Carbohydrates

Carbohydrates are organic compounds made up of carbon (C), hydrogen (H), and oxygen (O), generally in the ratio 1:2:1, (CH₂O)_n. This ratio itself gives you a hint that carbohydrates are closely related to water chemistry (H₂O pattern), which is why they are often easily metabolised.

They are also called saccharides (from the Greek word sakcharon, meaning sugar).

Now, instead of memorising definitions, think of carbohydrates as the body’s primary fuel system. Just like petrol powers a car, carbohydrates power your body.

But their role is not limited to energy—they also contribute to structure, storage, and communication at the cellular level.

Sources of Carbohydrates

Carbohydrates are widely available in our daily diet:

• Grains: Whole grains (brown rice, oats) and refined grains (white rice, flour)
• Fruits: Both fresh and dried (natural sugars)
• Vegetables: Especially starchy ones like potatoes and corn
• Dairy products: Milk and yoghurt (contain lactose)
• Legumes: Beans, lentils
• Sugary foods: Honey, sugar, soft drinks

So practically, carbohydrates are everywhere in our food system, making them the most accessible source of energy.

Classification of Carbohydrates

Now comes the most important conceptual part. Carbohydrates are classified based on the number of sugar units they contain.

1. Monosaccharides (Simple Sugars)

These are the simplest units, consisting of a single sugar molecule. They cannot be broken down further by hydrolysis. Think of them as individual bricks.

Key features → Water-soluble, Sweet in taste, Provide instant energy

Examples:

• Glucose → Primary energy currency of the body
• Fructose → Sweetest natural sugar (found in fruits)
• Galactose → Present in milk
• Ribose → Component of RNA
• Glyceraldehyde → Intermediate in metabolism

So, whenever your body needs quick energy, it relies on monosaccharides.

2. Disaccharides (Double Sugars)

These are formed when two monosaccharides join together via a glycosidic bond. Think of them as two bricks joined together.

Examples:

• Sucrose = Glucose + Fructose (table sugar)
• Lactose = Glucose + Galactose (milk sugar)
• Maltose = Glucose + Glucose

They are still sweet and energy-rich but need slight digestion before use.

3. Polysaccharides (Complex Carbohydrates)

These are long chains of monosaccharides linked together. Now imagine a full wall made of bricks—that’s a polysaccharide.

Key characteristics:

• May be soluble or insoluble
• Not sweet in taste
• Provide long-term energy storage or structural support

Examples:

• Starch → Energy storage in plants
• Glycogen → Energy storage in animals (liver and muscles)
• Cellulose → Structural component of plant cell walls
• Chitin → Found in fungal walls and insect exoskeletons
• Inulin → A prebiotic supporting gut bacteria

An important fact:
Cellulose is the most abundant biopolymer on Earth, followed by chitin.

Functions of Carbohydrates

Now let us connect structure to function—this is crucial for understanding.

Function	Explanation
Primary Source of Energy	Carbohydrates are the body’s main energy source. Glucose, derived from carbohydrate digestion, is utilised by cells through cellular respiration to produce ATP (energy).
Energy Storage	Excess glucose is stored as glycogen in the liver and muscles. When energy is required, glycogen is broken down to release glucose.
Structural Component	Carbohydrates form structural elements in organisms, such as cellulose in plant cell walls and chitin in insect exoskeletons.
Regulation of Protein and Fat Use	Carbohydrates spare proteins from being used as an energy source, allowing them to perform vital functions. They also prevent excessive breakdown of fats.
Facilitate Gut Health	Dietary fibre supports digestive health by promoting bowel movements and maintaining a healthy gut microbiome.
Component of Biomolecules	Carbohydrates are part of important biomolecules: (i) Nucleotides – Ribose and deoxyribose in RNA and DNA; (ii) Glycoproteins and Glycolipids – involved in cell signalling and recognition.

Dietary Fibre (Roughage)

This is a very interesting category.

Dietary fibre is a type of carbohydrate that cannot be digested by human enzymes.

Types:

• Soluble fibre → Dissolves in water
• Insoluble fibre → Does not dissolve (adds bulk)

Sources → Whole grains, Fruits and vegetables, Pulses

Now here is the key insight: Even though fibre does not provide nutrients, it is still essential because it:

• Promotes bowel movement
• Prevents constipation
• Supports beneficial gut bacteria

So, fibre is like a cleaning system for the digestive tract.