Carbohydrate (Macronutrient)

Introduction to Carbohydrates

Welcome to your study notes on Carbohydrates! In this chapter, we are going to explore one of the most important macronutrients in our diet. Think of carbohydrates as the "fuel" for your body’s engine. Just like a car can't run without petrol, your body can’t function properly without the energy that carbohydrates provide.

Don't worry if the science bits seem a little tricky at first—we will break everything down into bite-sized pieces to help you master this topic for your OCR GCSE exam!

1. What are Carbohydrates?

A macronutrient is a nutrient that the body needs in large amounts. Carbohydrates are made up of three elements: Carbon, Hydrogen, and Oxygen. Their main job is to provide us with energy.

The Two Main Groups

We generally split carbohydrates into two categories based on how "complex" their chemical structure is:

1. Sugars (Simple Carbohydrates): These are small molecules that the body can break down very quickly for a "fast" burst of energy.
2. Complex Carbohydrates (Starches and Fibre): These are much larger molecules made of long chains. They take longer to digest, giving you "slow-release" energy that lasts longer.

Quick Review: Why do we call them macronutrients? Because we need them in large quantities every day!

2. The Structure of Carbohydrates

To understand carbohydrates, it helps to imagine them as Lego bricks. Some are just one brick, and some are huge towers built of many bricks.

A. Sugars (Simple)

Sugars are divided into two types:

Monosaccharides (Single Sugars)

The word "Mono" means one. These are the simplest form of sugar. They are the building blocks for all other carbs.

• Glucose: Found in ripe fruits and vegetables. It is the form of sugar that travels in our blood.
• Fructose: Known as "fruit sugar," found naturally in honey and fruits.
• Galactose: Found in milk (it joins with glucose to make the sugar in milk).

Disaccharides (Double Sugars)

The word "Di" means two. These are formed when two monosaccharides join together.

• Sucrose: (Glucose + Fructose). This is the white "table sugar" we use in baking.
• Lactose: (Glucose + Galactose). The sugar found in milk.
• Maltose: (Glucose + Glucose). Found in cereals like barley.

Memory Aid: To remember the three Disaccharides, think of "S.L.M" — Super Lovely Meal (Sucrose, Lactose, Maltose).

B. Complex Carbohydrates (Polysaccharides)

"Poly" means many. These are made of thousands of glucose molecules joined together in long chains.

• Starch: This is how plants store energy. We find it in foods like potatoes and bread.
• Fibre (NSP): Also known as Non-Starch Polysaccharide. This is the part of the plant that our bodies cannot digest.

Key Takeaway: Simple sugars give quick energy; complex starches give slow-release energy.

3. Functions of Carbohydrates

Why do we actually need to eat these foods? Here are the three main jobs they do:

1. Energy Production: This is the primary function. Carbohydrates are the body's preferred source of energy. Every gram of carbohydrate provides: \( 16 \text{ kJ} \) (or \( 3.75 - 4 \text{ kcal} \)).

2. Protein Sparing: If we eat enough carbohydrates, our body uses them for energy first. This "spares" protein, allowing protein to do its own important job of growth and repair instead of being wasted as fuel.

3. Digestion (Fibre): Fibre (NSP) is essential because it acts like a "broom" in your digestive system. It helps move waste products through the intestines and prevents constipation.

Did you know? The government recommends that about 50% of our daily energy should come from carbohydrates!

4. Sources of Carbohydrates

You need to be able to identify which foods provide which types of carbohydrates for your exam.

Sources of Sugar

• Natural sugars: Honey, maple syrup, fruits, and milk.
• Added (Free) sugars: Sweets, fizzy drinks, cakes, and table sugar.

Sources of Starch

• Potatoes, yams, and cassava.
• Bread, pasta, rice, and couscous.
• Cereals like oats, wheat, and rye.

Sources of Fibre (NSP)

• Wholemeal bread and wholegrain pasta.
• The skins of fruits and vegetables (like potato skins).
• Pulses (beans, lentils, and chickpeas).
• Oats and bran.

Common Mistake to Avoid: Many students think "carbs" only means bread and pasta. Remember that fruit and vegetables are also excellent sources of carbohydrates (sugar and fibre)!

5. Health: Deficiency and Excess

In nutrition, balance is everything. We want to avoid having too little or too much.

What happens if we don't eat enough? (Deficiency)

If you don't eat enough carbohydrates, you might experience:

• Lack of energy/fatigue: You will feel tired and struggle to concentrate.
• Weight loss: The body will start to burn its own fat and muscle for fuel.
• Poor digestion: A lack of fibre can lead to constipation and increases the risk of diverticulitis (a condition affecting the large intestine).

What happens if we eat too much? (Excess)

If we eat more energy than we use, the body stores it for later:

• Weight gain/Obesity: Excess carbohydrates are converted into fat and stored in the body.
• Tooth Decay: High intake of free sugars (added sugars) provides food for bacteria in the mouth, leading to cavities.
• Type 2 Diabetes: A diet very high in sugar is a risk factor for developing diabetes.

Quick Review Box:
- Energy value: \( 4 \text{ kcal per gram} \)
- Deficiency: Tiredness and constipation.
- Excess: Obesity and tooth decay.

6. Working Characteristics in Food Preparation

While this chapter focuses on nutrition, it's helpful to know how carbohydrates behave when we cook them. This links to Section C of your course.

• Gelatinisation: When starch is heated in liquid (like making a white sauce), the starch granules swell and burst, thickening the liquid.
• Dextrinisation: When starch is hit with dry heat (like toasting bread), it turns brown and tastes sweeter.
• Caramelisation: When sugar is heated, it melts and turns into a brown, syrupy liquid with a distinct flavour.

Encouraging Note: You’re doing great! Carbohydrates are the foundation of a healthy diet. Just remember to choose complex carbohydrates (wholegrains) more often than simple sugars to keep your energy levels steady.

Summary: Key Takeaways

1. Carbohydrates are macronutrients required for energy and fibre.
2. Monosaccharides (Glucose, Fructose, Galactose) are the simplest building blocks.
3. Starch and Fibre are complex carbohydrates that provide slow-release energy and aid digestion.
4. Carbohydrates provide \( 16 \text{ kJ} / 4 \text{ kcal} \) per gram.
5. Excess sugar leads to obesity and tooth decay, while a lack of fibre causes constipation.