Are Polysaccharides Hard to Break Down?

January 12, 2026 •

4 min read

According to the National Institutes of Health, complex carbohydrates like polysaccharides take longer to digest compared to simple sugars. This process is influenced by a variety of factors, including the molecule's size, its chemical structure, and the presence of specific enzymes in the digestive system, which together answer the question: are polysaccharides hard to break down?.

Quick Summary

The digestibility of polysaccharides, or complex carbohydrates, varies widely due to differences in molecular size, branching, and specific chemical bonds. Some, like starch, are broken down by human enzymes, while others, like cellulose, resist human digestion and are instead fermented by gut bacteria.

Key Points

Molecular Size: Polysaccharides are much larger molecules than simple sugars, which is the primary reason they are harder to break down and take longer to digest.
Bond Type Matters: Human enzymes can break the alpha-glycosidic bonds in starch and glycogen, but not the beta-glycosidic bonds in cellulose, making cellulose indigestible.
Enzymes are Essential: The digestive system relies on specific enzymes like amylase to hydrolyze polysaccharides like starch into smaller, absorbable units.
Gut Microbes Help Digestion: Indigestible polysaccharides, such as dietary fiber, are fermented by beneficial bacteria in the large intestine, producing vital short-chain fatty acids.
Structure and Branching: The degree of branching in a polysaccharide, such as the extensive branching in glycogen, can affect the speed of its digestion.
Food Matrix Impact: Food processing, solubility, and the physical structure of the plant cell walls can significantly influence the overall digestibility of polysaccharides.

The Core Challenge: Molecular Complexity

Polysaccharides are polymers of monosaccharides, which means they consist of long, intricate chains of simple sugar units linked together by glycosidic bonds. This large and complex molecular structure is the primary reason that polysaccharides are more difficult and time-consuming to break down than simple sugars (monosaccharides or disaccharides). A monosaccharide like glucose can be absorbed directly by the body, but polysaccharides must first be dismantled into these smaller, absorbable units. This enzymatic breakdown process is influenced by several critical factors.

The Role of Glycosidic Bonds and Branching

The type of glycosidic bond linking the sugar units is a fundamental determinant of digestibility. Humans possess enzymes, particularly amylase, that can break the alpha-glycosidic bonds found in starch, allowing it to be digested relatively efficiently. However, humans lack the necessary enzymes, like cellulase, to break the beta-glycosidic bonds present in cellulose. This is why cellulose, a polysaccharide found in plant cell walls, passes through the human digestive system largely undigested and is known as dietary fiber.

Branching also plays a significant role. Glycogen, the energy storage polysaccharide in animals, is more densely branched than plant starch. This extensive branching provides more non-reducing ends for enzymes to act upon simultaneously, allowing for faster degradation when the body needs a rapid energy release. Conversely, less-branched or linear polysaccharides can be more slowly broken down.

A Comparison of Digestible vs. Indigestible Polysaccharides

To better understand why some polysaccharides are hard to break down, a comparison of different types is useful.


Feature	Starch (Amylose and Amylopectin)	Glycogen	Cellulose	Inulin
Molecular Structure	Linear (amylose) and branched (amylopectin) chain of glucose units.	Highly branched chain of glucose units.	Linear, unbranched chain of beta-glucose units.	Chain of fructose units.
Bond Type	Alpha-glycosidic bonds.	Alpha-glycosidic bonds.	Beta-glycosidic bonds.	Beta-glycosidic bonds.
Digestibility in Humans	Readily digested by amylase enzymes.	Readily digested by amylase enzymes; faster due to extensive branching.	Indigestible by human enzymes; passes through as dietary fiber.	Indigestible by human enzymes; fermented by gut bacteria.
Primary Function	Energy storage in plants.	Energy storage in animals.	Structural support in plants.	Energy storage in some plants.
Breakdown Mechanism	Enzymatic hydrolysis by salivary and pancreatic amylase.	Enzymatic hydrolysis by amylase.	Fermentation by bacteria in the large intestine.	Fermentation by bacteria in the large intestine.

