What carbohydrates are made up of many sugar units? A Guide to Polysaccharides

January 11, 2026 •

4 min read

According to the MSD Manuals, polysaccharides are chains of 10 or more sugar molecules linked together. These complex carbohydrates, also known as starches and fibers, are made up of many sugar units, or monosaccharides, and are a fundamental component of diet and biological function.

Quick Summary

Polysaccharides are complex carbohydrates consisting of long chains of sugar units called monosaccharides. They are crucial for energy storage in living organisms and provide structural support, with key examples including starch, glycogen, and cellulose.

Key Points

Polysaccharides: These are carbohydrates made up of many sugar units, distinguishing them from simple monosaccharides and disaccharides.
Energy Storage: In plants, starch is the energy storage polysaccharide, while in animals, this role is filled by glycogen.
Structural Role: Cellulose provides structural support in plant cell walls and acts as dietary fiber for humans because we cannot digest it.
Sustained Energy: The complex structure of polysaccharides leads to slow digestion, offering a gradual and sustained release of energy, unlike simple sugars.
Dietary Fiber: Indigestible polysaccharides, such as cellulose, are known as dietary fiber and are essential for a healthy digestive system.
Healthy Sources: Whole grains, legumes, and starchy vegetables are excellent sources of complex carbohydrates and also provide vital vitamins, minerals, and fiber.

Polysaccharides: The Structure of Complex Carbohydrates

Polysaccharides are large macromolecules composed of long chains of monosaccharide units, or simple sugars, linked together by glycosidic bonds. The term "polysaccharide" literally means "many sugars," contrasting with monosaccharides ("one sugar") and disaccharides ("two sugars"). This complex structure is the key difference between simple and complex carbohydrates, and it dictates how the body processes and utilizes them. The arrangement and type of these bonds determine the properties of the polysaccharide, such as its shape, solubility, and digestibility.

Key Functions of Polysaccharides

Polysaccharides play several critical roles in living organisms, performing functions that simple sugars cannot.

Energy Storage: They act as a compact, efficient way for both plants and animals to store energy. When energy is needed, the body breaks down these long chains back into individual glucose molecules.
Structural Support: In plants and other organisms, they provide rigid structural support. The fibrous nature of some polysaccharides is essential for forming cell walls and exoskeletons.
Dietary Fiber: For humans, some polysaccharides are indigestible and pass through the digestive system as dietary fiber. This fiber is essential for maintaining gut health, aiding digestion, and regulating blood sugar.
Cellular Communication: Polysaccharides can also bond with lipids and proteins to form glycoconjugates, which are crucial for cellular communication and signaling.

Major Types of Polysaccharides

Different organisms create and use various types of polysaccharides for specific purposes. The most important examples include starch, glycogen, and cellulose.

Starch Starch is the primary energy storage polysaccharide in plants. It is abundant in foods such as potatoes, rice, corn, and wheat, making it a major source of dietary carbohydrates for humans. Starch is a mixture of two glucose polymers: amylose and amylopectin. Amylose is a linear, unbranched chain of glucose units, while amylopectin is highly branched. The highly branched structure of amylopectin allows for quicker access to glucose when plants need energy.

Glycogen Often called "animal starch," glycogen is the primary energy storage polysaccharide in animals. It is stored mainly in the liver and muscle cells. Similar in structure to amylopectin, glycogen is an even more highly branched polymer of glucose. This extensive branching creates numerous endpoints, allowing enzymes to quickly release glucose into the bloodstream to meet sudden energy demands, such as during exercise.

Cellulose Cellulose is a structural polysaccharide that forms the cell walls of plants. It is the most abundant organic molecule on Earth. Unlike starch and glycogen, cellulose is an unbranched polymer of glucose linked by beta-glycosidic bonds. This linkage is crucial, as human digestive enzymes cannot break it down, making cellulose indigestible. For this reason, cellulose functions as dietary fiber in the human diet.

