What are carbs with two sugars called? Understanding disaccharides

November 8, 2025 •

3 min read

According to the U.S. National Library of Medicine, all carbohydrates, including those with two sugar units, are essential nutrients that your body converts into glucose for energy. Carbs with two sugars are called disaccharides, and they are a vital component of the food we consume daily, from table sugar to milk.

Quick Summary

This article defines what are carbs with two sugars called, details their formation through glycosidic bonds, explores common types such as sucrose, lactose, and maltose, and explains how the human body processes them for energy.

Key Points

Definition: Carbs with two sugars are called disaccharides, composed of two monosaccharide units bonded together.
Formation: Disaccharides are formed via a dehydration synthesis reaction that creates a glycosidic linkage between two monosaccharides.
Common Types: Key disaccharides include sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (glucose + glucose).
Digestion: The body breaks down disaccharides into single sugar units using specific enzymes before they can be absorbed and used for energy.
Health Implications: Enzyme deficiencies, such as lactase deficiency, can lead to conditions like lactose intolerance due to the inability to digest certain disaccharides.
Versatility: The type of monosaccharides and the specific bond connecting them determine the disaccharide's properties, such as sweetness and how it is processed by the body.

What are carbs with two sugars called?

Carbohydrates composed of two single sugar units, or monosaccharides, joined together are known as disaccharides. The prefix "di-" means two, while "saccharide" is the chemical term for sugar, making the name a clear descriptor of its composition. These simple sugars are a major source of energy in many diets and include familiar examples like table sugar, milk sugar, and malt sugar.

The chemical process behind disaccharide formation

The creation of a disaccharide is a process known as dehydration synthesis, or a condensation reaction. This occurs when a hydroxyl group ($- ext{OH}$) from one monosaccharide and a hydrogen atom ($-H$) from another are removed to form a molecule of water ($H_2O$), leaving the two monosaccharides linked by an oxygen atom. This bond is specifically called a glycosidic linkage.

The nature of this glycosidic bond is crucial, as it determines the specific properties of the resulting disaccharide. For instance, the position and orientation of the bond can vary, leading to different molecules, even when the same monosaccharides are used. The human body requires specific enzymes, such as lactase and sucrase, to break these glycosidic bonds through a process called hydrolysis, which is the reverse of condensation, reintroducing a water molecule.

Common examples of disaccharides

Three of the most common and nutritionally significant disaccharides are sucrose, lactose, and maltose. They are found naturally in various foods and are composed of different monosaccharide pairs:

Sucrose: This is the common table sugar extracted from sugarcane and sugar beets. It is made up of one glucose unit and one fructose unit joined by an $\alpha-(1-2)$ glycosidic linkage.
Lactose: Known as "milk sugar," lactose is found in mammalian milk. It consists of one glucose unit and one galactose unit connected by a $\beta-(1-4)$ glycosidic bond. This particular bond is the reason why some people, who lack the enzyme lactase, are lactose intolerant.
Maltose: Malt sugar is a disaccharide made of two glucose units bonded together. It is found in germinating cereals like barley and is a product of starch breakdown.

Monosaccharides vs. disaccharides

Understanding the distinction between monosaccharides and disaccharides is key to grasping how our bodies process sugars.


Feature	Monosaccharides (Single Sugars)	Disaccharides (Double Sugars)
Number of Units	One sugar unit (e.g., glucose).	Two sugar units joined together.
Digestion	Absorbed directly into the bloodstream; no further digestion needed.	Broken down into monosaccharides by enzymes before absorption.
Examples	Glucose, fructose, galactose.	Sucrose, lactose, maltose.
Glycemic Impact	Generally cause a quicker spike in blood sugar.	Can cause a slightly less immediate spike than monosaccharides, as they require digestion.
Taste	Sweet taste.	Typically sweet taste, though varying in intensity (e.g., sucrose is sweeter than maltose).

The role of disaccharides in nutrition

Disaccharides are a primary source of energy for the body. Once broken down into their constituent monosaccharides in the small intestine, they are absorbed into the bloodstream. Glucose, in particular, is the body's main fuel source and is readily used by cells for energy. The presence of specific digestive enzymes, like lactase, sucrase, and maltase, is crucial for this process. A deficiency in any of these enzymes can lead to digestive issues, as seen with lactose intolerance.

Conclusion

Disaccharides, or carbohydrates with two sugar units, are a fundamental part of our diets and play a significant role in our energy metabolism. By understanding the composition and digestion of common disaccharides like sucrose, lactose, and maltose, consumers can make more informed choices about their nutritional intake. These double sugars are not only a source of quick energy but also a great example of the complex chemical processes that occur within our bodies to fuel our daily lives.

For more in-depth information on the structure and properties of these carbohydrates, the Biology Online guide to Disaccharides provides an excellent resource.

Frequently Asked Questions

A monosaccharide is a single sugar unit and is the most basic form of a carbohydrate, serving as the building block for more complex sugars like disaccharides and polysaccharides.

The most common examples of disaccharides are sucrose (table sugar), lactose (milk sugar), and maltose (malt sugar), which are found in a variety of foods.

The body breaks down disaccharides through a process called hydrolysis, which uses enzymes like lactase, sucrase, and maltase to split the double sugar into its two component monosaccharides.

Lactose intolerance occurs in people who have a deficiency of the enzyme lactase, which is needed to break down lactose into glucose and galactose. Without lactase, the undigested lactose ferments in the gut, causing digestive discomfort.

Disaccharides are simple carbohydrates made of two sugar units, while complex carbohydrates, such as starches, are composed of many sugar units and take longer to digest.

A glycosidic bond is the covalent bond that links two monosaccharide units together to form a disaccharide, created by the removal of a water molecule in a condensation reaction.

While many disaccharides, like sucrose, are sweet, their level of sweetness can vary. Some, like maltose, are less sweet, while others like cellobiose are only slightly sweet and indigestible by humans.