The Role of the Gut Microbiome

For polysaccharides that human enzymes cannot break down, the gut microbiome becomes a crucial player. Trillions of microbes, including bacteria, residing in the colon, possess a vast array of carbohydrate-active enzymes (CAZymes) that can break down complex polysaccharides like dietary fiber. This process of microbial fermentation produces short-chain fatty acids (SCFAs), which serve as an energy source for colon cells and have numerous benefits for overall health.

Key takeaways on microbial fermentation:

Host-microbe symbiosis: Humans and their gut bacteria have a mutually beneficial relationship. We provide food (indigestible polysaccharides), and they provide us with beneficial metabolites (SCFAs).
Impact on health: A diverse range of polysaccharides, such as those found in fruits and vegetables, fosters a diverse and healthy gut microbiome.
Individual variation: The composition of a person's gut microbiome can vary significantly and affects how effectively different types of dietary fiber are fermented.

Factors Affecting Overall Digestibility

Beyond the intrinsic molecular properties, external factors influence how hard polysaccharides are to break down:

Food Processing: Cooking and processing can alter the structure of plant cell walls, making embedded starches more accessible to digestive enzymes. For example, cooking starches causes them to gelatinize, increasing their digestibility. Conversely, processing that keeps plant cell walls intact, such as in whole grains or legumes, can slow down digestion.
Physical Structure: The matrix of the food itself plays a part. Nutrients within intact plant cell walls are less bioavailable as enzymes cannot easily penetrate the rigid structure.
Solubility and Viscosity: Soluble fibers, such as those found in oats (beta-glucan), can increase the viscosity of the contents of the digestive tract. This slows down the mixing of food and the diffusion of enzymes, thus reducing the speed of digestion and nutrient absorption.

Conclusion: A Multi-faceted Process

The answer to "are polysaccharides hard to break down?" is nuanced. While all polysaccharides require more effort to break down than simpler sugars due to their larger size and more complex structure, their ultimate fate in the human body depends on specific structural details, particularly the type of glycosidic bonds. Digestible polysaccharides like starch are broken down by human enzymes, though at a slower pace than simple sugars. Indigestible ones, known as dietary fiber (e.g., cellulose and inulin), cannot be processed by human enzymes and are fermented by beneficial gut bacteria. The hardness of a polysaccharide's digestion is, therefore, a key factor that shapes not only our energy metabolism but also the health of our gut microbiome.

For more information on the structural properties of these complex molecules, the Wikipedia entry on Polysaccharides provides a comprehensive overview.

Frequently Asked Questions

Polysaccharides are large, complex molecules made of many sugar units joined together. In contrast, monosaccharides are single sugar units. The large size and intricate structure of polysaccharides require more time and specific enzymes to break them down into smaller, absorbable units.

No, humans cannot digest all types of polysaccharides. We can digest polysaccharides with alpha-glycosidic bonds, like starch, using enzymes such as amylase. However, we lack the necessary enzymes to break the beta-glycosidic bonds found in cellulose, which is why it passes through the digestive system as dietary fiber.

Starch is composed of glucose units linked by alpha-glycosidic bonds, which are easily broken by human amylase. Cellulose is made of glucose units linked by beta-glycosidic bonds, which humans cannot break. Therefore, starch is digested for energy, while cellulose acts as indigestible dietary fiber.

The human gut microbiome contains trillions of bacteria that possess a vast range of enzymes capable of fermenting polysaccharides that human enzymes cannot digest. This process of microbial fermentation breaks down dietary fiber and produces beneficial short-chain fatty acids.

Food processing methods like cooking can disrupt rigid plant cell walls, making the starches and other polysaccharides they contain more accessible to human digestive enzymes. However, other factors like the food's physical structure and a polysaccharide's solubility can still affect the speed of digestion.

Yes, highly branched polysaccharides, such as glycogen, can be broken down more quickly than linear ones. This is because the multiple branches provide more points for digestive enzymes to act upon simultaneously, accelerating the breakdown process.

You can support the digestion and fermentation of polysaccharides by eating a diet rich in a variety of dietary fibers from different sources, as this supports a diverse and healthy gut microbiome. A diverse microbiome is better equipped to ferment a wider range of indigestible polysaccharides.