Malnutrition/obesity overview - Biology IGCSE Study Notes

Malnutrition is a condition arising from an unbalanced diet where nutrients are either insufficient, excessive, or in incorrect proportions. It encompasses both undernutrition (deficiency) and overnutrition (excess).

Key Terms:

Undernutrition occurs when the diet lacks sufficient nutrients or energy, leading to conditions like:

• Starvation: severe lack of energy (calories/kilojoules)
• Protein-energy malnutrition: deficiency in protein and energy
• Vitamin/mineral deficiencies: lack of specific micronutrients (e.g., scurvy from vitamin C deficiency, anaemia from iron deficiency)

Overnutrition results from excessive nutrient intake, particularly:

• Obesity: excess body fat accumulation from consuming more energy than expended
• Vitamin toxicity: rare but possible from excessive vitamin supplements

Obesity is specifically defined as having a Body Mass Index (BMI) ≥ 30 kg/m².

Formula: BMI = mass (kg) ÷ [height (m)]²

Healthy BMI range: 18.5–24.9 kg/m²

Causes of malnutrition:

• Poverty and food insecurity
• Unbalanced diet choices
• Lack of nutritional knowledge
• Medical conditions affecting absorption
• Eating disorders

Consequences include weakened immunity, poor growth, increased disease risk, organ damage, and reduced life expectancy. Both forms severely compromise health, though they manifest differently.

Cambridge Note: Questions often ask you to distinguish between types of malnutrition and explain causes/effects separately.

Think of your body as a complex factory requiring precise raw materials. Too few materials (undernutrition) means production halts; too many (overnutrition) causes storage overflow and machinery damage.

Real-World Undernutrition Example: In regions experiencing drought in Sub-Saharan Africa, children develop kwashiorkor (protein deficiency despite adequate calories) showing swollen bellies, thin muscles, and reddish hair. Their bodies break down muscle tissue for protein, weakening immune systems. This explains why infectious diseases become lethal—the body lacks resources to mount defences.

Real-World Obesity Example: In developed countries like the UK and USA, sedentary lifestyles combined with readily available high-sugar, high-fat processed foods create an energy surplus. A person consuming 2,500 kcal daily but only expending 2,000 kcal stores 500 kcal as fat—approximately 50g daily. Over one year, this equals 18 kg of fat gain!

The Obesity Cascade: Excess weight → increased strain on joints (osteoarthritis) → reduced mobility → less exercise → further weight gain. Additionally, fatty deposits in blood vessels (atherosclerosis) narrow arteries, raising blood pressure and heart disease risk. The pancreas overworks producing insulin (Type 2 diabetes develops when cells become resistant).

Economic Impact: The NHS spends over £6 billion annually treating obesity-related conditions. Malnourished populations show reduced workplace productivity, creating poverty cycles.

Memory Aid: "FOOD = Fuel Only, Obesity Develops" when intake exceeds output.