Energy balance, basal metabolic rate and physical activity level, how the body uses energy from macronutrients, and the diet-related health problems caused by an unbalanced diet, including obesity, cardiovascular disease, type 2 diabetes, tooth decay and bone health.

What this dot point is asking

AQA wants you to explain how the body gains and uses energy, what BMR and PAL mean, and how an unbalanced diet leads to specific health problems. You should be able to link a dietary cause to a named disease.

Energy balance

• If intake = output, weight stays the same.
• If intake is greater than output, the excess is stored as fat and weight increases.
• If intake is less than output, stored fat is used and weight decreases.

Where the body's energy goes

Energy comes mainly from carbohydrate and fat, with protein used as a secondary source. Government guidance suggests roughly 50% of energy from carbohydrate, no more than 35% from fat and the rest from protein. Each macronutrient supplies a known amount of energy, which lets you calculate the energy in a food: protein and carbohydrate each give about 4 kcal per gram, and fat gives about 9 kcal per gram, more than twice as much. This is why high-fat foods are so energy-dense and easy to over-consume.

BMR varies between people. It is higher in those with more muscle (muscle is metabolically active), in larger and taller people, in men compared with women on average, and it falls with age, which is one reason energy needs drop in later life. Activity level then adds on top: a sedentary office worker adds far fewer kilocalories than a manual labourer or athlete. Matching intake to total output is the core of weight management.

Diet-related health problems

An unbalanced diet, often combined with low activity, causes several conditions:

• Obesity - too much energy stored as fat; raises the risk of many diseases.
• Cardiovascular disease - too much saturated fat and salt narrows and hardens arteries, causing heart disease, high blood pressure and stroke.
• Type 2 diabetes - linked to obesity and high sugar intake; the body stops responding to insulin.
• Tooth decay - frequent free sugars feed bacteria that produce acid which attacks enamel.
• Poor bone health - too little calcium and vitamin D weakens bones, causing rickets in children and osteoporosis in later life.

Each link has a mechanism worth naming. In cardiovascular disease, excess saturated fat raises blood cholesterol, which forms fatty plaques (atherosclerosis) that narrow arteries and can cause a heart attack or stroke; too much salt raises blood pressure, straining the heart and vessels. In type 2 diabetes, sustained high intake and obesity cause cells to become resistant to insulin, so blood glucose is no longer controlled. In tooth decay, oral bacteria ferment free sugars into acid that dissolves enamel. Naming the mechanism, not just the food, is what lifts a 6-mark answer.

Try this

Q1. Define basal metabolic rate. [1 mark]

• Cue. The energy the body needs to stay alive and function at rest.

Q2. Name two diseases linked to a diet too high in saturated fat and salt. [2 marks]

• Cue. Coronary heart disease, high blood pressure or stroke.