What do disaccharides include? The primary types explained

January 12, 2026 •

2 min read

The human body must break down all disaccharides into simpler, single sugars (monosaccharides) before they can be absorbed and utilized for energy. This process is crucial for understanding how we derive energy from common foods like milk and table sugar.

Quick Summary

Disaccharides are carbohydrates formed from two monosaccharide units linked by a glycosidic bond. Common examples include sucrose (table sugar), lactose (milk sugar), and maltose (malt sugar). They serve as a key energy source and are broken down by specific enzymes during digestion.

Key Points

Basic Structure: Disaccharides are 'double sugars' composed of two linked monosaccharide units, such as glucose, fructose, or galactose.
Common Types: The three most well-known disaccharides are sucrose (glucose + fructose), lactose (galactose + glucose), and maltose (glucose + glucose).
Formation Process: They are created through a dehydration synthesis reaction, which removes a water molecule to form a glycosidic bond between two monosaccharides.
Digestion Mechanism: In the body, specific enzymes like sucrase, lactase, and maltase break them down into monosaccharides through a process called hydrolysis.
Nutritional Role: Disaccharides serve as a vital energy source; however, conditions like lactose intolerance highlight the necessity of proper enzymatic function for digestion.
Properties: The type of glycosidic bond determines whether a disaccharide is reducing (like lactose and maltose) or non-reducing (like sucrose).

What do disaccharides include? The composition of double sugars

Disaccharides are carbohydrates often called 'double sugars' because they are made of two linked monosaccharide units. This connection, a glycosidic bond, forms through dehydration synthesis, removing a water molecule. The specific monosaccharides and the bond type determine properties like sweetness and digestibility. The general formula for many is C12H22O11.

The most common disaccharides and their components

Several disaccharides are common in human diets and everyday foods.

Sucrose (Table Sugar)

Sucrose is common table sugar, found in sugar cane, sugar beets, and fruits.

Composition: Glucose and fructose.
Glycosidic Bond: $\alpha(1\to2)\beta$.
Properties: It is a non-reducing sugar.

Lactose (Milk Sugar)

Lactose is the main carbohydrate in mammal milk.

Composition: Galactose and glucose.
Glycosidic Bond: $\beta(1\to4)$.
Digestion: Requires the enzyme lactase; lack of it causes lactose intolerance.

Maltose (Malt Sugar)

Maltose is less common, formed during grain germination and starch breakdown.

Composition: Two glucose units.
Glycosidic Bond: $\alpha(1\to4)$.
Occurrence: Used in candy and found in beers.

Other notable disaccharides

Trehalose: Two glucose molecules with a different link, found in yeast and insects.
Cellobiose: Two glucose units with a $\beta(1\to4)$ bond, from cellulose breakdown.
Lactulose: A synthetic fructose-galactose disaccharide used as a laxative.

The process of forming and breaking down disaccharides

Disaccharides are vital for metabolism, acting as transport and energy molecules.

Formation: Dehydration Synthesis

Monosaccharides combine via dehydration synthesis, forming a glycosidic bond and releasing water. This creates compact molecules for transport and storage.

Digestion: Hydrolysis

For energy use, disaccharides are hydrolyzed back into monosaccharides by adding water. Enzymes in the small intestine, like sucrase, lactase, and maltase, facilitate this breakdown. The resulting monosaccharides are absorbed into the bloodstream. Humans cannot digest certain $\beta$-glycosidic bonds, such as those in cellulose.

Comparison of common disaccharides


Disaccharide	Monosaccharide Units	Glycosidic Bond	Common Source	Nutritional Function
Sucrose	Glucose + Fructose	$\alpha(1\to2)\beta$	Sugar cane, sugar beets, fruits	Energy source, sweetener
Lactose	Galactose + Glucose	$\beta(1\to4)$	Milk and dairy products	Energy source for infants
Maltose	Glucose + Glucose	$\alpha(1\to4)$	Germinating grains, starch digestion	Energy source

Conclusion: The fundamental role of disaccharides

Disaccharides are fundamental to nutrition and biochemistry, composed of two simple sugar units. Common examples like sucrose, lactose, and maltose illustrate how these double sugars serve as crucial energy sources. They are broken down into monosaccharides in the small intestine via enzymatic hydrolysis, providing fuel for the body. Understanding their types, sources, and digestion is key to dietary choices. For more, see the Disaccharide - Wikipedia entry.

Frequently Asked Questions

The primary function of a disaccharide is to serve as a readily available energy source for the body. During digestion, disaccharides are hydrolyzed into their component monosaccharides, which are then absorbed and used for cellular energy.

Sucrose is a non-reducing sugar because the glycosidic bond connecting its glucose and fructose units involves the anomeric carbons of both monosaccharides. This prevents a free hemiacetal unit from forming, which is necessary for a sugar to be reducing.

Both maltose and cellobiose are composed of two glucose molecules. The key difference lies in their glycosidic bond: maltose has an $\alpha(1\to4)$ linkage, while cellobiose has a $\beta(1\to4)$ linkage. The human body can digest maltose but not cellobiose.

Lactose intolerance in adults occurs because their bodies produce less of the enzyme lactase, which is necessary to break down lactose into glucose and galactose. This leads to digestive issues when consuming dairy products.

A monosaccharide is a single sugar molecule, representing the simplest form of carbohydrate (e.g., glucose). A disaccharide is a double sugar, formed by two monosaccharides joined together via a glycosidic bond (e.g., sucrose).

Trehalose, a disaccharide made of two glucose units, is found in various organisms including fungi, yeast, and insects. It is known for its high water retention properties.

No, not all disaccharides have the same nutritional value. Although they all provide energy, their component monosaccharides and how they are digested can differ. For example, lactose requires the enzyme lactase, and synthetic disaccharides like lactulose are not absorbed by the body.