Human Biology | Nutrition and energy

Welcome to Nutrition and Energy!

Hello everyone! In this crucial chapter, we're diving into how the food we eat keeps us alive, growing, and full of energy. Understanding nutrition isn't just about passing an exam; it's about making smart choices for a healthy life.
Don't worry if you find some of the terms tricky—we will break down every concept into bite-sized pieces! Let's find out exactly what your body needs to thrive.

Introduction to a Balanced Diet

A diet is simply everything you eat and drink. But a balanced diet is specific: it provides the correct amounts of all seven essential food components needed to maintain health.

Think of your body like a car: it needs fuel (carbohydrates/fats), oil (vitamins/minerals), and parts for maintenance (protein). If you only put in fuel, the engine will eventually break down!

The seven components of a balanced diet are:

• Carbohydrates (for energy)
• Fats (Lipids) (for energy, insulation, protection)
• Proteins (for growth and repair)
• Vitamins (for chemical reactions)
• Minerals (for structure and body processes)
• Water (the universal solvent)
• Fibre (Roughage) (for gut health)

Quick Review Tip: To remember the seven components, try the mnemonic: Please Find Warm Milk Concerning Very Funny things!

Section 1: The Major Food Components (Macronutrients)

Macronutrients are the components we need in large amounts, primarily for energy, growth, and repair.

1. Carbohydrates (Carbs)

Carbohydrates are your body's primary and preferred energy source. They are easily broken down to release energy quickly.

• Function: Provide energy for movement, warmth, and all bodily functions.
• Sources: Sugars (fruits, honey) and Starches (bread, potatoes, rice, pasta).

Did you know? Carbohydrates are typically stored in the body as glycogen (in the liver and muscles) for later use.

Key Takeaway: Carbs are the body's 'rocket fuel', providing quick energy.

2. Fats (Lipids)

Fats are often seen as bad, but they are absolutely essential! They provide more than twice the energy per gram compared to carbohydrates.

• Function A: Provide a stored, concentrated source of energy (secondary to carbs).
• Function B: Act as insulation (keeping you warm) and protection (cushioning organs).
• Function C: Help dissolve and absorb fat-soluble vitamins (A, D, E, K).
• Sources: Butter, oils, nuts, fatty meats, dairy products.

Analogy: Fats are like your body’s ‘winter coat’—they keep you warm and protect vital organs.

3. Proteins

Proteins are the 'building blocks' of the body. They are made up of smaller units called amino acids.

• Function A: Essential for growth in children and adolescents.
• Function B: Essential for repair of damaged tissues (muscles, skin, organs).
• Function C: Used to make vital components like enzymes, hormones, and antibodies.
• Sources: Meat, fish, eggs, dairy, beans, lentils.

Important Note: Proteins are only used for energy as a last resort, when carbohydrate and fat stores are completely depleted.

Section 2: Micronutrients and Essentials

Micronutrients (Vitamins and Minerals) are needed in small amounts but are critical for regulating body processes.

4. Vitamins

Vitamins act as co-factors, helping chemical reactions occur properly. We must get them from our diet.

We only need to focus on a few key ones for the exam:

• Vitamin C (Ascorbic acid): Needed for healthy skin, gums, and healing wounds. Sources: Citrus fruits, vegetables.
• Vitamin D: Needed for the absorption of calcium. Sources: Sunlight, oily fish, fortified milk.
• Vitamin A: Needed for good eyesight (especially in low light). Sources: Carrots, liver, green vegetables.

5. Minerals

Minerals are inorganic elements needed for healthy bones, blood, and nerves.

• Calcium: Needed for strong bones and teeth, and for blood clotting. Source: Milk, cheese, leafy greens.
• Iron: Needed to make haemoglobin, the molecule in red blood cells that carries oxygen. Source: Red meat, spinach, lentils.

6. Water

You are about 60-70% water! It is the most vital nutrient.

• Function A: Acts as a solvent, dissolving substances so they can be transported (like nutrients and waste) around the body.
• Function B: Controls body temperature through sweating (cooling by evaporation).
• Function C: Involved in many chemical reactions.

7. Fibre (Roughage)

Fibre is mainly cellulose from plant cell walls. It cannot be digested by humans, but it is essential!

• Function: Adds bulk to food, which stimulates the muscles of the digestive tract (a process called peristalsis).
• Benefit: Prevents constipation (difficulty passing waste).
• Sources: Whole grains, vegetables, fruits, bran.

Section 3: Energy Requirements

Energy is measured in units called Joules (J) or kilojoules (kJ). Sometimes you might see Calories (cal) or kilocalories (kcal), which is another unit of energy.

\(1 \text{ kJ} \approx 0.24 \text{ kcal}\)

Factors Affecting Energy Requirements

The amount of energy a person needs depends on several factors. Someone requiring 8,000 kJ per day will need different food from someone requiring 12,000 kJ per day.

1. Activity Level: The more active you are (e.g., a manual labourer vs. an office worker), the more energy you burn and the more you need.
2. Age: Children and teenagers need high energy (and protein) for growth. Elderly people generally require less energy.
3. Sex: Men generally have a higher energy requirement than women due to usually having a larger body mass and higher proportion of muscle tissue.
4. Pregnancy/Lactation: Pregnant and breastfeeding women require extra energy and nutrients to support the developing baby and milk production.
5. Body Mass: Larger individuals require more energy to maintain their body temperature and move around.

Common Mistake Alert! Students sometimes confuse the amount of food (bulk) with energy content. Example: A spoonful of oil contains far more energy than a bowl of lettuce, even though the lettuce is much bigger.

Section 4: Malnutrition and Diet-Related Diseases

Malnutrition means an unhealthy condition caused by a diet that lacks the correct balance of nutrients, either too much (over-nutrition) or too little (under-nutrition).

A. Under-nutrition (Deficiency Diseases)

1. Protein-Energy Malnutrition (PEM)

These conditions often affect children in developing countries due to poor diet quality.

• Kwashiorkor: Caused by a severe lack of protein, even if the calorie intake is adequate (though often insufficient). Symptoms include a swollen abdomen (oedema) due to fluid retention and growth failure.
• Marasmus: Caused by a severe lack of both protein AND calories (energy). Symptoms include extreme wasting (very thin arms and legs) and very low body weight.

2. Specific Vitamin and Mineral Deficiencies

• Iron Deficiency Anemia: Lack of iron causes the body to produce fewer red blood cells or red blood cells that cannot carry enough oxygen (due to low haemoglobin). Symptoms: extreme tiredness, paleness.
• Scurvy: Lack of Vitamin C. This leads to weak connective tissue, bleeding gums, and poor wound healing.
• Rickets: Lack of Vitamin D or Calcium. This causes bones to soften, leading to bowed legs and skeletal deformities, mainly in children. (The adult equivalent is Osteomalacia).

B. Over-nutrition

Obesity

Obesity is the condition of being severely overweight, defined by having too much body fat (lipid) accumulated.

When a person consistently consumes more energy than they use, the excess energy is stored as fat.

• Health Risks Associated with Obesity:
• Increased risk of developing Type 2 Diabetes.
• Increased risk of Coronary Heart Disease (CHD) and high blood pressure (hypertension).
• Increased strain on joints, leading to mobility problems.

Encouraging Thought: Remember, maintaining a balanced diet is a lifelong commitment. Understanding these nutritional roles helps you take control of your health!