📚 IGCSE Food & Nutrition (0648) Study Notes 📚

Chapter 5: Composition and Value of the Main Foods in the Diet

Hello future food scientists! 👋 This chapter is all about getting to know the ingredients we use every day. We’ve learned about nutrients (Topic 2), and now we look at which foods actually contain them. Understanding the composition (what’s inside the food) helps us make smart choices for a healthy, balanced diet. Let's dive into the main food groups!

1. Sources of Protein: The Body's Building Blocks

Proteins are essential for growth, repair, and making hormones and enzymes. When assessing the value of a protein source, we look at its **Biological Value** (HBV or LBV – remember this from Topic 2!).

1.1 Dairy Products (Milk, Cheese, Yogurt)

Dairy foods are vital sources, especially for growing children and pregnant women.

  • Nutritive Value:
    • Protein: Excellent source of High Biological Value (HBV) protein.
    • Minerals: Very high in Calcium (essential for strong bones and teeth) and Phosphorus.
    • Vitamins: Good source of Vitamin B group (Riboflavin, Cobalamin). Full-fat milk contains Vitamins A and D.
    • Carbohydrate: Contains the sugar Lactose.
  • Did you know? Lactose intolerance occurs when the body lacks the enzyme lactase to break down lactose.

1.2 Eggs

Eggs are often considered the ‘perfect’ natural food because they contain almost every essential nutrient.

  • Nutritive Value:
    • Protein: Pure HBV protein, used very efficiently by the body.
    • Vitamins: Rich in Vitamin A, D, E, and B group (especially B12 in the yolk).
    • Minerals: A good source of Iron and Phosphorus.
    • Fats: Found mostly in the yolk.
  • Analogy: Think of an egg as a single-serving HBV protein super-source!

1.3 Fish

Fish is a highly digestible source of protein and can be categorised by its fat content:

  • White Fish (e.g., Cod, Haddock, Tilapia):
    • Very low in fat and calories.
    • HBV Protein and B Vitamins.
    • Good source of Iodine (Iodide).
  • Oily Fish (e.g., Salmon, Mackerel, Sardines):
    • Contains high levels of fat, but these are Polyunsaturated fats.
    • Rich in Omega-3 fatty acids (important for heart health and brain function).
    • Vitamins A and D.

1.4 Meat (Beef, Chicken, Lamb, Pork)

Meat provides concentrated nutrition, especially red meat.

  • Nutritive Value:
    • Protein: Excellent source of HBV protein.
    • Minerals: Rich in Haem Iron (the type of iron most easily absorbed by the body) and Zinc.
    • Vitamins: Significant source of B Vitamins (Thiamin, Riboflavin, Niacin, and B12).
    • Fats: Varies widely. Lean cuts have less fat; visible fat is often saturated.
  • Common Mistake to Avoid: When cooking meat, remember that excessive heat can destroy B vitamins.

1.5 Soya

Soya (and soya products like tofu, tempeh, and textured vegetable protein) is a key ingredient in vegetarian diets.

  • Nutritive Value:
    • Protein: Contains all essential amino acids, making it one of the few plant sources that provides a complete protein (close to HBV).
    • High in B Vitamins, Iron, and Calcium (if fortified).
    • Relatively low in saturated fat.

Quick Review: Protein Sources
HBV sources = Meat, Fish, Eggs, Dairy, Soya.
If you need Iron = Meat (Haem Iron) and Eggs.
If you need Calcium = Dairy.

2. Cereals: Staple Foods and Energy Providers

Cereals form the foundation of most global diets. They are primarily valued for providing energy in the form of starch.

2.1 Composition and Value of Main Cereals

Cereals are the edible seeds or grains of grasses. The main types in the IGCSE syllabus are: Maize, Millets, Oats, Rice, and Wheat.

  • Nutritive Value (General):
    • Carbohydrates: The main nutrient is starch (a polysaccharide), providing essential energy.
    • Protein: Contains some Low Biological Value (LBV) protein.
    • NSP/Fibre: Found mainly in the outer layers (bran). Whole grains are high in NSP.
    • Vitamins and Minerals: B Vitamins (especially Thiamin and Niacin) and Iron. These are concentrated in the germ and outer layers.

