Carbohydrates: Definition, Classification & Function


Have you ever heard of the saying “carbs are bad for you”? Well, that’s not entirely true! 

Carbohydrates, often called carbs, are a vital macronutrient necessary for the human body to function correctly. They provide the body with energy, aid digestion, and play a crucial role in brain function. 

In this blog, we will take a closer look at carbohydrates and explore their definition, classification, and function.

What are carbohydrates?

What are carbohydrates
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Carbohydrates reign as the king of macronutrients and serve as the primary fuel for our bodies. They are the major macronutrients and primary energy sources for us. 

When we eat carbs, our body breaks them down into simple sugars for their absorption into the bloodstream. As the sugar level rises, the pancreas releases insulin hormones. Insulin helps move sugar from the blood into the cells, where the sugar is utilized as an energy source, and every gram of carbohydrate provides four calories. 

Structure of Carbohydrates

Structure of Carbohydrates
Source: Canva

Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen atoms, with the general formula (CH2O)n, where n is a whole number. Carbohydrates can range in size from small molecules containing just a few sugar units to large polymers composed of thousands of sugar units.

The basic building blocks of carbohydrates are monosaccharides, single sugar units that hydrolysis cannot break down further. Monosaccharides are classified based on the number of carbon atoms they contain. 

The most common monosaccharides are:

  • Trioses: Contain three carbon atoms, e.g., glyceraldehyde.
  • Pentoses: Contain five carbon atoms, e.g., ribose and deoxyribose (found in DNA).
  • Hexoses: Contain six carbon atoms, e.g., glucose, fructose, and galactose.
  • Monosaccharides can be linked through glycosidic bonds to form disaccharides, oligosaccharides, and polysaccharides.

Disaccharides are composed of two sugar units linked by a glycosidic bond. 

The most common disaccharides are:

  • Sucrose: Composed of glucose and fructose and commonly found in sugar cane, sugar beets, and table sugar.
  • Lactose: Composed of glucose and galactose and commonly found in milk and dairy products.
  • Maltose: Composed of two glucose units and commonly found in germinating grains.

Oligosaccharides are composed of three to ten sugar units linked together. Examples of oligosaccharides include raffinose and stachyose in beans, lentils, and cruciferous vegetables.

Polysaccharides are composed of hundreds or even thousands of sugar units linked together. The most common polysaccharides are:

Starch: Found in plants and composed of glucose units linked together. Starch can be divided into two types: amylose, which is a straight chain of glucose units, and amylopectin, which is a branched chain of glucose units.

Glycogen: Found in animals and composed of glucose units linked together. Glycogen is stored in the liver and muscles and serves as a source of energy for the body.

Cellulose: It is found in plant cell walls and is composed of linked glucose units. Cellulose is indigestible by humans and serves as dietary fiber.

Classification of carbohydrates

Classification of carbohydrates
Source: Canva

Carbohydrates are classified into two categories:

  • Simple carbohydrates
  • Complex carbohydrates

1. Simple carbohydrates: Simple sugars are carbohydrates composed of one or two sugar molecules, making them a rapid energy source. Common examples of simple carbohydrate-rich foods include table sugar, refined grains, and candies. 

Simple carbohydrates are categorized into two types.

Monosaccharides: These refer to single sugar units such as glucose, galactose (found in milk), and fructose (found in fruits). 

Disaccharides: These are composed of two sugar molecules, such as lactose (glucose + galactose) present in milk and sucrose or table sugar (glucose + fructose).

2. Complex carbohydrates: Complex carbohydrates are composed of long chains of sugar molecules commonly found in whole grains and fruits containing dietary fiber.

Polysaccharides: These carbohydrates contain hundreds or even thousands of sugar molecules linked together, and they function as food stores for plants and animals. Examples of polysaccharides include glycogen, as well as starches that are found in potatoes, rice, and wheat.

Simple carbohydrates provide a quick energy source but tend to leave a person feeling hungry again soon after consumption. 

