Polysaccharides are large, complex carbohydrates composed of many smaller sugar units. These molecules, such as starch or glycogen, serve as significant energy storage. For humans, these complex structures must be broken down into simpler, usable units to extract energy. This breakdown is facilitated by enzymes, biological catalysts.
The Main Enzymes
The primary enzymes breaking down polysaccharides in humans are amylases. Salivary amylase in saliva initiates starch digestion by cleaving long chains into smaller disaccharides. Pancreatic amylase from the pancreas continues this in the small intestine, breaking down remaining starch into disaccharides.
Other enzymes, disaccharidases, digest these smaller sugar molecules. These include maltase, sucrase, and lactase, which convert disaccharides into single sugar units (monosaccharides) like glucose, fructose, and galactose.
For dietary fiber like cellulose, the human body does not produce cellulase for digestion. Instead, gut bacteria possess enzymes to break down cellulose and other fibers through microbial fermentation. Bacterial activity converts indigestible compounds into absorbable short-chain fatty acids.
How Polysaccharides Are Broken Down in the Body
Polysaccharide digestion begins in the mouth, where chewing mechanically breaks down food and mixes it with salivary amylase. This enzyme starts starch breakdown into smaller carbohydrate chains. This initial digestion is brief.
As food moves from the mouth to the stomach, its acidic environment inactivates salivary amylase, halting activity. Minimal carbohydrate digestion occurs in the stomach.
The main site for extensive polysaccharide breakdown is the small intestine. Pancreatic amylase is released from the pancreas into the duodenum, continuing starch breakdown into disaccharides. Disaccharidases on the small intestinal lining break down these disaccharides into absorbable monosaccharides. These single sugar units are then absorbed into the bloodstream.
The Importance of Polysaccharide Digestion
Polysaccharide breakdown is fundamental because it releases glucose. Glucose is the main sugar in the blood and serves as the body’s primary energy source, fueling cellular functions including brain and muscle activity. Once digested into glucose, this simple sugar is absorbed into the bloodstream and distributed to cells for immediate energy use or storage.
While human enzymes do not digest all polysaccharides, dietary fiber plays a distinct role in gut health. Fiber passes mostly intact through the small intestine and reaches the large intestine, where it is fermented by beneficial gut bacteria. This fermentation supports a healthy gut microbiome and contributes to digestive well-being.