What are the four types of sugars and how do they differ?

November 11, 2025 •

2 min read

According to the American Heart Association, added sugars are the number one source of added calories in the American diet, but not all sugars are the same. This guide explains what are the four types of sugars—glucose, fructose, sucrose, and and lactose—and their key differences.

Quick Summary

This article details the four main types of simple sugars: glucose (blood sugar), fructose (fruit sugar), sucrose (table sugar), and lactose (milk sugar). It explores their individual characteristics, dietary sources, and how they function within the human body.

Key Points

Glucose is the Body's Primary Fuel: This monosaccharide is the main source of energy for your body's cells and is also known as blood sugar.
Fructose is Fruit Sugar: This monosaccharide is found naturally in fruits and honey, and is the sweetest of the natural sugars.
Sucrose is Table Sugar: A disaccharide made of glucose and fructose, sucrose is derived from sugarcane and sugar beets.
Lactose is Milk Sugar: This disaccharide consists of glucose and galactose and is found exclusively in milk and dairy products.
Natural vs. Added Sugars Matter: The context in which sugar is consumed is critical; sugars from whole foods come with beneficial nutrients, unlike added sugars in processed products.
Digestion Varies: Monosaccharides like glucose and fructose are absorbed directly, while disaccharides like sucrose and lactose must first be broken down by enzymes.

Understanding the Basics of Sugar

Sugar is a general term for soluble carbohydrates and is categorized by its chemical structure. Monosaccharides are 'single sugar' molecules, while disaccharides are formed when two monosaccharides link. The four common simple sugars in our diets are two monosaccharides and two disaccharides, each with distinct roles and sources.

1. Glucose (The Body's Main Fuel)

Glucose, a monosaccharide, is the primary energy source transported in the blood for cells, often called 'blood sugar'. It is found in fruits, vegetables, honey, and produced when the body breaks down complex carbohydrates. Insulin helps glucose enter cells for energy.

2. Fructose (Fruit Sugar)

Fructose is a monosaccharide found in fruits, honey, and root vegetables. It is processed mainly in the liver, where it can be converted to glucose or fat.

3. Sucrose (Table Sugar)

Sucrose, a disaccharide of glucose and fructose, is common table sugar derived from sugarcane and sugar beets. It is broken down into glucose and fructose in the small intestine for absorption.

4. Lactose (Milk Sugar)

Lactose is a disaccharide of galactose and glucose, found only in milk and dairy. The enzyme lactase is needed to break down lactose, and many adults have insufficient lactase, causing lactose intolerance.

Natural vs. Added Sugars

Sugars occur naturally in whole foods like fruits and milk, providing nutrients like fiber. Added sugars are included during processing and lack these benefits, often found in drinks and snacks.

Comparison Table of Four Key Sugars


Characteristic	Glucose	Fructose	Sucrose	Lactose
Classification	Monosaccharide	Monosaccharide	Disaccharide (Glucose + Fructose)	Disaccharide (Glucose + Galactose)
Sources	Fruits, vegetables, corn syrup, breakdown of other carbs	Fruits, honey, high-fructose corn syrup	Sugarcane, sugar beets, many fruits and vegetables	Milk and dairy products
Digestion	Absorbed directly into bloodstream	Primarily processed by the liver	Broken down into glucose and fructose by sucrase	Broken down into glucose and galactose by lactase
Relative Sweetness	Less sweet than sucrose	Sweetest of the natural sugars	Standard for comparison	Least sweet of the four
Primary Function	Main energy source for body's cells	Metabolized in the liver; can be converted to glucose or fat	Source of energy once broken down	Provides energy in milk for infants

Conclusion

Understanding glucose, fructose, sucrose, and lactose is key to understanding carbohydrate use in the body. These simple sugars provide energy, but their structure and sources affect digestion and metabolism. The health impact of naturally occurring sugars in whole foods differs significantly from added sugars in processed items due to accompanying nutrients. Choosing a diet rich in fruits, vegetables, and whole grains provides essential carbohydrates, while consuming added sugars in moderation is advised for health.

Frequently Asked Questions

The four main types of simple sugars are glucose (blood sugar), fructose (fruit sugar), sucrose (table sugar), and lactose (milk sugar). Glucose and fructose are single-molecule sugars (monosaccharides), while sucrose and lactose are double-molecule sugars (disaccharides).

Glucose is found in fruits and honey, and is the result of digesting carbohydrates. Fructose is found in fruits and honey. Sucrose is derived from sugarcane and sugar beets. Lactose is found exclusively in milk and dairy products.

Sugars from whole fruits and vegetables come packaged with fiber, vitamins, and minerals, which slows digestion and provides more health benefits. Added sugars lack these nutrients. While the sugars themselves are chemically similar, the nutritional context of the food source is very different.

Glucose is a monosaccharide, a single sugar unit. Sucrose is a disaccharide, meaning it is made of two monosaccharides bonded together: one glucose molecule and one fructose molecule.

Lactose intolerance is the inability to fully digest lactose, the sugar found in milk. It occurs when a person does not produce enough of the enzyme lactase, which is required to break down lactose into glucose and galactose for absorption.

No, while sugars are a type of carbohydrate, not all carbohydrates are sugars. Carbohydrates are broadly classified into simple carbohydrates (monosaccharides and disaccharides) and complex carbohydrates (polysaccharides, like starch and fiber).

No, honey and table sugar (sucrose) are different, though both are sweeteners. Honey is primarily a mix of the monosaccharides fructose and glucose, while table sugar is the disaccharide sucrose (one molecule of glucose bonded to one of fructose).