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Reducing Sugar vs. Starch: What's the Difference?

Edited by Aimie Carlson || By Harlon Moss || Published on December 18, 2023
Reducing sugars, like glucose and fructose, can donate electrons during chemical reactions, whereas starches are long-chain polysaccharides that cannot.

Key Differences

Reducing sugars are carbohydrates that can act as reducing agents due to their free aldehyde or ketone groups. Examples include glucose and fructose. Starch, conversely, is a polysaccharide composed of numerous glucose units, primarily found in plants as an energy storage molecule.
The structure of reducing sugars allows them to participate in oxidation-reduction reactions, changing the oxidation state of other compounds. Starch is more complex, consisting of two types of molecules: amylose and amylopectin, and does not readily participate in such reactions.
Reducing sugars are often found in various fruits and honey, and they play a vital role in browning processes in food, like caramelization. Starch is a key component in foods like potatoes, rice, and bread, providing a significant source of energy.
From a nutritional standpoint, reducing sugars are quickly absorbed and used by the body, contributing to immediate energy needs. Starch is digested more slowly, providing a more sustained energy release.
In laboratory tests, reducing sugars can be identified using specific chemical reactions, such as the Benedict's test, which gives a positive result for these sugars. Starch can be identified using the iodine test, where it turns a dark blue or black color.

Comparison Chart

Chemical Structure

Simple sugars with free aldehyde or ketone groups
Long-chain polysaccharides


Can act as reducing agents
Does not act as reducing agent


Fruits, honey
Potatoes, rice, bread

Role in Food

Involved in browning and caramelization
Thickening agent, energy source

Digestion and Absorption

Rapidly absorbed and metabolized
Slow digestion, sustained energy release

Reducing Sugar and Starch Definitions

Reducing Sugar

A sugar capable of acting as a reducing agent.
Glucose, a reducing sugar, is crucial for cellular energy.


Used by plants for energy storage.
Starch in grains is a major energy source for humans.

Reducing Sugar

Contains free aldehyde or ketone groups.
Fructose, a common reducing sugar, is found in many fruits.


Consists of amylose and amylopectin.
The structure of starch affects its digestibility.

Reducing Sugar

Participates in redox reactions.
Reducing sugars like lactose are present in dairy products.


Turns blue-black with iodine.
The iodine test for starch is a common classroom experiment.

Reducing Sugar

Detected by specific chemical tests.
Reducing sugars give a positive Benedict's test result.


A key thickener in cooking.
Starch is used to thicken sauces and gravies.

Reducing Sugar

Plays a role in food browning.
The browning of cakes is partly due to reducing sugars.


A polysaccharide composed of glucose units.
Starch is abundant in foods like potatoes.


A naturally abundant nutrient carbohydrate, (C6H10O5)n, found chiefly in the seeds, fruits, tubers, roots, and stem pith of plants, notably in corn, potatoes, wheat, and rice, and varying widely in appearance according to source but commonly prepared as a white amorphous tasteless powder.


Any of various substances, such as natural starch, used to stiffen cloth, as in laundering.


What is a reducing sugar?

Reducing sugars are sugars that can donate electrons in redox reactions.

What is starch primarily used for?

Starch is used as an energy storage molecule in plants and a food source for humans.

Can reducing sugars be identified through testing?

Yes, reducing sugars can be identified using tests like Benedict's test.

Can starch act as a reducing agent?

No, starch cannot act as a reducing agent due to its structure.

Is starch easily digestible?

Starch digestion varies based on its structure but is generally slower than sugar digestion.

What is the main component of starch?

Starch is mainly composed of long chains of glucose units.

What role do reducing sugars play in the body?

Reducing sugars are quickly metabolized for energy in the body.

How are reducing sugars different from non-reducing sugars?

Reducing sugars have free aldehyde or ketone groups, allowing them to act as reducing agents, unlike non-reducing sugars.

What foods are high in reducing sugars?

Fruits and honey are typically high in reducing sugars.

How do reducing sugars contribute to food flavor?

Reducing sugars participate in caramelization and Maillard reactions, contributing to flavor development in foods.

Do all carbohydrates act as reducing sugars?

Not all carbohydrates are reducing sugars; it depends on their specific chemical structure.

How is starch used in cooking?

Starch is commonly used as a thickening agent in sauces and gravies.

Are there health concerns with consuming too much starch?

Excessive starch intake can lead to weight gain and related health issues.

Is starch found in animal products?

Starch is primarily found in plant products, not in animal products.

How do reducing sugars affect food preservation?

Reducing sugars can influence food preservation, particularly in processes like jam-making and canning.

Can reducing sugars be used in baking?

Yes, reducing sugars are often used in baking for their caramelization properties.

What type of foods contain a high amount of starch?

Foods like potatoes, rice, and bread are high in starch.

Is starch a type of sugar?

Starch is a polysaccharide made of sugar units, but it's not a sugar itself.

How does the body process reducing sugars?

The body rapidly absorbs and utilizes reducing sugars for energy.

Can starch be broken down into reducing sugars?

Yes, through digestion and certain processes, starch can be broken down into reducing sugars.
About Author
Written by
Harlon Moss
Harlon is a seasoned quality moderator and accomplished content writer for Difference Wiki. An alumnus of the prestigious University of California, he earned his degree in Computer Science. Leveraging his academic background, Harlon brings a meticulous and informed perspective to his work, ensuring content accuracy and excellence.
Edited by
Aimie Carlson
Aimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.

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