Carbohydrates are the body’s main source of energy and help support brain function, muscles, and daily activities.
Simple carbohydrates are absorbed quickly and can raise blood sugar faster than complex carbohydrates.
Fiber is a type of carbohydrate that supports digestion, helps regulate blood glucose, and promotes fullness.

Carbohydrates are nutrients made of carbon, hydrogen, and oxygen. They provide energy to support vital bodily functions, such as breathing and heartbeat.

They also give the body energy for daily activities, such as working and exercising. Carbohydrates are also known as carbs, glycides, or saccharides.

Based on their structure, carbohydrates are classified as simple or complex. This affects how quickly they are absorbed by the body and how they affect blood glucose levels.

Types of carbohydrates

Carbohydrates can be classified as simple or complex, depending on their structure.

1. Simple carbohydrates

Simple carbohydrates have a simple chemical structure, which allows them to be broken down and absorbed quickly by the body.

This type of carbohydrate can be classified as:

Monosaccharides: these are the simplest units or molecules that form more complex carbohydrates when joined together. Examples of monosaccharides include glucose, ribose, xylose, galactose, and fructose.
Disaccharides: these are made up of two monosaccharide units, such as sucrose or table sugar (glucose + fructose), lactose (galactose + glucose), and maltose (glucose + glucose).
Oligosaccharides: these are made up of 3 to 10 monosaccharide units. Some may have probiotic action, such as fructooligosaccharides (FOS) and galactooligosaccharides (GOS).

Because they are digested and absorbed more easily, simple carbohydrates can cause blood sugar to rise quickly. This means they usually have a high glycemic index.

In addition, this type of carbohydrate can increase hunger and, when consumed in excess, may contribute to body fat accumulation and weight gain.

2. Complex carbohydrates

Complex carbohydrates, or polysaccharides, contain more than 10 monosaccharide units. They form complex structures that may be linear or branched.

Some examples of complex carbohydrates are starch, cellulose, and glycogen.

Complex carbohydrates include fiber, which is found in plants and is not digested by gastrointestinal enzymes. Examples include cellulose, fructooligosaccharides (FOS), and lignin, which slow digestion, promote fullness, and stimulate bowel movements.

Unlike simple carbohydrates, complex carbohydrates are digested and absorbed more slowly. This gradual release of energy helps keep blood glucose levels stable.

Carbohydrate foods

Some examples of carbohydrate-containing foods include:

Type of carbohydrate	Foods
Simple carbohydrates	White sugar, brown sugar, demerara sugar, honey, maple syrup, high-fructose corn syrup, milk, fruit, and soda
Complex carbohydrates	Rice, pasta, white bread, wheat flour, cassava, cornmeal, and potatoes
Fiber-rich complex carbohydrates	Brown rice, whole wheat pasta and bread, beans, chickpeas, lentils, fruit with peel and pulp, and raw vegetables

Other high carb foods include sweet potatoes, yams, and oats.

What do carbohydrates do?

The main functions of carbohydrates are:

1. Producing energy

Carbohydrates are the body’s main source of energy because they are broken down into glucose during digestion.

The body needs an average of 160 g of glucose to function properly, and glucose is the preferred fuel for the body’s cells.

When glucose is absorbed in the intestine, much of it is broken down to produce adenosine triphosphate (ATP). ATP is an energy molecule that is essential for several metabolic processes in the body.

2. Providing energy for the brain

Glucose produced during the digestion of simple and complex carbohydrates is used mainly by the brain to support vital functions. The brain uses around 120 g of glucose per day as its main source of energy.

3. Storing energy

Part of the glucose absorbed in the intestine is stored as glycogen in the liver.

Another portion of glucose is stored in the muscles. It can be used in situations of increased demand, such as prolonged fasting, extended high‑intensity exercise, heightened alertness, or illness.

4. Preserving muscle mass

Carbohydrates help preserve muscle because, when glucose is low, the body may start breaking down muscle tissue for energy.

This happens because muscle proteins can be broken down into amino acids, which the body can then convert into glucose.

5. Improving digestive health

Fiber is a type of carbohydrate that is not digested and does not produce glucose. However, it is essential for digestive health.

This is because fiber supports healthy gut flora, regulates blood glucose levels, and stimulates bowel movements. This can help prevent problems such as constipation, diarrhea, and diabetes.

Recommended amount

The World Health Organization (WHO) recommends that carbohydrates make up 40 to 70% of total daily calories. For example, a person who eats 1,800 calories per day should consume about 180 to 315 g of carbohydrates per day.

The daily fiber recommendation is 15 g for children 2 to 5 years old and 21 g for children 6 to 9 years old. According to the World Health Organization, adults should consume at least 25 g of naturally occurring dietary fiber per day.

How carbs are broken down

Carbohydrate metabolism involves several pathways:

Glycolysis: the breakdown of glucose to produce ATP and pyruvate, which the body uses to generate energy.
Glycogenesis: the formation and storage of glycogen in the liver and, to a lesser extent, in the muscles. This mainly occurs after eating carbohydrate-rich foods.
Gluconeogenesis: the production of glucose from non-carbohydrate sources such as glycerol, fatty acids, amino acids, or lactate. This pathway becomes more active during prolonged fasting.
Glycogenolysis: the breakdown of glycogen stored in the liver and/or muscles to release glucose, especially when the body needs to raise blood sugar levels.

These pathways are activated as needed, depending on the body’s energy demands and nutritional state.

What are Carbohydrates? Types, Foods & Amounts