In contrast, complex carbohydrates tend to keep people fuller for longer periods and provide more significant health benefits than simple carbohydrates.

Carbohydrates are mainly present in three forms:

1. Starch

Starches in foods such as root vegetables, legumes, and grains consist of multiple glucose units linked together. 

Although most starches are broken down into sugars by digestive enzymes, certain types of starch are resistant to these enzymes and are not digested in the small intestine. Instead, they undergo fermentation by bacteria in the large intestine, producing short-chain fatty acids and serving as dietary fiber.

2. Sugar

Sugary foods can provide a rapid energy source for the body because they are quickly broken down into simple sugars. However, this can cause a rapid rise in blood sugar levels, followed by a rapid drop.

Types of sugar:

  • Naturally occurring sugars, for example, milk sugar.
  • Added sugars are added to processed foods like sweets, candies, canned fruits, and desserts. Excess intake of such foods might result in obesity, type 2 diabetes, heart disease, and inflammation.

3. Dietary Fiber

Dietary fiber, also known as roughage, refers to the indigestible parts of plant-based foods, such as cellulose, hemicellulose, gums, and mucilages. Consuming a diet rich in fiber, including foods such as nuts, seeds, cereals, fruits, and vegetables, can positively impact overall health by reducing the incidence of various diseases. 

Consuming between 25-40 grams of dietary fiber per day is recommended, incorporating both 

Types of fiber in the diet.

Soluble dietary fiber- It is a type of fiber that dissolves in water to form a gel-like substance in the digestive tract. It can help lower blood cholesterol and glucose levels and promote healthy bowel movements.

Food sources rich in soluble fiber include oats, peas, beans, apples, citrus fruits, carrots, barley, and psyllium. Incorporating these foods into your diet can help support overall health and wellness.

Insoluble dietary fiber- Insoluble dietary fiber is resistant to water and cannot dissolve in it. This fiber promotes a healthy digestive system by increasing stool bulk and can be especially beneficial for individuals who struggle with constipation or irregular bowel movements. 

Some good sources of insoluble fiber include whole wheat flour, wheat bran, nuts, beans, cauliflower, green beans, and potatoes. Incorporating these foods into your diet can help support healthy digestion and bowel movements.

According to the Indian Council of Medical Research (ICMR) dietary guidelines, a balanced diet for Indians should include healthy sources of carbohydrates that provide 50-60% of daily calories. However, individual requirements may vary depending on factors such as age, gender, activity level, and overall health status. It is essential to consult with a healthcare professional or registered dietitian to determine the optimal carbohydrate intake for your individual needs.

Functions of Carbohydrates

Functions of Carbohydrates
Source: Canva

The functions of carbohydrates are:

1. Energy-giving

Carbohydrates are the nutrients that provide energy for the body, enabling us to carry out physical activities such as walking and even breathing. These nutrients are also vital for fueling the brain and energizing us.

2. Mood uplifter

According to certain studies, carbohydrates have been shown to facilitate the production of serotonin, a neurotransmitter associated with positive emotions. When serotonin levels are too low, it can lead to depression and other mental health issues.

3. Support muscle building

The role of carbohydrates in providing energy is essential for supporting intense workouts and replenishing depleted glycogen stores during bodybuilding. When combined with protein, carbohydrate intake can enhance muscle protein synthesis, aiding in the growth and repair of muscle tissue.

4. Support weight loss

A diet abundant in complex carbohydrates and rich in dietary fiber can help prevent overconsumption of calories, increase metabolism, and encourage body fat loss.

5. Promote digestive health

Consuming sufficient dietary fiber is crucial for maintaining a healthy gut, promoting efficient waste removal, and preventing constipation and other digestive problems.

6. Lowered Risk of Chronic Diseases

A diet rich in whole grains, fruits, and vegetables, which are sources of complex carbohydrates, can lower the risk of chronic diseases such as heart disease, type 2 diabetes, and some types of cancer.