Chitin Chitin is a structural polysaccharide found in the exoskeletons of arthropods, such as insects and crustaceans, as well as in the cell walls of some fungi. It is similar in structure to cellulose but contains nitrogen-containing side branches, which increase its strength.

Digestion and Nutritional Role

How the body digests a carbohydrate is directly related to its molecular structure. Simple carbohydrates, with only one or two sugar units, are digested and absorbed quickly, causing a rapid rise in blood sugar. Polysaccharides, with their long chains, take much longer to break down. This slow digestion results in a gradual release of glucose into the bloodstream, providing sustained energy and helping to maintain stable blood sugar levels.

Refined grains, like white bread and white rice, have been processed to remove fiber and other nutrients, leaving behind easily digestible complex carbohydrates that behave more like simple sugars. In contrast, whole grains retain their fiber and nutrients, offering the benefits of slow digestion. The indigestible polysaccharides, like cellulose, act as dietary fiber, which aids digestive health, promotes feelings of fullness, and can help manage weight. For more detailed information on the health benefits of complex carbohydrates, visit the American Heart Association.

Comparison of Major Polysaccharides


Feature	Starch	Glycogen	Cellulose
Function	Energy storage in plants	Energy storage in animals	Structural support in plants
Location	Seeds, roots, and tubers	Liver and muscle cells	Plant cell walls
Structure	Linear (amylose) and branched (amylopectin) glucose chains	Highly branched glucose chains	Linear, unbranched glucose chains
Digestibility	Digestible by humans	Digestible by humans	Indigestible by humans (dietary fiber)
Constituent Units	Glucose	Glucose	Glucose

The Importance of Making Smart Choices

Choosing whole, minimally processed sources of complex carbohydrates is crucial for maximizing their nutritional benefits. While processed foods often strip away valuable nutrients, whole-food sources deliver a package of vitamins, minerals, and dietary fiber along with the sustained energy release. Opting for whole grains, legumes, and vegetables over refined sugars and starches is key for a balanced diet and long-term health.

Conclusion

In summary, polysaccharides are the carbohydrates made up of many sugar units, forming long, complex chains. They are distinct from simple sugars and are categorized by their function: energy storage (starch in plants, glycogen in animals) and structural support (cellulose in plants, chitin in exoskeletons). The complex structure of polysaccharides means they are digested slowly, providing sustained energy, fiber for gut health, and essential nutrients. By prioritizing whole-food sources of these complex carbohydrates, individuals can significantly improve their overall dietary health and well-being.

Frequently Asked Questions

The main difference is their molecular size and structure. Simple carbohydrates are made of one or two sugar units, which are digested quickly. Complex carbohydrates, or polysaccharides, are long chains of many sugar units that take longer to digest, providing sustained energy.

The three main types of polysaccharides are starch, glycogen, and cellulose. Starch stores energy in plants, glycogen stores energy in animals, and cellulose provides structural support in plant cell walls.

Humans cannot digest cellulose because our bodies lack the necessary enzymes to break the specific beta-glycosidic bonds that link the glucose units in its structure. It therefore passes through our system as dietary fiber.

In the human body, glycogen is primarily stored in the liver and muscle cells. It acts as a readily available energy reserve that can be quickly mobilized when needed.

Not all complex carbohydrates are equally healthy. While sources like whole grains and vegetables are very nutritious, refined grains are processed to remove fiber and nutrients. It's best to prioritize whole-food sources.

No, polysaccharides are generally not sweet. The sweet taste in carbohydrates comes from simple sugars like glucose and fructose, while the large, complex structure of polysaccharides removes this property.

Indigestible polysaccharides, or dietary fiber, pass intact through the small intestine. They reach the large intestine, where they can be fermented by gut bacteria, contributing to digestive health.

Food sources rich in polysaccharides include whole grains (oats, brown rice), legumes (beans, lentils), starchy vegetables (potatoes, sweet potatoes), and fruits and vegetables that contain dietary fiber.