colon.

Conclusion: The Importance of Oligosaccharides

The carbohydrate that consists of 3-10 monosaccharides is known as an oligosaccharide. These molecules are not merely fillers; they are complex, functionally important nutrients with significant implications for human health. By acting as prebiotics, they provide essential nourishment for beneficial gut bacteria, which in turn produce health-promoting compounds. This fundamental role in maintaining a balanced gut microbiome highlights the interconnectedness of nutrition and digestive wellness. Whether sourced naturally from a diet rich in plants and dairy or added to foods as functional ingredients, oligosaccharides play a vital part in supporting a healthy body, from immune function to metabolic health. As research continues to uncover their diverse roles, it is clear that these 'few-sugar' chains are a powerful component of a healthy diet.

Learn more about oligosaccharides, FODMAPs, and digestive health with this comprehensive guide.

Frequently Asked Questions

The primary function of oligosaccharides is to act as prebiotics, serving as food for beneficial bacteria in the large intestine. This fermentation process produces short-chain fatty acids, which provide energy for colon cells and support gut health.

Common food sources rich in oligosaccharides include onions, garlic, leeks, asparagus, bananas, wheat, and chicory root (FOS) as well as legumes like beans, lentils, and chickpeas (GOS).

Oligosaccharides are largely indigestible by human enzymes in the small intestine and, therefore, are not a direct source of energy for the body in the same way simple sugars are. However, their fermentation in the colon produces short-chain fatty acids (SCFAs), which can be absorbed and used for energy by colon cells.

The key difference lies in their size. Oligosaccharides are composed of a small number (typically 3–10) of monosaccharide units, whereas polysaccharides are much larger, containing more than 10 monosaccharide units in a long chain.

Oligosaccharides can cause bloating and gas because they are not fully absorbed in the small intestine. When they reach the large intestine, gut bacteria ferment them, producing gas as a byproduct. This can cause discomfort, especially in individuals with sensitivities like IBS.

HMOs are a unique and complex type of oligosaccharide found in human breast milk. They are distinct in structure and quantity from those found in plants and are crucial for establishing a healthy gut microbiome and developing the immune system in infants.

The 'O' in the FODMAP acronym stands for Oligosaccharides. This group of fermentable carbohydrates can cause digestive issues for sensitive individuals when consumed in large amounts.