BMR and PAL help explain how a person’s energy needs are estimated. In AQA GCSE Food Preparation and Nutrition, you need to understand that the body uses energy to stay alive and carry out physical activity. Basal metabolic rate, or BMR, is the energy needed for essential body processes when the body is at rest. Physical activity level, or PAL, allows for the energy used through movement and activity. Together, BMR and PAL help estimate a person’s total energy requirement.
What is basal metabolic rate?
Basal metabolic rate (BMR) is the amount of energy the body needs to maintain essential functions when it is resting. These functions include breathing, keeping the heart beating, maintaining body temperature and supporting the activity of organs.
Even when a person is asleep or lying still, their body continues to use energy. BMR therefore represents the energy needed for survival before extra activity, such as walking to school, cooking or playing sport, is considered.
What affects BMR?
BMR is not exactly the same for everyone. It can be affected by factors such as:
- body size and mass
- the proportion of muscle in the body
- age
- sex
- genetic differences.
For example, muscle tissue is metabolically active, meaning it uses energy even when the body is resting. This helps explain why two people of the same age may have different BMRs. In an exam answer, avoid suggesting that one single BMR applies to every person.
What is physical activity level?
Physical activity level (PAL) is a factor used to represent how active a person is. It takes account of energy used for movement and physical activity in addition to the energy needed for basic body functions.
A person with a low level of activity will have a lower PAL than someone who is regularly active. For example, a person who spends much of the day sitting will usually have different energy needs from someone who walks a lot, has a physically active job or trains regularly.
PAL is not a description of one short activity. It is used to reflect a person’s overall activity level. This means that a realistic judgement should consider the person’s usual daily pattern rather than focusing only on one exercise session.
How BMR and PAL are used together
Energy requirement can be estimated using the relationship:
Energy requirement = BMR × PAL
This shows that BMR provides the starting point and PAL adjusts the estimate according to activity. If two people have the same BMR but different activity levels, the person with the higher PAL will have the higher estimated energy requirement.
A worked example
Imagine a person has a BMR of 6,000 kilojoules per day and a PAL of 1.5. Their estimated energy requirement would be:
6,000 × 1.5 = 9,000 kilojoules per day
This is an example of applying the relationship, not a universal recommendation. In a real situation, energy needs vary between individuals and may change over time.
Energy balance and energy needs
Energy balance describes the relationship between energy taken in from food and energy used by the body. If energy intake is broadly similar to energy expenditure over time, body mass is more likely to remain stable. If energy intake is regularly greater than energy expenditure, the excess may be stored by the body. If energy intake is regularly lower, stored energy may be used.
These ideas must be used carefully. A person’s energy needs depend on their individual circumstances, and body mass alone does not provide a complete picture of health. For GCSE answers, link BMR and PAL to the idea that people require different amounts of energy because their bodies and activity levels differ.
Applying BMR and PAL to food preparation
Understanding energy needs can help a food designer think about who a product is for. For example, a meal planned for an active teenager may need to provide a different amount of energy from a snack designed for someone with a less active routine. The portion size, ingredients and cooking method could all be considered alongside the target consumer.
However, BMR and PAL do not tell you everything about a healthy diet. A food product should also be considered in relation to nutrients, variety, portion size and the needs of the intended consumer. Do not assume that a food is suitable simply because its energy content is high or low.
Common mistakes to avoid
- Confusing BMR with total energy needs: BMR covers essential resting functions, not all daily activity.
- Forgetting what PAL means: PAL represents overall activity level, not the energy in a particular food.
- Mixing up intake and requirement: energy requirement is an estimate of what the body needs, while energy intake is supplied by food and drink.
- Giving a one-size-fits-all answer: BMR and PAL vary between individuals.
- Leaving out units: check whether the question uses kilojoules or another stated unit, and use it consistently.
Exam-ready retrieval checklist
- Can you define basal metabolic rate?
- Can you explain why the body needs energy when resting?
- Can you define physical activity level?
- Can you write energy requirement = BMR × PAL?
- Can you explain why two people may have different energy requirements?
- Can you apply the formula to a numerical example and include the correct unit?
Specification reminder
This guide supports AQA GCSE Food Preparation and Nutrition, specification section 3.2.3.2, Food, nutrition and health: Energy needs. Check the AQA specification and any current official guidance before publication or assessment, as specifications and guidance can change.
Frequently asked questions
Is BMR the same as the amount of energy a person needs in a day?
No. BMR is the energy needed for essential functions at rest. A person’s estimated daily energy requirement also considers activity through PAL.
Why does physical activity change energy needs?
Movement and exercise use energy in addition to the energy needed for essential functions. PAL allows this difference in activity to be included in an estimate.
Can BMR and PAL give an exact answer for everyone?
No. They provide an estimate. Individual factors and usual activity levels mean that energy needs differ between people.