What Digestive Enzyme Digests Sugar and Other Carbohydrates?

January 7, 2026 •

4 min read

In humans, the brush border enzyme sucrase is responsible for breaking down the common sugar sucrose (table sugar) into absorbable glucose and fructose. This vital process is part of a complex system of carbohydrate digestion that involves several specific enzymes acting at different stages, from the mouth to the small intestine.

Quick Summary

Several specific enzymes, including sucrase, lactase, and amylase, break down various sugars and carbohydrates in the digestive tract. The process starts in the mouth, is continued by pancreatic enzymes, and is completed by brush border enzymes in the small intestine, allowing nutrient absorption.

Key Points

Sucrase is the primary enzyme for table sugar: The brush border enzyme sucrase specifically breaks down sucrose into absorbable glucose and fructose in the small intestine.
Carbohydrate digestion is a multi-stage process: It begins in the mouth with salivary amylase, continues in the small intestine with pancreatic amylase, and concludes with specialized brush border enzymes.
Different enzymes target different sugars: Amylase breaks down starches, lactase breaks down lactose (milk sugar), and maltase breaks down maltose.
The brush border is the finishing line: The final enzymatic action that turns disaccharides into absorbable monosaccharides occurs on the microvilli of the small intestine.
Enzyme deficiencies cause malabsorption: A lack of specific enzymes, like lactase or sucrase, leads to undigested sugars reaching the large intestine, causing gas, bloating, and diarrhea.
The pancreas is a major contributor: This organ releases pancreatic amylase into the small intestine to further break down complex starches into smaller sugars.
Undigested sugars are fermented by bacteria: When enzymes are insufficient, the body cannot absorb the sugars, and they become food for bacteria in the colon, causing unpleasant digestive symptoms.

The Primary Sugar Digesting Enzyme: Sucrase

While multiple enzymes participate in carbohydrate breakdown, the digestion of sucrose, or common table sugar, is performed exclusively by the enzyme sucrase. More accurately known as sucrase-isomaltase, this enzyme is located on the microvilli of the cells lining the small intestine, a region referred to as the brush border. Sucrase-isomaltase specifically catalyzes the hydrolysis of sucrose, splitting it into its two simpler component monosaccharides: glucose and fructose. These simpler sugars are then absorbed into the bloodstream to be used as energy. Without sufficient sucrase, sucrose cannot be properly digested, a condition known as congenital sucrase-isomaltase deficiency (CSID), which leads to various digestive discomforts.

The Journey of Carbohydrate Digestion

Carbohydrate digestion is a multi-step process that begins the moment food enters the mouth and ends in the small intestine. This complex journey ensures that large, complex carbohydrate molecules are systematically broken down into simple, absorbable sugars.

Step 1: In the Mouth (Salivary Amylase)

The process of chemically breaking down carbohydrates begins in the mouth with the action of salivary amylase. As you chew, salivary glands secrete saliva containing this enzyme, which immediately starts hydrolyzing starches (long chains of glucose) into smaller carbohydrate chains and the disaccharide maltose. However, because food stays in the mouth for only a short time, this initial breakdown is limited.

Step 2: The Stomach Interlude

After swallowing, the food travels down the esophagus to the stomach. The highly acidic environment of the stomach effectively deactivates salivary amylase, halting the digestion of carbohydrates temporarily. While the stomach is a critical site for protein digestion, it plays a minimal role in carbohydrate processing.

Step 3: Completing Digestion in the Small Intestine

Upon entering the small intestine, the acidic chyme from the stomach is neutralized by bicarbonate released from the pancreas. This creates a more alkaline environment suitable for the next wave of enzymes.

Pancreatic Amylase: The pancreas releases pancreatic amylase into the small intestine. This powerful enzyme continues the breakdown of any remaining starches and smaller carbohydrate chains into maltose and other disaccharides.
Brush Border Enzymes: The final, crucial stage of carbohydrate digestion occurs at the brush border of the small intestine. This is where a suite of specialized enzymes, including sucrase, lactase, and maltase, are embedded in the microvilli. These enzymes tackle the last remaining disaccharides, breaking them down into monosaccharides that can be absorbed.

The Specialized Brush Border Enzymes

Each brush border enzyme has a specific function, acting like a lock and key to break down a particular type of sugar.

