Carbohydrate Digestion: Absorption, Enzymes, Process, And More

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Nutrition

How Are Carbohydrates Digested?

Medically reviewed by Katherine Marengo LDN, R.D. — Written by Ashley Marcin — Updated on June 28, 2019

Digestion process
Conditions affecting digestion
Bottom line

The body breaks simple and complex carbs into sugars and leaves fiber undigested. Some medical conditions can interrupt or affect how you digest carbs.

Carbohydrates give the body energy to go about your day’s mental and physical tasks. Digesting or metabolizing carbohydrates breaks foods down into sugars, which are also called saccharides. These molecules begin digesting in the mouth and continue through the body to be used for anything from normal cell functioning to cell growth and repair.

You’ve probably heard that some carbohydrates are considered “good” while others are “bad.” But really, it’s not so simple.

There are three main types of carbohydrates. Some carbohydrates are naturally occurring. You can find them in whole fruits and vegetables, while others are processed and refined, and either lacking in or stripped of their nutrients. Here’s the deal:

Types of carbohydrates

The three types of carbs are:

starches or complex carbs
sugars or simple carbs
fiber

Both simple and complex carbohydrates break down into glucose (aka blood sugar). A simple carb is one that’s comprised of one or two sugar molecules, while a complex carb contains three or more sugar molecules.

Fiber, on the other hand, is found in healthy carbs, but isn’t digested or broken down. It’s been shown to be good for heart health and weight management.

Naturally occurring simple sugars are found in fruit and dairy. There are also processed and refined simple sugars that food companies may add to foods such as sodas, candy, and desserts.

Good sources of complex carbohydrates include:

whole grains
legumes
beans
lentils
peas
potatoes

Fiber is found in many healthy carbs such as:

fruits
vegetables
whole grains
beans
legumes

Consuming fibrous, complex and simple carbs from naturally occurring sources like fruit may protect you from disease and may even help you maintain your weight. These carbs include more vitamins and minerals.

However, processed and refined carbohydrates are high in calories but relatively void of nutrition. They tend to make people gain weight and may even contribute to the development of obesity-related conditions, like type 2 diabetes and heart disease.

Daily intake

Carbohydrates should make up 45 to 65 percent of your daily calorie intake according to American dietary guidelines.

For a person eating a standard 2,000 calories a day, this means that carbohydrates might make up 900 to 1,300 of those calories. This figures out to around 225 to 325 grams each day. However, your carb intake will vary based on your individual needs.

How are carbohydrates digested?

All the food you eat goes through your digestive system so it can be broken down and used by the body. Carbohydrates take a journey starting with the intake at the mouth and ending with elimination from your colon. There’s a lot that happens between the point of entry and exit.

1. The mouth

You begin to digest carbohydrates the minute the food hits your mouth. The saliva secreted from your salivary glands moistens food as it’s chewed.

Saliva releases an enzyme called amylase, which begins the breakdown process of the sugars in the carbohydrates you’re eating.

2. The stomach

From there, you swallow the food now that it’s chewed into smaller pieces. The carbohydrates travel through your esophagus to your stomach. At this stage, the food is referred to as chyme.

Your stomach makes acid to kill bacteria in the chyme before it makes its next step in the digestion journey.

3. The small intestine, pancreas, and liver

The chyme then goes from the stomach into the first part of the small intestine, called the duodenum. This causes the pancreas to release pancreatic amylase. This enzyme breaks down the chyme into dextrin and maltose.

From there, the wall of the small intestine begins to make lactase, sucrase, and maltase. These enzymes break down the sugars even further into monosaccharides or single sugars.

These sugars are the ones that are finally absorbed into the small intestine. Once they’re absorbed, they’re processed even more by the liver and stored as glycogen. Other glucose is moved through the body by the bloodstream.

The hormone insulin is released from the pancreas and allows the glucose to be used as energy.

4. Colon

Anything that’s left over after these digestive processes goes to the colon. It’s then broken down by intestinal bacteria. Fiber is contained in many carbohydrates and cannot be digested by the body. It reaches the colon and is then eliminated with your stools.

Medical conditions that affect how carbohydrates are digested

There are some medical conditions that may interrupt the process of digesting carbohydrates. The following list is not exhaustive and these conditions are usually rare and genetic, meaning they’re inherited at birth.

Galactosemia

Galactosemia is a genetic disorder that affects how the body processes the simple sugar galactose, a sugar that is part of a larger sugar called lactose that’s found in milk, cheese, and other dairy products. It leads to having too much of this sugar in the blood, causing complications like liver damage, learning disabilities, or reproductive issues.

Fructose malabsorption

This condition has also been called dietary fructose intolerance. It affects how the body breaks down the sugar fructose from fruits and vegetables, honey, agave, and processed foods. Symptoms include:

nausea
diarrhea
chronic fatigue

Mucopolysaccharidoses

Hunter syndrome is a type of inherited disorder classified under mucopolysaccharidoses (MPSs). It typically begins between the ages of 2 and 4 years old and is caused by a missing enzyme that doesn’t break down carbohydrates. Physical abilities, appearance, mental development, and organ function may all be impacted by this disorder.

Pyruvate metabolism disorders

Pyruvate dehydrogenase deficiency is a type of inherited disorder classified under pyruvate metabolism disorders. It causes a buildup of lactic acid in the bloodstream.

Symptoms may begin as early as infancy. They include:

lethargy
poor feeding
rapid breathing
poor muscle tone
abnormal eye movements

Symptoms can appear worse after carbohydrate-heavy meals.

The bottom line

The body needs carbohydrates to function properly. A diet rich in healthy whole foods should give you enough fuel to power through your day.

Be sure to include a hefty amount of complex carbohydrates, like fruits and vegetables — generally between 900 and 1,300 calories each day. Of course, this amount will vary based on your height, weight, and activity level. For your specific carbohydrate needs, it’s recommended you speak with a dietitian.

Other tips

Along with fruits and vegetables, fill your plate with whole grains instead of refined grains. These complex carbohydrate choices contain more fiber and key nutrients, like B vitamins.
Watch for dairy products with added sugars. Low-fat milks, cheeses, and yogurts give the body needed calcium and protein, as well as other vitamins and minerals without the caloric load.
Incorporate more beans, peas, and lentils into your day. Not only do these legumes provide you with complex carbohydrates, but they also boast impressive amounts of protein, folate, potassium, iron, and magnesium without a lot of fat.
Read your labels. Always be on the lookout for added sugars, especially in processed foods. You should aim to get fewer than 10 percent of your calories each day from added sugars or simple carbohydrates.

How we reviewed this article:

SourcesHistoryHealthline has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical journals and associations. We only use quality, credible sources to ensure content accuracy and integrity. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.

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Medically reviewed by Katherine Marengo LDN, R.D. — Written by Ashley Marcin — Updated on June 28, 2019

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