Sucrose, glucose and fructose are three types of sugar that contain the same number of calories gram for gram. Your tongue can’t quite distinguish between these sugars, but your body can tell the difference. They all provide the same amount of energy per gram, but are processed and used differently throughout the body.
What is Sucrose?
There are many different types of sugars, the most common of which is sucrose, otherwise known as table sugar, granulated sugar or just plain “sugar.” If you use sugar to bake or sweeten coffee or tea, sucrose is probably the type of sugar you are using. Scientifically speaking, sucrose is a type of carbohydrate, a disaccharide made of equal parts of two monosaccharides: glucose and fructose. Sucrose is a naturally occurring sugar found in various amounts in plants like fruits, vegetables and nuts.
What is Fructose?
Fructose is a sugar found naturally in many fruits and vegetables, and added to various beverages such as soda and fruit-flavored drinks. However, it is very different from other sugars because it has a different metabolic pathway and is not the preferred energy source for muscles or the brain. Fructose is only metabolized in the liver and relies on fructokinase to initiate metabolism. It is also more lipogenic, or fat-producing, than glucose. Unlike glucose, too, it does not cause insulin to be released or stimulate production of leptin, a key hormone for regulating energy intake and expenditure. These factors raise concerns about chronically high intakes of dietary fructose, because it appears to behave more like fat in the body than like other carbohydrates.
What is Glucose?
The most important monosaccharide is glucose, the body’s preferred energy source. Glucose is also called blood sugar, as it circulates in the blood, and relies on the enzymes glucokinase or hexokinase to initiate metabolism. Your body processes most carbohydrates you eat into glucose, either to be used immediately for energy or to be stored in muscle cells or the liver as glycogen for later use. Unlike fructose, insulin is secreted primarily in response to elevated blood concentrations of glucose, and insulin facilitates the entry of glucose into cells.
They’re Digested and Absorbed Differently
- Glucose is absorbed directly across the lining of the small intestine into your bloodstream, which delivers it to your cells. It raises blood sugar more quickly than other sugars, which stimulates the release of insulin. Insulin is needed for glucose to enter your cells. Once inside your cells, glucose is either used immediately to create energy or turned into glycogen to be stored in your muscles or liver for future use.
- Like glucose, fructose is absorbed directly into your bloodstream from the small intestine. It raises blood sugar levels more gradually than glucose and does not appear to immediately impact insulin levels.
- Since sucrose is a disaccharide, it must be broken down before your body can use it. Enzymes in your mouth partially break down sucrose into glucose and fructose. However, the majority of sugar digestion happens in the small intestine. The enzyme sucrase, which is made by the lining of your small intestine, splits sucrose into glucose and fructose.
