Disaccharides are a form of carbohydrate that can be found in a wide variety of the foods we eat, such as table sugar and beetroot. Disaccharides are an energy source used by the human body, but are also used by plants for a variety of different uses (including transporting nutrients around the plant).

A disaccharide can also be classified as a double sugar as it is formed by two monosaccharides (also called single sugars) to create a disaccharide. Three of the most common disaccharides we consume are sucrose, maltose and lactose. They are found in many everyday whole foods and packaged foods we purchase from supermarkets or stores. Other less common disaccharides include lactulose, trehalose, and cellobiose, which can be found in foods like raw milk, mushrooms, some seaweeds and honey. 

When we consume disaccharides our bodies break them down into single sugars. These sugars are glucose, fructose and galactose, and they are used as energy for our body. Lactose, for example, can be found in breast milk and is used as an energy source by infants. Likewise, maltose is a sweetener that’s regularly used in confectionery like chocolate or lollies.

What happens to disaccharides during the digestion process?

As disaccharides travel through the body they are broken down into simple sugars, or monosaccharides, by a process called hydrolysis. This process is facilitated by enzymes called maltases, sucrases, and lactases. 

These different enzymes help to break down different types of sugars in the body. For example, maltase breaks down maltose into glucose, sucrases help break down sucrose into glucose and fructose, and lactases break down lactose into glucose and galactose. 

Below is a diagram of the process. 

What part of the body are disaccharides processed?

When we consume carbohydrates, our body will break these down into single sugars (monosaccharides) for digestion, absorption and transportation. 

Carbohydrate digestion starts almost immediately in the mouth with salivary amylase (an enzyme) being released during the process of chewing. Minimal carbohydrate digestion happens in the stomach due to the fact that salivary amylase is sensitive to pH and thus inhibited in the acidic environment of the human stomach. Once food moves from the stomach to the small intestine, the enzymes listed above begin to break down disaccharides. This occurs in the microvillus membrane (brush border) found in the inner wall of the small intestine.

The body then starts to absorb and transport different types of sugars around the body for use as energy. This happens via a variety of transporters located in the wall of the small intestine. Glucose and galactose are transported by the SGLT-1 transporter (sodium-glucose co-transporter) and fructose is absorbed by the GLUT5 transporter.

Digestion and absorption are coupled with enzymes closely located to the appropriate transporters to enable the body to utilise single sugars (monosaccharides) as an energy source.   

References

• Clemens RA, Jones JM, Kern M, et al. (2016). Functionality of sugars in foods and health. Comprehensive Reviews in Food Science and Food Safety, 15(3): 433-470.
• Schorin MD, Sollid K, Edge MS, Bouchoux A. (2012). The science of sugars, part 1: A closer look at sugars. Nutrition Today, 47(3): 96-101. 
• Goodman BE. (2010). Insights into digestion and absorption of major nutrients in humans. Adv Physiol Educ, 34:44-53.