What do lactase and maltase break down?

November 17, 2025 •

3 min read

Over 70% of the world's population experiences some form of lactase decline after infancy, demonstrating the critical nature of these digestive enzymes. This process involves specialized enzymes in the small intestine, but what do lactase and maltase break down specifically and how does it happen? This article delves into the roles of these vital enzymes and their respective substrates.

Quick Summary

This guide explains the specific roles of the enzymes lactase and maltase in breaking down disaccharides. It details how lactase hydrolyzes lactose into glucose and galactose, while maltase breaks down maltose into two glucose molecules. Both enzymes are crucial for carbohydrate digestion and nutrient absorption.

Key Points

Lactase breaks down lactose: This enzyme digests the milk sugar lactose into its simpler forms, glucose and galactose.
Maltase breaks down maltose: This enzyme digests maltose, a sugar derived from starch, into two glucose molecules.
Disaccharidases are key: Both lactase and maltase are disaccharidase enzymes, crucial for the final stages of carbohydrate digestion in the small intestine.
The brush border is their home: These enzymes perform their work in the brush border of the small intestine, the surface of the intestinal cells responsible for nutrient absorption.
Deficiency causes symptoms: A lack of lactase leads to lactose intolerance symptoms like bloating and diarrhea.
Incomplete digestion: Without these enzymes, disaccharides pass undigested into the large intestine, where bacterial fermentation can cause digestive distress.
Conversion to monosaccharides: The end products of this enzymatic action are monosaccharides (single sugars) that the body can directly absorb into the bloodstream for energy.

The Core Function of Digestive Enzymes

Digestive enzymes are biological catalysts that speed up chemical reactions in the body. In the context of carbohydrate digestion, enzymes known as disaccharidases are responsible for breaking down complex sugars (disaccharides) into simple, single sugars (monosaccharides) that the body can easily absorb. Lactase and maltase are two of the most important disaccharidases, operating in the brush border of the small intestine to complete the final stages of carbohydrate digestion.

Lactase: Breaking Down Milk Sugar

Lactase, also known as lactase-phlorizin hydrolase, is the enzyme responsible for digesting the milk sugar lactose.

The Substrate: The target for lactase is lactose, a disaccharide found naturally in milk and most dairy products.
The Breakdown: Lactase catalyzes the hydrolysis of lactose into two smaller, absorbable monosaccharides: glucose and galactose.
The Location: This enzymatic activity occurs in the brush border of the small intestine.
The Consequence of Deficiency: When a person lacks sufficient lactase, undigested lactose travels to the large intestine. Here, bacteria ferment the lactose, producing gas and causing uncomfortable digestive symptoms such as bloating, diarrhea, and abdominal pain—a condition known as lactose intolerance.

Maltase: Processing Malt Sugar

Maltase is another crucial disaccharidase, working alongside lactase and sucrase. It is produced by cells lining the mucous membrane of the intestinal wall.

The Substrate: Maltase's primary target is maltose, a disaccharide that results from the partial breakdown of starches by other enzymes like amylase.
The Breakdown: Maltase hydrolyzes maltose into two molecules of glucose.
The Location: Similar to lactase, maltase performs its function at the brush border of the small intestine.
The Importance: The breakdown of maltose is a final and critical step in converting complex carbohydrates into a usable energy source for the body.

Where Digestion Happens: The Brush Border

The brush border is the name for the surface of the cells lining the small intestine, which are covered in tiny projections called microvilli. This is where enzymes like lactase and maltase are embedded and perform their final digestive tasks. The proximity of these enzymes to the absorptive cells ensures that as soon as the disaccharides are broken down into monosaccharides, the body can absorb them efficiently into the bloodstream.

Lactase vs. Maltase: A Comparison

To better understand the distinct roles of these enzymes, a comparison can be helpful.


Feature	Lactase	Maltase
Substrate	Lactose (milk sugar)	Maltose (malt sugar)
Breakdown Products	Glucose and Galactose	Two molecules of Glucose
Common Source	Dairy products (milk, yogurt)	Grains and starches (cereals, pasta)
Associated Condition	Lactose Intolerance	Malabsorption linked to overall carbohydrate issues
Location of Action	Small Intestine Brush Border	Small Intestine Brush Border

The Digestive Process and Enzyme Activity

The journey of carbohydrates through the digestive system is a multi-step process. It begins in the mouth, where salivary amylase starts breaking down starches. This process is temporarily halted in the acidic environment of the stomach. The majority of carbohydrate digestion happens in the small intestine, with the help of pancreatic amylase, which continues the breakdown of starches into smaller sugars like maltose. Finally, the brush border enzymes, including lactase and maltase, complete the process by converting the remaining disaccharides into simple sugars that can be absorbed.

For most people, this process works seamlessly. However, for those with a deficiency in one of these enzymes, digestion is incomplete, leading to adverse effects. The most well-known example is lactose intolerance, which occurs when there is a lack of lactase. Similarly, a deficiency in maltase-glucoamylase can also cause malabsorption issues, though it is less common and often managed with dietary changes.

Conclusion

In summary, lactase and maltase are specialized enzymes that play crucial and distinct roles in carbohydrate digestion. Lactase is dedicated to breaking down lactose from dairy, while maltase's primary function is to break down maltose derived from starches. Both act in the small intestine to convert their respective disaccharides into simple sugars—glucose and galactose for lactase, and glucose for maltase—which the body can then absorb for energy. Understanding these specific roles is key to comprehending the overall digestive process and the causes behind common digestive issues like lactose intolerance.

Related Resources

NIH: For more on the specifics of lactose intolerance, the National Institutes of Health provides comprehensive information on the condition and its causes. You can find detailed information on the causes, diagnosis, and management of lactose intolerance at Lactose Intolerance - StatPearls - NCBI Bookshelf.

Frequently Asked Questions

The main difference lies in their substrates: lactase breaks down lactose, the sugar found in milk, while maltase breaks down maltose, a sugar derived from starches.

Both enzymes are primarily produced by the cells that line the walls of the small intestine. Specifically, they are located in the brush border of the intestinal epithelial cells.

When lactase breaks down the disaccharide lactose, it creates the two monosaccharides: glucose and galactose.

Maltase breaks down the disaccharide maltose into two molecules of glucose, which the body then uses for energy.

Lactase deficiency, also known as lactase nonpersistence, is common because in many populations, lactase enzyme activity naturally declines after infancy as milk is no longer the primary food source. Genetic factors play a significant role.

Common symptoms include bloating, gas, abdominal pain, and diarrhea after consuming dairy products. These symptoms occur because undigested lactose ferments in the large intestine.

Yes, deficiencies can be diagnosed through various tests. For lactase deficiency, a hydrogen breath test or a lactose tolerance test can be performed. Small bowel biopsies are less common but can also provide a diagnosis.

Yes, other important disaccharidases include sucrase-isomaltase, which breaks down sucrose (table sugar) and isomaltose. A deficiency in this enzyme also leads to digestive issues.