What Type of Sugar is Starch? Understanding Complex Carbohydrates

December 4, 2025 •

4 min read

The majority of carbohydrates in a typical diet, including those from foods like potatoes and grains, are in the form of starch. While fundamentally composed of sugar units, the question of what type of sugar is starch is best answered by classifying it as a complex carbohydrate, or polysaccharide.

Quick Summary

Starch is a complex carbohydrate (polysaccharide) composed of long chains of glucose units, a far cry from simple sugars. This structural complexity means it provides a slower, more sustained release of energy.

Key Points

Starch is a Polysaccharide: Starch is a complex carbohydrate made from many glucose molecules bonded together.
Not a Simple Sugar: Unlike simple sugars (monosaccharides and disaccharides), starch has a more complex structure and is not sweet.
Composed of Glucose: The fundamental building block of starch is the simple sugar glucose, linked together in long chains.
Two Main Forms: Starch is comprised of two distinct molecules: amylose (linear) and amylopectin (branched).
Slower Digestion: The complex structure of starch means it is digested more slowly than simple sugars, leading to a gradual release of glucose into the bloodstream.
Energy Storage in Plants: Plants create and store excess glucose as starch for future energy needs.
Source of Energy for Humans: Our bodies use enzymes like amylase to break down dietary starch into glucose for fuel.

Starch: A Polysaccharide, Not a Simple Sugar

To accurately answer the question, "What type of sugar is starch?", we must first understand the classification of carbohydrates. Carbohydrates are broadly grouped into three categories: sugars (simple carbohydrates), starches (complex carbohydrates), and fiber. Unlike simple sugars, which consist of one or two sugar molecules, starch is a polysaccharide, meaning it is made from many glucose units chained together. This polymeric structure has a significant impact on its physical properties and how the human body processes it. While the building blocks are simple sugars (glucose), the overall molecule is complex, which is why it does not taste sweet and takes longer to digest.

The Two Molecular Forms of Starch: Amylose and Amylopectin

Starch isn't a single, monolithic molecule but rather a mixture of two different polysaccharides: amylose and amylopectin. Most plants contain a ratio of both, which contributes to the starch's overall properties.

Amylose: This is the linear, helical form of starch, consisting of hundreds of glucose molecules joined together in a straight chain. Amylose is less soluble in water and is more resistant to digestion, making it a type of resistant starch.
Amylopectin: This is the branched, tree-like structure of starch, comprising thousands of glucose units. The numerous branch points allow digestive enzymes to access and break down the glucose units much more rapidly, making amylopectin more soluble and easily digestible than amylose.

The Digestive Journey: From Complex Chains to Simple Glucose

When we consume starch-rich foods like potatoes, rice, or bread, the digestive process begins immediately. Enzymes are responsible for breaking down the large starch molecules into individual glucose units that can be absorbed by the body.

Here is a step-by-step breakdown of the process:

Oral Phase: In the mouth, salivary alpha-amylase begins to break the chemical bonds within the starch, converting some of it into smaller sugar fragments.
Gastric Phase: In the stomach, the acidic environment inhibits salivary amylase. However, for some foods, the starch digestion initiated in the mouth can continue for a while until the pH becomes too low.
Intestinal Phase: The primary digestion of starch occurs in the small intestine. Pancreatic alpha-amylase is secreted, further breaking down the remaining starch into smaller sugar molecules, primarily maltose. Enzymes on the brush border of the intestinal lining, such as maltase and isomaltase, then finish the job, converting these smaller sugars into absorbable glucose.

Starch vs. Simple Sugars: A Comparative Look

Understanding the fundamental differences between starch and simple sugars is crucial for grasping their distinct nutritional impacts. The following table highlights the key characteristics of each.


Feature	Starch (Complex Carbohydrate)	Simple Sugars (Simple Carbohydrate)
Molecular Structure	Long chains of glucose molecules (polysaccharide).	Single (monosaccharide) or double (disaccharide) sugar molecules.
Taste	Generally tasteless in its pure form.	Sweet to the taste.
Digestion Speed	Takes longer to digest due to its complex structure.	Digested and absorbed very quickly.
Energy Release	Provides a slow, sustained release of glucose into the bloodstream.	Causes a rapid spike and subsequent crash in blood sugar and energy levels.
Sources	Grains, potatoes, beans, lentils.	Fruit, milk, processed foods, candy, soda.
Nutritional Profile	Often found in foods containing fiber, vitamins, and minerals.	Often provides "empty calories" with little to no other nutrients.

Starch in the Context of a Healthy Diet

Far from being an unhealthy food group, complex carbohydrates from starchy foods are a vital part of a balanced diet. The slow digestion of starch helps provide a steady supply of energy for the body and brain, avoiding the rapid blood sugar fluctuations associated with simple sugars. Additionally, many starchy foods, especially whole grains and tubers, come packaged with essential vitamins, minerals, and dietary fiber, which is beneficial for digestive health. Not all starches are created equal, however. The way food is processed and prepared can affect its digestibility. For instance, some starches in uncooked or cooled foods are resistant to digestion and act like dietary fiber, offering prebiotic benefits. Learn more about the biology of carbohydrates at the Khan Academy website.

Conclusion: Starch is a Complex Form of Sugar

In summary, while starch is chemically derived from glucose, a simple sugar, it is not a simple sugar itself. It is a complex carbohydrate, or polysaccharide, whose multi-unit structure dictates a slower, more gradual digestion process compared to simple sugars. This provides sustained energy for the body and is a cornerstone of a healthy diet. Understanding this fundamental difference is key to making informed nutritional choices and appreciating the different roles that various types of carbohydrates play in our health.

Frequently Asked Questions

No, starch is a complex carbohydrate, or polysaccharide. Sugar typically refers to simple carbohydrates like monosaccharides and disaccharides, which have a much simpler molecular structure.

The key difference lies in their molecular complexity. Sugar molecules are small and simple, whereas starch is a long chain of many sugar molecules bonded together, which makes it complex.

The fundamental building blocks of starch are glucose molecules. Starch is formed by linking many glucose units together through glycosidic bonds.

The body uses enzymes called amylase, found in saliva and the pancreas, to break down starch into glucose molecules during digestion.

Complex carbohydrates like starch are an important part of a healthy diet. They provide a steady release of energy and are often found in nutrient-rich foods. The key is to choose whole food sources rather than heavily processed ones.

Starch is produced by green plants during photosynthesis to store excess glucose for future energy needs. It is typically found in roots, seeds, and tubers.

Starch is a polysaccharide, meaning its multiple sugar units are bound together in long chains. This structure prevents the individual glucose units from interacting with sweet taste receptors on the tongue.

Amylose is a linear chain of glucose molecules, while amylopectin is a highly branched chain. This structural difference affects their solubility and digestibility.