The Digestion & Absorption of Sucrose

Sucrose is a disaccharide, or two-unit carbohydrate, linking glucose and fructose molecules. You may know it as table sugar, since most table sugar comes from sugar cane or sugar beets, and both sources are among the richest in sucrose. However, all fruits and vegetables contain some sucrose, as it is the main product of photosynthesis, the process that all plants use to convert the sun's energy into food. Your body primarily digests and absorbs sucrose for energy production.

Sucrose Digestion

As a disaccharide, sucrose is too large to cross cell membranes. As a result, your body must first break it down through enzymatic digestion before it can absorb it. Sucrose digestion begins in your small intestine with a process called hydrolysis. In this chemical process, a water molecule helps to break the bond between glucose and fructose with the assistance of sucrase. Sucrase is an enzyme of the small intestine that your body needs to digest sucrose because it specifically cleaves the type of glucose-fructose bond that occurs in sucrose.

Sucrose Absorption

The Digestion & Absorption of Sucrose

Learn More

Once your body has broken sucrose down, it can absorb its individual sugars, glucose and fructose. With the help of complex transport molecules, the glucose and fructose in your gut must first enter the cells that line your small bowel, then cross them to get into your bloodstream. Glucose absorption into your bowel's lining requires a transporter called SGLUT1, while GLUT5 transports fructose. Note that SGLUT1 only carries glucose if sodium is available alongside it. Then, GLUT2 transporters carry both glucose and fructose into your bloodstream. Like a highway, your blood provides a platform for nutrients to travel to different organs.

Metabolism

Glucose and fructose differ in important ways in their metabolism. Glucose is your body's preferred energy source. As it enters your bloodstream and blood levels rise, the insulin hormone sends signals to your cells to pick it up. All tissues have the chemical machinery to break down glucose and use it for energy production. In contrast, fructose does not trigger insulin response and few tissues can process it. Biochemist Pamela Champe, Ph.D., notes that your liver must first process fructose before it can enter metabolic pathways leading to energy production. To a lesser extent, your kidneys can also metabolize fructose.

Storage

Is Glucose Stored in the Human Body?

Learn More

Your body stores most of the excess glucose in the form of glycogen, via a process called glycogenesis. Glycogenesis joins single molecules of glucose to form longer chains of glucose. These long chains are the glycogen that your muscles and liver store for later energy needs. Whenever your blood sugar drops and you are not eating, your body can break glycogen down and release individual glucose units for energy. Thus, organs that require a steady glucose supply to function properly can continue to receive it. Once glycogen stores are full, your system converts the remaining glucose into fat. Concerning excess fructose, your liver primarily converts it into glycerol, the building block of blood fats.

Malabsorption

The digestion and absorption of sucrose is so efficient that, according to Champe, a healthy person absorbs all digested sucrose before the ingested food reaches the lower bowel. In some people, however, enzyme deficiencies can inhibit or limit the process. Sucrase deficiency, for instance, is a genetic disorder that reduces or prevents the production of sucrase, thus blocking sucrose digestion and absorption. As a result, sucrose goes through your bowel undigested and becomes a food source for bacteria. The bacterial metabolism of sucrose can cause abdominal cramping, bloating, constipation and diarrhea. Sucrose malabsorption reduces your body’s ability to produce energy, potentially affecting your overall metabolism.