7. Improved Athletic Performance

Consuming carbohydrates before and after exercise can improve athletic performance by providing energy for physical activity and promoting muscle recovery.

List of Carbohydrate-rich foods

List of Carbohydrate-rich foods
Source: Canva

Many healthy food options are rich in carbohydrates. Here are some examples:

Whole grains: Whole wheat bread, brown rice, quinoa, oats, and barley are all great sources of complex carbohydrates.

Fruits: Fruits like bananas, apples, oranges, berries, and melons are all good sources of carbohydrates, as well as fiber, and essential vitamins and minerals.

Vegetables: Starchy vegetables like sweet potatoes, potatoes, corn, peas, and squash are all good sources of carbohydrates, as well as non-starchy vegetables like broccoli, spinach, and green beans.

Legumes: Lentils, chickpeas, black beans, and kidney beans are all high in carbohydrates and protein, making them a great addition to a healthy diet.

Dairy products: Milk, yogurt, and cheese contain carbohydrates in the form of lactose, as well as essential nutrients like calcium.

It’s important to choose whole, unprocessed foods as much as possible and to balance your carbohydrate intake with protein, healthy fats, and fiber to support overall health and wellness.

Impact of different types of carbohydrates on health

Impact of different types of carbohydrates on health
Source: Canva

The type and amount of carbohydrates consumed can significantly impact health. Here are some examples:

Simple Carbohydrates: Consuming large amounts of simple carbohydrates, especially added sugars, has been linked to an increased risk of obesity, type 2 diabetes, and heart disease. Simple carbohydrates can cause rapid spikes and drops in blood sugar levels, leading to feelings of hunger and fatigue.

Complex Carbohydrates: Consuming complex carbohydrates, significantly high in fiber, can help promote weight loss, lower cholesterol levels, and reduce the risk of chronic diseases like type 2 diabetes and heart disease. Complex carbohydrates provide a sustained release of energy, keeping you feeling fuller for more extended periods.

Fiber: Consuming adequate amounts of fiber, both soluble and insoluble, can help promote healthy digestion, regulate blood sugar levels, and reduce the risk of chronic diseases like colon cancer and heart disease.

Resistant Starch: Consuming resistant starch can also have health benefits, such as promoting healthy digestion and reducing the risk of chronic diseases like type 2 diabetes and colon cancer.


Carbohydrates: Definition, Classification & Function
Source: Canva

To conclude, consuming a well-balanced diet that includes unprocessed and unrefined carbohydrates, vitamins and minerals, adequate sleep, and physical activity is associated with good health and healthy body weight. Before buying any packaged food, make it a habit to read nutrition facts and labels. 

What are the classification of carbohydrates and its function?

How are carbohydrates classified? Carbohydrates are divided into four types: monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Monosaccharides consist of a simple sugar; that is, they have the chemical formula C6H12O6. Disaccharides are two simple sugars.

What are the 3 classification of carbohydrates define each?

They are mainly classified into three groups: MonosaccharidesDisaccharidesPolysaccharides.

What are the 5 classifications of carbohydrates?

They are normally broken down into five major classifications of carbohydrates:

What are carbohydrates give its classification chart?

Classification of carbohydrates: Carbohydrates are classified into three broad groups in accordance with their behaviour on hydrolysis as monosaccharides, oligosaccharides, and polysaccharides.

What is the main role of carbohydrates in the body?

Carbohydrates are your body’s main source of energy: They help fuel your brain, kidneys, heart muscles, and central nervous system. For instance, fiber is a carbohydrate that aids in digestion, helps you feel full, and keeps blood cholesterol levels in check.

Who discovered carbohydrates?

Introduction. That ‘carbohydrates’ played an important role in diabetes was known to the Indian physician Sushruta who, identified it in the sixth century BCE as madhu-meha or sweet-urine, made the connection with rice (grain) and prescribed a reduced intake and an increase in exercise.

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