Food and Nutrition (0648) | Nutritive value of food

Welcome to Chapter 2: Nutritive Value of Food!

Hello future nutrition experts! This chapter is the heart of Food and Nutrition. We will be learning what makes up the food we eat—its true value beyond just taste. Understanding the nutritive value of food means knowing exactly what job each nutrient does in your body, from providing energy to building bone.

Think of your body as a sophisticated machine. Nutrients are the fuel, the repair kits, and the oil that keep everything running smoothly! Don't worry if the names seem complicated; we’ll break down each one into simple, memorable facts.

Key Nutrients Overview

We divide nutrients into two main groups:

• Macronutrients: Needed in large amounts (Carbohydrates, Fats, Proteins). They provide energy.
• Micronutrients: Needed in small amounts (Vitamins and Minerals). They help regulate body processes.

We also include Water and Non-Starch Polysaccharide (NSP) / Fibre, which are essential for health.

Section 1: Macronutrients (The Energy Providers)

1. Proteins: The Building Blocks

Function: Proteins are essential for growth and repair of all body tissues (muscles, skin, hair, internal organs). They also help produce enzymes and hormones.

Biological Value of Protein

This describes how well the protein is used by the body, based on its amino acid content.

• High Biological Value (HBV): These foods contain all the essential amino acids your body needs. They are usually found in animal sources.
  • Sources: Meat, fish, poultry, eggs, dairy products (milk, cheese), and soya.
• Low Biological Value (LBV): These foods are missing one or more essential amino acids. They are mainly found in plant sources.
  • Sources: Cereals (wheat, rice), pulses (beans, lentils), nuts, and seeds.

2. Carbohydrates: The Main Fuel

Function: Carbohydrates are the body's primary and cheapest source of energy. They are classified based on the complexity of their sugar units.

Types of Carbohydrates

• Monosaccharide (Single Sugar Unit): These are digested quickly, giving instant energy.
  • Example: Glucose (found in fruits, honey).
• Disaccharide (Two Sugar Units): Also sweet and quickly digested.
  • Examples: Sucrose (table sugar), Lactose (milk sugar).
• Polysaccharide (Many Sugar Units): Also known as starch. These are complex, taking longer to break down, providing sustained energy.
  • Sources: Bread, pasta, rice, potatoes, cereals.

3. Fats (Lipids)

Function: Fats provide a concentrated source of energy (more than double that of carbohydrates or protein). They also provide insulation, protect vital organs, and carry the fat-soluble vitamins (A, D, E, K).

Sources: Butter, oils, lard, nuts, fatty fish, meat, and cream.

Key Takeaway for Macronutrients: Proteins build and repair; Carbohydrates provide quick/primary energy; Fats provide concentrated energy and insulation.

Section 2: Sources and Uses of Food Energy

Energy Measurement

When we talk about the energy released from food, we measure it in Kilojoules (kJ) or Kilocalories (kcal) (often just called Calories).

All macronutrients provide energy, but in different amounts:

• Fats: Highest energy density.
• Carbohydrates: Primary energy source.
• Proteins: Used for energy only if carbohydrates and fats are insufficient.

The energy released from food is used for three main purposes (the uses of food energy):

1. Basal Metabolic Rate (BMR): Energy needed to keep essential processes going while the body is at rest (breathing, heart beating, maintaining body temperature). This is the biggest use of energy.
2. Physical Activity: Energy needed for movement, exercise, and working.
3. Thermic Effect of Food: Energy needed to digest, absorb, and store food.

Section 3: Non-Starch Polysaccharide (NSP) / Dietary Fibre

NSP is a type of carbohydrate that our bodies cannot digest, meaning it provides almost no energy.

Function: NSP acts like a 'scrubbing brush' or 'bulk' in the digestive system.

• It adds bulk to the faeces, preventing constipation.
• It helps maintain peristalsis (the wave-like movement that pushes food through the gut).
• It helps you feel full (satiety), which is helpful for weight control.

Sources: Wholemeal bread and pasta, fruits (especially the skin), vegetables, pulses, and nuts.

