Sign up to access the complete lesson and track your progress!
Unlock This CourseEvery day, your body needs fuel to keep you going - just like a car needs petrol! The three main types of fuel your body uses are called macronutrients: carbohydrates, proteins and lipids (fats). These aren't just boring chemicals - they're the building blocks that keep you alive, help you grow and give you energy to play football, think in lessons and even sleep properly.
Key Definitions:
Your body is like a busy factory that never stops working. Even when you're sleeping, your heart beats, your brain thinks and your cells repair themselves. All this work needs energy, which comes from the food you eat. Without the right nutrients, you'd feel tired, get ill easily and stop growing properly.
Carbohydrates are like the petrol in your body's engine. They're made up of carbon, hydrogen and oxygen atoms and they're your body's preferred source of quick energy. When you eat a slice of toast or a banana, you're giving your body carbohydrates to burn as fuel.
Not all carbohydrates are the same - some are simple and quick to use, whilst others are complex and release energy slowly.
Examples: Glucose, fructose (fruit sugar), sucrose (table sugar). These give you quick energy but don't last long - like sprinting!
Examples: Starch in potatoes, bread and rice. These release energy slowly and steadily - like jogging for a long time.
Examples: Cellulose in vegetables and fruits. Your body can't digest this, but it helps keep your digestive system healthy.
Benedict's Test for Sugar: Add Benedict's solution to your food sample and heat it. If sugar is present, the solution changes from blue to brick-red. Iodine Test for Starch: Add iodine solution to your sample. If starch is present, it turns from brown to blue-black.
If carbohydrates are like petrol, then proteins are like the bricks and cement that build and repair your body. Every muscle, every hair on your head and even the enzymes that help you digest food are made of proteins. They're made up of smaller units called amino acids - think of them as different coloured Lego blocks that can be arranged in millions of ways.
Proteins are the ultimate multitaskers in your body. They don't just sit there - they're constantly working to keep you healthy and growing.
When you exercise and your muscles get tiny tears, proteins fix them and make them stronger. When you cut yourself, proteins help heal the wound. Growing taller? That's proteins building new cells!
Enzymes are special proteins that act like molecular scissors, cutting up your food into pieces small enough for your body to absorb. Without them, you couldn't digest anything!
In some parts of the world where people don't get enough protein, children can develop a disease called kwashiorkor. Their bellies swell up, their hair changes colour and they stop growing properly. This shows just how important protein is for normal development. The good news is that it can be treated by adding protein-rich foods to the diet.
When people hear 'fat', they often think it's bad, but lipids (the scientific name for fats and oils) are actually essential for life. They're made of carbon, hydrogen and oxygen, just like carbohydrates, but arranged differently. Think of lipids as your body's insulation, energy storage and waterproofing system all rolled into one.
Lipids come in different forms and do different jobs in your body. Some protect you, some store energy and some even help make important hormones.
Lipids store twice as much energy as carbohydrates! Your body saves them for when you really need energy, like during a long hike or when you're ill.
A layer of fat under your skin keeps you warm in winter - like wearing a built-in jumper that never comes off!
Fat cushions your vital organs like your kidneys and heart, protecting them from bumps and knocks.
To test for lipids in food, add ethanol to your sample, shake it, then add water. If lipids are present, the mixture turns cloudy white - this is called an emulsion. Try this with milk (contains fat) and water (no fat) to see the difference!
Enzymes are like incredibly efficient workers in a factory. Each enzyme has one specific job and they work at amazing speeds to break down your food. Without enzymes, it would take years to digest a single meal!
Enzymes work using something called the 'lock and key' model. Each enzyme (the lock) only fits with one specific substance (the key). When they fit together, the enzyme breaks the substance down into smaller pieces.
Amylase breaks down starch into simple sugars. You can find it in your saliva - that's why bread starts to taste sweet if you chew it for ages!
Pepsin in your stomach breaks down proteins into amino acids. It works best in acidic conditions - that's why your stomach produces acid!
Lipase breaks down lipids into fatty acids and glycerol. It's made in your pancreas and works in your small intestine.
Now you know about the three macronutrients, but how much of each do you need? It's all about balance - like making sure you have the right ingredients for a recipe.
The UK government created the Eatwell Guide to show people how to eat a balanced diet. It looks like a plate divided into sections: about a third should be fruits and vegetables, a third should be starchy carbohydrates like bread and potatoes, some protein foods like meat and beans, some dairy and just a tiny bit of foods high in fat and sugar. This ensures you get all the macronutrients you need in the right proportions.
When people don't get enough of certain macronutrients, they can develop deficiency diseases. Understanding these helps us see why balanced nutrition is so important.
Without enough carbohydrates, you feel tired and weak. Your body starts breaking down proteins for energy instead of using them for growth and repair.
Protein deficiency causes poor growth, muscle wasting and a weak immune system. Children are especially affected because they need protein to grow.
Some lipids are 'essential' - your body can't make them, so you must get them from food. Without them, your skin becomes dry and your brain doesn't work properly.