How Are Carbohydrates Digested, Absorbed & Eliminated?

Carbohydrates, one of the four major macronutrients, provide a significant amount of fuel to the human body. However, if carbohydrates are not prop

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Carbohydrates, one of the four major macronutrients, provide a significant amount of fuel to the human body. However, if carbohydrates are not properly digested and absorbed, they cannot perform their essential functions. Digestion and absorption occurs along the gastrointestinal tract, and remaining, undigested carbohydrates are then eliminated from the colon.

Types of Carbohydrates

There are three main types of carbohydrates: starches, sugars and dietary fiber. Starches and sugars are considered the energy-yielding carbohydrates because they are fully digestible and, once absorbed, they provide the body with 4 calories of energy per gram of carbohydrate. Alternatively, fiber is a type of carbohydrate which is not fully digestible because humans lack the enzymes to break down fibers. As such, fiber is the main carbohydrate which is eliminated through excretion.

Carbohdyrate Digestion

The two digestible carbohydrates are starches and sugars, and both of these carbohydrates are digested, or broken down into their most elementary form, along the gastrointestinal tract. Amylase, an enzyme which breaks apart starches, is found in the mouth and in the small intestine. Similarly, the three major enzymes which break apart sugars — sucrase, maltase and lactase — are also found in the mouth and in the small intestine. Once these digested starches and sugars begin to move through the small intestine, they are able to be absorbed.

Carbohydrate Absorption

Once carbohydrates are broken down into their simplest forms, they are quickly absorbed along the upper and lower parts of the small intestine. Small, finger-like projections, called villi, absorb the carbohydrates, then they are transferred to the blood stream and carried to muscles and the liver.

Carbohydrate Elimination

When carbohydrates are not fully digested or absorbed, they are eliminated from the body. Dietary fiber is one of the carbohydrates which humans cannot digest, thus dietary fiber is the most commonly excreted type of carbohydrate. In addition, lactose, a type of sugar, can also be excreted if an individual lacks the proper enzymes to digest this carbohydrate. All undigested carbohydrates move from the small intestine, where absorption would normally occur, to the large intestine and the colon, where elimination finally occurs.

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