Section 4: Micronutrients – Vitamins

Vitamins are organic substances needed in small amounts to help regulate chemical reactions in the body. They are divided into two categories:

A. Fat-Soluble Vitamins (A, D, E, K)

These are stored in the body's fat reserves, so you don't need to eat them every day. However, too much can be toxic (hypervitaminosis).

Vitamin A (Retinol)

• Function: Essential for good vision (especially in dim light), healthy skin, and fighting infection.
• Sources: Liver, oily fish, egg yolk, milk. Carotene (the plant form) is found in carrots, dark green leafy vegetables.

Vitamin D (Calciferol)

• Function: Helps the body absorb calcium and phosphorus, crucial for strong bones and teeth.
• Sources: Oily fish, eggs, fortified cereals. (Also synthesized by the skin upon exposure to sunlight).

Vitamin E (Tocopherol)

• Function: Acts as an antioxidant, protecting cell membranes.
• Sources: Vegetable oils, wholemeal products, nuts, and seeds.

Vitamin K

• Function: Essential for normal blood clotting.
• Sources: Green leafy vegetables (spinach, cabbage), made by bacteria in the gut.

B. Water-Soluble Vitamins (C and B Group)

These cannot be stored by the body (except Cobalamin/B12). Any excess is simply passed out in the urine, so they must be consumed regularly. They are easily destroyed by heat and water during cooking.

Vitamin C (Ascorbic Acid)

• Function: Essential for a healthy immune system, healing wounds, and helps the absorption of iron.
• Sources: Citrus fruits, blackcurrants, green vegetables, potatoes.

The B Group Vitamins (B1, B2, Niacin, B12)

The B vitamins often work together and are key in releasing energy from food (metabolism).

• Thiamin (B1): Helps the nervous system function and releases energy from carbohydrates.
  • Sources: Whole grains, nuts, pork.
• Riboflavin (B2): Important for energy release and healthy skin/eyes.
  • Sources: Milk, cheese, eggs, liver.
• Nicotinic Acid (Niacin): Also essential for energy release, healthy skin, and nervous system.
  • Sources: Meat, fish, wheat flour.
• Cobalamin (B12): Needed for the formation of healthy red blood cells and normal nerve function.
  • Sources: Only found naturally in animal products (meat, fish, eggs, milk).

Section 5: Micronutrients – Mineral Elements

Minerals are inorganic substances that help build structures (like bones) and regulate body processes (like fluid balance).

Calcium (Ca)

• Function: Vital for strong bones and teeth. Also helps with muscle contraction and blood clotting.
• Sources: Milk, cheese, yoghurt, green leafy vegetables (e.g., kale).

Iron (Fe)

• Function: Essential component of haemoglobin, which carries oxygen in the blood. Prevents anaemia.
• Sources: Red meat (HBV iron), liver, eggs, dark green vegetables, fortified cereals (LBV iron).

Phosphorus (P)

• Function: Works closely with calcium for bone formation; part of energy compounds (ATP).
• Sources: Meat, fish, dairy, cereals.

Sodium (Na)

• Function: Maintains fluid balance in the body and nerve function.
• Sources: Salt (sodium chloride), processed foods. (Note: Too much sodium is linked to high blood pressure.)

Potassium (K)

• Function: Works with sodium to regulate fluid balance and maintain healthy muscle and nerve function.
• Sources: Bananas, vegetables, fruit, meat.

Iodide (Iodine)

• Function: Needed to produce thyroid hormones, which regulate metabolism.
• Sources: Seafood, iodised salt, dairy products.

Fluoride (F) and Chloride (Cl)

• Fluoride: Strengthens tooth enamel and helps prevent dental decay. Sources: Fluoridated water, tea.
• Chloride: Important for fluid balance and producing hydrochloric acid in the stomach (for digestion). Sources: Salt.

Section 6: Water (H₂O)

Water is not a nutrient in the technical sense, but it is the most essential chemical component of the body, making up about 60% of our weight.

Function: Water is the solvent for life!

• It transports nutrients and waste products around the body (e.g., in blood).
• It helps regulate body temperature (through sweat).
• It is essential for most chemical reactions in the body.
• It lubricates joints and membranes.

Sources: Drinking water, beverages, and most foods (especially fruits and vegetables) contain significant water.