2.2 Processing and Nutritional Loss

The nutritional value of cereals depends heavily on how they are processed:

  • Whole Grain (e.g., Brown Rice, Wholemeal Wheat): The entire grain is used, retaining the bran (fibre/vitamins) and germ (oils/vitamins). Highly nutritious.
  • Refined Grain (e.g., White Rice, White Flour): The bran and germ are removed to improve texture and shelf-life. This process removes much of the NSP/fibre and B vitamins.

2.3 Specific Cereal Examples

  • Wheat: Used for bread, pasta, cakes. The protein gluten allows dough to rise.
  • Rice: A global staple. Brown rice offers more fibre and B vitamins than white rice.
  • Oats: Known for containing soluble fibre (which helps lower blood cholesterol). Popular for breakfast.
  • Maize (Corn): Can be ground into flour or polenta. Used widely in Central and South America.

Quick Review: Cereals
Main role = Energy (Starch).
Best sources of Fibre/Vitamins = Whole grains (less processed).

3. Fruits, Vegetables, Pulses, and Nuts

These foods are essential for providing protective nutrients (vitamins, minerals) and fibre.

3.1 Fruits and Vegetables

These are the body’s maintenance crew, keeping systems running smoothly.

  • Nutritive Value:
    • Vitamins: Excellent sources of Vitamin C (citrus fruits, berries) and Vitamin A (carotenes, found in orange/yellow vegetables like carrots and dark green leafy vegetables).
    • Minerals: Potassium, Magnesium, and various trace elements.
    • NSP/Fibre: Provides bulk, helping digestion and preventing constipation.
    • Water: High water content, aiding hydration.
    • Carbohydrate: Fruits contain simple sugars (monosaccharides and disaccharides).
  • Note on Nutritive Value: Cooking can destroy some heat-sensitive vitamins, especially Vitamin C.

3.2 Pulses (Legumes)

Pulses include dried peas, beans, and lentils. They are often used as a cheaper alternative to meat.

  • Nutritive Value:
    • Protein: Good source of LBV protein. Must be eaten alongside cereals (like rice) to create a complete HBV meal.
    • Carbohydrates: Starch.
    • NSP/Fibre: Extremely high in dietary fibre.
    • Minerals: Good source of Iron (non-haem iron) and B Vitamins.

3.3 Nuts

Nuts (such as peanuts, almonds, and walnuts) are energy-dense foods.

  • Nutritive Value:
    • Fats: Very high in fat, but mainly healthy unsaturated fats.
    • Protein: LBV protein.
    • Vitamins/Minerals: B Vitamins and various minerals like Magnesium.
  • Safety Note: Due to their high energy content, nuts should be consumed in moderation as part of a balanced diet.

4. Fats and Oils

Fats and oils are the most concentrated source of energy in the diet. They also play a crucial role in carrying certain vitamins.

4.1 Composition and Value

Fats are typically solid at room temperature (e.g., butter, lard), while oils are liquid (e.g., olive oil, sunflower oil).

  • Nutritive Value:
    • Energy: Fats provide 9 kcal per gram, more than double the energy provided by carbohydrates or protein (4 kcal per gram).
    • Vitamin Carriers: They carry the four fat-soluble vitamins: A, D, E, and K.
    • Essential Fatty Acids (EFAs): These are fatty acids the body cannot make itself and must get from the diet (found in certain oils and oily fish).

4.2 Types of Fats (Brief Recall)

Fats are generally divided into two main types:

  • Saturated Fats: Generally found in animal products (e.g., meat fat, dairy cream). Too much saturated fat is linked to heart disease.
  • Unsaturated Fats (Mono- and Polyunsaturated): Found in plant sources (oils, nuts, seeds) and oily fish. These are considered healthier alternatives.

Quick Review: Protective and Energy Foods
Fruits/Veggies = Vitamins C & A, NSP, Water.
Pulses = Iron, NSP, LBV Protein.
Fats/Oils = Energy, Carries Vitamins A, D, E, K.