Lactase and Lactose Digestion

Lactase is the enzyme responsible for digesting lactose, the sugar found in milk and dairy products. It breaks down lactose into glucose and galactose. Insufficient lactase production leads to lactose intolerance, causing digestive symptoms like bloating and diarrhea when consuming dairy. Interestingly, lactase activity naturally decreases in many human populations after infancy.

Maltase and Maltose Breakdown

Maltase is another key brush border enzyme that digests maltose, a disaccharide often produced during the breakdown of starch by amylase. It splits each maltose molecule into two glucose molecules. Maltase activity is also crucial for digesting maltotriose and other small starch fragments.

The Role of the Pancreas

The pancreas plays a central role in carbohydrate digestion by producing and secreting pancreatic amylase. It ensures that complex starches are broken down efficiently in the small intestine into disaccharides like maltose. For individuals with conditions like exocrine pancreatic insufficiency, the pancreas may not produce enough amylase, impairing carbohydrate digestion and nutrient absorption.

A Comparison of Key Carbohydrate Enzymes


Enzyme	Substrate (Sugar)	Location	Breakdown Products
Amylase	Starches	Salivary Glands & Pancreas	Maltose & smaller carbohydrate chains
Sucrase	Sucrose (Table Sugar)	Small Intestine (Brush Border)	Glucose & Fructose
Lactase	Lactose (Milk Sugar)	Small Intestine (Brush Border)	Glucose & Galactose
Maltase	Maltose	Small Intestine (Brush Border)	Glucose

Consequences of Enzyme Deficiencies

When the body cannot produce enough of a specific digestive enzyme, undigested carbohydrates travel to the large intestine. Bacteria in the colon then ferment these sugars, producing gases and other byproducts that lead to gastrointestinal distress. For example, in congenital sucrase-isomaltase deficiency (CSID), undigested sucrose is fermented by gut bacteria, causing gas and watery diarrhea. A deficiency in lactase results in lactose intolerance, presenting similar symptoms upon dairy consumption. While starches have multiple enzymes for digestion, making deficiencies less pronounced, the absence of specific disaccharidases like sucrase or lactase can significantly impact digestive health. More information on CSID can be found on MedlinePlus, a resource from the National Library of Medicine.

Conclusion: The Final Breakdown

Ultimately, the question of what digestive enzyme digests sugar has a multifaceted answer. While sucrase is the specific enzyme for sucrose, a full understanding requires recognizing the coordinated effort of several enzymes. Salivary and pancreatic amylase lay the groundwork by breaking down starches, while the final, critical steps are carried out by brush border enzymes like sucrase, lactase, and maltase in the small intestine. This ensures that a variety of complex carbohydrates are converted into simple sugars, which are then absorbed to fuel the body. The health of the entire digestive system, from the mouth to the brush border, is essential for this intricate and vital process to function correctly.

Frequently Asked Questions

Amylase breaks down complex carbohydrates, specifically starches, into smaller chains and the disaccharide maltose. Sucrase, a brush border enzyme, breaks down the disaccharide sucrose (table sugar) into the simple sugars glucose and fructose.

The digestion of carbohydrates involves enzymes from several locations. Salivary amylase is in the mouth, pancreatic amylase is released into the small intestine, and specialized brush border enzymes like sucrase, lactase, and maltase are fixed on the surface of the small intestine's lining.

A deficiency in sucrase, such as with Congenital Sucrase-Isomaltase Deficiency (CSID), means sucrose cannot be properly broken down. This leads to symptoms like gas, bloating, and diarrhea when consuming foods containing sucrose.

No, humans cannot digest all types of carbohydrates. While most starches and simple sugars like sucrose and lactose are broken down by enzymes, certain fibers, such as cellulose, cannot be digested and pass through the system largely intact, providing dietary fiber.

Lactose intolerance is a specific type of sugar intolerance caused by a deficiency of the lactase enzyme, which digests milk sugar. It is different from general sugar malabsorption and does not affect the digestion of other sugars like sucrose.

Once sugars are broken down into monosaccharides (like glucose), they are absorbed into the bloodstream. From there, they are transported to cells to be used for immediate energy or sent to the liver to be stored as glycogen for later use.

Enzyme replacement therapy is available for specific diagnosed conditions like CSID or lactose intolerance. Over-the-counter supplements for general digestive issues may have limited or unproven effectiveness, and it is best to consult a doctor before using them.