How Are Carbohydrates Broken Down?

Plate of assorted doughnuts
Refined carbohydrates cause your blood sugar to spike and crash. (Image: Comstock/Stockbyte/Getty Images)

A powdered-sugar doughnut and a chewy, whole-grain baguette are both carbohydrates, but they are broken down differently by the body. Carbohydrates fall into three basic categories: sugars, starches and cellulose. Simple sugars, or monosaccharies -- such as might be found in your doughnut -- are digested very quickly. More complex di- and polysaccharides are broken down through a series of enzymatic reactions and take longer to digest. Cellulose, which is tough plant fiber, cannot be broken down at all and passes straight through your digestive tract.

Crunchings and Munchings

The breakdown of carbohydrates begins in the mouth, where your teeth tear, grind and mash food into bits small enough to slide down the esophagus. The mashed food is moistened by juicy saliva, which contains digestive enzymes and other chemicals. An enzyme called amylase is instrumental in the digestion of starch, which is broken down into maltose, dextrins and glucose before it leaves your mouth.

Down the Hatch

Your tongue forces food to the back of your mouth, and as you swallow, the masticated carbohydrates travel through the esophagus to the stomach. The muscular walls churn food together with strong acids that assist in the breakdown of food. The acids are not specific to carbohydrates, so they function in the same way for all macronutrients.

Into the Intestines

Most of the digestive action for carbohydrates happens in the small intestines. Any starches still intact are broken down by more of the amylase enzyme. Maltose, one of the products of starch digestion, is reduced to even smaller pieces called maltase. Sucrose and lactose -- table sugar and milk sugar, respectively -- are digested by sucrase and lactase enzymes. Once di- and polysaccharides have become simple sugar units -- glucose, fructose and galactose -- they are absorbed into the blood stream. The uptake of monosaccharides is regulated by hormones, including insulin, glucagon and epinephrine, which keep your blood sugar stable.

Life Beyond Digestion

Once simple sugars enter your bloodstream, they are transported elsewhere in your body and become part of metabolic processes. For example, your body is completely dependent on the breakdown of glucose -- through processes called glycolysis and the Krebs cycle -- for energy. The main product of glucose metabolism is adenosine triphosphate, or ATP, which is the energy currency of every cell in your body.

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