Obesity, Malnutrition and Lifestyle Factors

Smoking also devastates the respiratory system:

• Tar: This sticky substance is a powerful carcinogen that mutates lung and throat cell DNA, leading to cancer. It also paralyses the cilia in the airways, leading to chronic bronchitis.
• Emphysema: Smoke triggers the immune system to send phagocytes into the lungs. These cells release elastase, an enzyme that breaks down the elastic fibres of the alveoli. The alveoli eventually burst and fuse together, drastically reducing the surface area available for gas exchange.

Diet, Exercise, and Malnutrition

The food we eat literally builds and fuels our cells, making diet one of the most powerful influences on our long-term health.

A diet chronically deficient or excessive in nutrients leads to malnutrition. Undernutrition causes deficiency diseases like scurvy (lack of Vitamin C) or anaemia (lack of iron). Conversely, overnutrition leads to excessive fat storage.

• Dietary Risks: High intake of saturated fats directly contributes to atherosclerosis and cardiovascular disease. Meanwhile, diets heavy in refined carbohydrates force the body to constantly overproduce insulin. Over time, target cells stop responding to this hormone, a condition known as insulin resistance, which is the direct cause of Type 2 diabetes.
• The Role of Exercise: Regular physical activity shifts the energy balance. It increases energy expenditure, burning stored fat. It also builds muscle mass, which raises the body's Basal Metabolic Rate (BMR), meaning more calories are burned even at rest. Furthermore, exercise strengthens the heart muscle, lowering resting heart rate and blood pressure.

Analysing Obesity: BMI and Waist-to-Hip Ratio

Why might a heavy, muscular rugby player be classified by a doctor the same way as someone with a high body fat percentage?

Body mass is dictated by the energy balance: if energy intake (calories eaten) exceeds energy expenditure (calories burned), the excess is stored as fat. Severe excess fat accumulation is diagnosed as obesity.

Scientists use quantitative measurements to assess health risks. The most common is Body Mass Index (BMI).

• Underweight: $< 18.5$
• Healthy: $18.5$ to $24.9$
• Overweight: $25.0$ to $29.9$
• Obese: $\geq 30.0$

However, BMI has a major limitation: it cannot distinguish between fat and heavy muscle mass. Therefore, doctors also measure the waist-to-hip ratio to identify abdominal obesity (fat stored dangerously around the vital organs). A ratio above $0.90$ for men, or $0.85$ for women, indicates abdominal obesity and is a much stronger predictor of cardiovascular disease and Type 2 diabetes than BMI.

Worked Example: Calculating BMI

A patient has a mass of 88 kg and a height of 1.72 m. Calculate their BMI and state their weight category.

$BMI = \frac{\text{mass (kg)}}{(\text{height (m)})^2}$

Step 1: Square the height.

• $1.72^2 = 2.9584$

Step 2: Divide the mass by the squared height.

• $BMI = 88 \div 2.9584$

Step 3: Calculate and round to 3 significant figures.

• $BMI = 29.7$ kg/m²
• The patient is in the Overweight category.

Worked Example: Calculating Waist-to-Hip Ratio

A female patient has a waist circumference of 860 mm and a hip circumference of 0.98 m. Calculate her waist-to-hip ratio and determine if she has abdominal obesity.

$\text{Ratio} = \frac{\text{waist circumference}}{\text{hip circumference}}$

Step 1: Convert both measurements to the same unit (centimetres).

• Waist: $860$ mm = $86$ cm
• Hip: $0.98$ m = $98$ cm

Step 2: Substitute into the formula.

• $\text{Ratio} = 86 \div 98$

Step 3: Calculate and round to 2 decimal places.

• $\text{Ratio} = 0.88$
• Because $0.88 > 0.85$, the patient does have abdominal obesity.