Welcome to the World of Macronutrients!
Hi there! Welcome to your study guide for Macronutrients. This is a big part of your AQA GCSE Food Preparation and Nutrition course, but don't worry—we’re going to break it down into bite-sized pieces.
Think of your body like a high-performance car. To keep it running, growing, and looking good, you need the right fuel. In nutrition, we call the "big" fuels macronutrients. There are three main ones you need to know: Protein, Fats, and Carbohydrates. Let’s dive in!
1. Protein: The Body’s Building Blocks
Imagine you are building a house. You need bricks to build the walls and more bricks to fix any parts that break. In your body, Protein is those bricks.
What does Protein do? (Functions)
Protein is essential for three main jobs:
1. Growth: Helping you grow from a baby to an adult.
2. Repair: Fixing muscles, tissues, and skin when you get hurt.
3. Maintenance: Keeping your hair, nails, and internal organs healthy.
Note: Protein can also be used for energy, but only if your body has run out of carbohydrates and fats!
HBV vs. LBV Proteins
Proteins are made of tiny building blocks called amino acids. Some proteins have all the "essential" amino acids your body needs, and some don't.
High Biological Value (HBV): These contain all the essential amino acids.
Examples: Meat, fish, poultry, eggs, milk, cheese, and soya (one of the few plant-based HBV sources!).
Low Biological Value (LBV): These are missing one or more essential amino acids.
Examples: Beans, lentils, nuts, seeds, and cereals.
Memory Aid: Protein Complementation
Don't worry if you are a vegan or vegetarian! If you eat two LBV foods together, they "complete" each other to give you all the amino acids you need. This is called Protein Complementation.
Example: Beans (LBV) + Toast (LBV) = A complete HBV meal!
Protein Alternatives
If people don't want to eat meat, they use protein alternatives. These are often low in fat and high in protein:
• Tofu: Made from soya milk bean curd.
• TVP (Textured Vegetable Protein): Made from soya flour.
• Mycoprotein (e.g., Quorn): Made from a type of fungus.
Quick Review: Too little or too much?
Deficiency (Not enough): Children may stop growing properly, hair might thin, and you may pick up infections easily.
Excess (Too much): The liver and kidneys have to work too hard to process the extra protein, which can cause them stress.
Key Takeaway: Protein is for Growth, Repair, and Maintenance. Aim for 15% of your daily energy from protein!
2. Fats: Energy and Protection
Fats often get a bad reputation, but your body actually needs them to survive! Think of fat as your body’s energy reserve and a warm winter coat.
What do Fats do? (Functions)
• Energy: Provides a concentrated source of energy.
• Insulation: A layer of fat under the skin keeps us warm.
• Protection: It acts like "bubble wrap" around your vital organs (like your kidneys) to protect them from bumps.
• Vitamins: You need fat to absorb Vitamins A, D, E, and K.
Types of Fat
Saturated Fats: Usually solid at room temperature. Too much can lead to heart disease.
Examples: Butter, lard, suet, and the fat on meat.
Unsaturated Fats: Usually liquid at room temperature and generally "healthier."
• Monounsaturated: Found in olive oil, avocados, and peanuts.
• Polyunsaturated: Found in sunflower oil and oily fish.
Common Mistake to Avoid
Don't think all fats are bad! We just need to swap saturated fats for unsaturated ones where possible. For example, use olive oil instead of butter when cooking.
Quick Review: Too little or too much?
Deficiency: If you don't have enough fat, you might feel the cold more and lose weight too quickly.
Excess: Fat is high in energy. If we don't "burn it off" through exercise, it is stored as body fat, which can lead to obesity and Type 2 diabetes.
Key Takeaway: Fats provide energy and protection. They should make up 35% or less of your daily energy intake.
3. Carbohydrates: The Body's Battery
Carbohydrates are your body's main source of energy. If you were a phone, "carbs" would be your battery charge!
Types of Carbohydrates
1. Starch (Complex Carbs): These give slow-release energy that lasts a long time.
Examples: Potatoes, bread, pasta, rice, and cereals.
2. Sugars (Simple Carbs): These give a quick burst of energy but don't last long.
• Intrinsic Sugars: Found naturally inside fruit and milk.
• Free Sugars: Added to food (like cakes, sweets, and fizzy drinks). These are the ones we should eat less of!
3. Dietary Fibre: Technically a carb, but we don't digest it for energy. It acts like a broom, sweeping your digestive system to keep it healthy and prevent constipation.
Did you know?
If you eat too many "Free Sugars," they can cause tooth decay because the bacteria in your mouth turn the sugar into acid, which eats your tooth enamel!
Quick Review: Too little or too much?
Deficiency: You will feel tired, lack energy, and may get headaches.
Excess: Extra carbohydrates are stored as fat in the body. This can lead to obesity.
Key Takeaway: Carbohydrates should provide 50% of your daily energy. Most of this should come from starch and only a tiny amount (max 5%) from free sugars.
4. Energy Needs: BMR and PAL
Everyone needs a different amount of energy. To understand why, we look at two things: BMR and PAL.
1. Basal Metabolic Rate (BMR)
This is the amount of energy your body needs just to stay alive (keeping your heart beating and lungs breathing) while you are resting.
Things that affect BMR:
• Age: Children and teenagers have a higher BMR because they are growing.
• Gender: Men usually have a higher BMR because they tend to have more muscle.
• Health: Being ill can change your BMR.
2. Physical Activity Level (PAL)
This is the energy you use for movement, like walking to school, dancing, or playing football.
The Energy Equation
To find out how much energy someone needs in total, we use this simple formula:
\( \text{Total Energy Requirement} = \text{BMR} \times \text{PAL} \)
Analogy: Think of a car. When the engine is "idling" (staying still), it uses a little fuel—that’s your BMR. When you drive the car fast, it uses much more fuel—that's your PAL!
Energy Balance
• Energy In = Energy Out: Your weight stays the same.
• Energy In > Energy Out: You gain weight (stored as fat).
• Energy In < Energy Out: You lose weight.
Key Takeaway: To maintain a healthy weight, you must balance the calories you eat with the energy you use through your BMR and PAL.