Carbohydrates: Definition, Classification & Function


Carbohydrates are organic compounds that contain carbon, hydrogen, and oxygen.

The three major sources of carbohydrates in the human diet are sugars, starches, and cellulose.

Carbohydrates are an important source of energy for the body.

Carbohydrates can be classified by their chemical structures as either simple or complex.

What are carbohydrates?

Carbohydrates 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 in the body, the pancreas releases insulin hormone. Insulin helps move sugar from the blood into the cells, where the sugar is utilized as an energy source. Every gram of carbohydrate provides four calories. 

Classification of carbohydrates

Carbohydrates are classified as simple and complex.

1. Simple carbohydrates: These are sugars containing one or two sugar molecules, due to which simple sugars act as an instant energy source. Table sugar, candies and refined grains are examples of simple carbohydrate food. Simple carbohydrates are further of two types:

  • Monosaccharides: Contains single sugar units like glucose, galactose (present in milk) and fructose (present in fruits).
  • Disaccharides: Contain two sugar molecules like lactose present in milk (glucose+galactose) and sucrose or table sugar (glucose + fructose).

2. Complex carbohydrates: Consist of long chains of sugar molecules and are present in fruits and whole grains containing dietary fibre. 

  • Polysaccharides: Consist of hundreds or thousands of sugar molecules and act as food stores for plants and animals. Examples include glycogen, starches present in potatoes, rice, and wheat.

Simple carbohydrates provide a rapid energy source, but the person soon feels hungry again. Complex carbohydrates keep us full for longer and have more health benefits than simple carbs.

Carbohydrates are mainly present in three forms in our food.

  1. Starch
  2. Sugar
  3. Dietary Fibre


Starches include multiple glucose units attached to each other. They are found in many foods, including root vegetables, legumes, and grains. Most starches are broken down to sugars by digestive enzymes, but some are resistant to digestive enzymes and do not get digested in the small intestine. Instead, it gets fermented by the bacteria present in the large intestine producing short fatty acids and becoming a form of fibre.


Sugary foods are a quick energy source as our body breaks down simple sugars quickly. As a result, blood sugar levels rise and then drop rapidly. 

Types of sugar:

  • Naturally occurring sugars, for example, milk sugar.
  • Added sugars 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.

Dietary Fibre

Dietary fibre or roughage is an indigestible part of plant foods, for example, cellulose, hemicellulose, gums and mucilages. Diets rich in fibre such as nuts, seeds, cereals, fruits and vegetables have a favourable effect on health because their consumption decreases the incidence of several diseases. Our diets must include 25-40 g of dietary fibre per day, combining both types.

  • Soluble Dietary Fibre: This type dissolves in water to form a gel-like substance. It can assist in lowering blood cholesterol and glucose levels. Food sources include oats, peas, beans, apples, citrus fruits, carrots, barley and psyllium. 
  • Insoluble Dietary Fibre: It is insoluble in water, promotes a digestive system, increases stool bulk, and benefits people who struggle with constipation or irregular bowel movements. Whole wheat flour, wheat bran, nuts, beans, cauliflower, green beans, and potatoes are good insoluble fibre sources.

As per ICMR dietary guidelines for Indians, a balanced diet must provide 50-60% of calories from healthy sources of carbohydrates. Although, the requirement may vary from person to person.

Carbohydrates Function

These are some health benefits and importance of carbohydrates:

  1. Energy-giving: We need the energy to do everything from breathing, walking, or any physical activity. Carbohydrates are the energy-giving nutrients for the body. They are fuel for our brain and keep us energetic.
  2. Mood uplifter: Some studies suggest that carbs promote the production of serotonin, a feel-good neurotransmitter. Too low levels of serotonin might result in depression and other mental illnesses. 
  3. Support muscle building: Carbohydrates play a crucial role in supplying energy to support the intense workout and restock lost glycogen stores during bodybuilding. Intake of protein with carbs amplifies muscle protein synthesis.  
  4. Support weight loss: Diet rich in complex carbs packed with dietary fibre prevents excess calorie intake, boosts metabolism, and promotes fat loss.
  5. Promote digestive health: Adequate dietary fibre keeps our gut healthy, helps effective waste removal, prevents constipation and other indigestion issues.

To conclude, consuming a well-balanced diet that includes unprocessed and unrefined carbohydrates, vitamins and minerals with 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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