The components of a balanced diet and the roles of nutrients, the consequences of dietary imbalance, the assessment of body mass using BMI, and the effects of regular physical exercise on the body systems and on health.

What this dot point is asking

CCEA wants you to describe the components of a balanced diet and the roles of the nutrients, explain the consequences of dietary imbalance such as obesity and deficiency diseases, use the body mass index (BMI) to assess body mass, and explain the effects of regular physical exercise on the body systems and on long-term health. It ties the whole unit together, linking diet and activity to the cardiovascular, respiratory and musculoskeletal systems.

Components of a balanced diet

Each component has a role. Carbohydrates are the main energy source, broken down to glucose for respiration. Lipids (fats) are a concentrated energy store, provide insulation and supply essential fatty acids; saturated fats in excess raise blood cholesterol. Proteins provide amino acids for growth and repair of tissues and to make enzymes. Vitamins are needed in small amounts for specific functions (vitamin C for connective tissue, vitamin D for calcium uptake). Minerals include calcium for bones and teeth and iron for haemoglobin. Fibre adds bulk so the gut can move food along, and water is the solvent for transport and reactions. The right balance depends on age, sex, activity level and condition (for example pregnancy increases needs for some nutrients).

Consequences of dietary imbalance

Both excess and deficiency therefore damage health. A diet high in saturated fat and salt raises cholesterol and blood pressure, increasing cardiovascular risk, while a diet low in fibre is linked to constipation and bowel problems. Public-health advice aims for a balance: enough energy for activity, plenty of fruit, vegetables and fibre, and limited saturated fat, salt and free sugars.

BMI and the effects of exercise

Body mass index (BMI) assesses whether body mass is healthy for height. It is calculated as mass in kilograms divided by the square of height in metres. Values are classified as underweight (below 18.5), healthy (18.5 to 24.9), overweight (25 to 29.9) and obese (30 or more). BMI is a useful screening tool but does not distinguish muscle from fat, so a very muscular person may have a high BMI without excess fat.

Regular physical exercise benefits the body systems: it strengthens cardiac muscle so the heart pumps more blood per beat and resting heart rate falls; it lowers blood pressure and helps reduce blood cholesterol, lowering the risk of coronary heart disease; it improves lung function and ventilation; it strengthens bones (weight-bearing exercise) and builds muscle; it helps control body mass by using energy; and it reduces the risk of type 2 diabetes and improves mental well-being. These effects connect directly to the cardiovascular, respiratory and musculoskeletal systems studied earlier in the unit.

Examples in context

Example 1. Diet and coronary heart disease. A diet high in saturated fat and salt raises blood cholesterol and blood pressure, promoting atheroma in the coronary arteries and raising the risk of a heart attack. Reducing saturated fat and salt, eating more fibre, and exercising regularly lowers these risk factors, directly linking nutrition to the cardiovascular system.

Example 2. Exercise and resting heart rate. A person who trains regularly develops a stronger heart with a larger stroke volume, so the same cardiac output is achieved at a lower heart rate; their resting pulse may fall from about 75 to below 60 beats per minute. Monitoring resting heart rate is one way to track improving fitness, connecting exercise to cardiovascular health.

Try this

Q1. State the role of protein in the diet and one consequence of protein deficiency. [2 marks]

• Cue. Growth and repair of tissues (and making enzymes); deficiency impairs growth and tissue repair.

Q2. A person has a mass of 80 kilograms and a height of 2.00 metres. Calculate their BMI. [2 marks]

• Cue. $80 / 2.00^2 = 80 / 4 = 20 \ \text{kg m}^{-2}$ (healthy range).

Q3. State two ways regular exercise benefits the cardiovascular system. [2 marks]

• Cue. Strengthens the heart and increases stroke volume; lowers resting heart rate and blood pressure; reduces blood cholesterol.