Carbohydrate digestion happens in your digestive tract. You start to break down some carbs in your mouth, but since your stomach pays more attention to proteins and fats, most carbohydrate digestion takes place in your small intestine. Once the carbs are digested into single sugar units, your body absorbs them to use as energy.
Carbohydrates include starches and sugars. Starches, or complex carbohydrates, are large molecules made up of many individual sugar units called glucose. Sugars are much smaller, made up of only one or two sugar units and can include glucose, fructose or galactose. Your body can only use individual sugar units, so anything larger needs to be digested. Once digested, the sugars are absorbed and used for energy, or when you eat too much, converted and stored as fat.
Salivary glands produce saliva as soon as you smell, or just think about, a piece of apple pie or some other delicious goodie. Saliva contains a substance called salivary amylase, which is an enzyme that breaks large starch molecules into smaller pieces. As you chew your food, the salivary amylase comes into direct contact with the starches and starts to work its chemical magic; but it doesn't last long, because when you swallow your food stomach acid stops salivary amylase in its tracks.
Your stomach doesn't do much for carbs, so they have to wait until the stomach contents are released into the duodenum, which is the first part of the small intestine. The pancreas makes another enzyme, similar to salivary amylase, but this one is called pancreatic amylase. It goes back to work on those starchy carbs, breaking them down into tiny bits of glucose, which can be absorbed through the intestinal walls and into your bloodstream.
Smaller sugars, such as sucrose, which is what we usually think of as table sugar; lactose, which is milk sugar; and maltose, which is found in beer, don't get any digestive attention until they get close to the walls of the small intestine. At this point, cells located in the walls of the small intestine make enzymes that work on each type of sugar; lactase breaks down lactose into glucose and galactose, maltase breaks down maltose into bits of glucose and sucrase breaks down sucrose into glucose and fructose. Once digested, these sugars are ready to be absorbed.
- Advanced Nutrition and Human Metabolism, 6th Edition; Sareen Gropper and Jack Smith
- KidsHealth.org: Digestive System
Sheri Kay has a master's degree in human nutrition. She's the co-author of two books and has been a nutrition and fitness writer since 2004.