Energy

© Food – a fact of life 2009

Energy

Extension


Learning objectives

• To define energy and explain why it is needed.

• To identify sources of energy in the diet.

• To identify the body’s energy needs.

• To describe energy needs throughout life.

• To explain different activity levels.

• To define energy balance.

• To explain problems associated with energy imbalance.


What is energy?

Energy is the power used to do work or to produce heat or light. Energy cannot be created or destroyed, but can be changed from one form to another.

It is measured in kilojoules (kJ) or megajoules (MJ).

When using imperial measurements, kilocalories (kcal) are used.

1kJ = 1000J1MJ = 1000kJ1kcal = 1000cal1kcal = 4.18kJ


Examples of energy

When we consume food and drink, energy provided by carbohydrate, protein, and fat (and alcohol) is metabolised and used by our bodies.

Carbohydrate, protein, and fat (and alcohol) are broken down into smaller compounds which are then oxidised in the cells of the body (respiration).


Where does energy come from?

Energy in the diet is provided by the nutrients carbohydrate, protein, and fat.

1 gram of carbohydrate provides16kJ.

1 gram of protein provides17kJ.

1 gram of fat provides 37kJ.


Energy in the diet - alcohol

Alcohol also provides the body with energy.However, it is not considered a nutrient, because it

is not essential for survival.

1 gram of alcohol provides 29kJ.

For people who drink a lot of alcohol, it may form a large part of their energy intake. This may lead to nutritional deficiencies and several alcohol related diseases, e.g. liver disease and Warnicke-Korsakoff syndrome or beri beri.


Energy in the diet

The energy provided by a food depends on how many grams of carbohydrate, protein and fat are present.

Gram for gram, carbohydrate provides less energythan protein, fat and alcohol.

Look closely at the following examples of foods high in

carbohydrate, fat and protein foods.


Energy in the diet - white bread 100g

Total energy 931.0kJ

Carbohydrate 737.6kJ

Fat 59.1kJ

Protein 134.3kJ


Energy in the diet - butter 100g


Carbohydrate 0.0kJ

Fat 3052.5kJ

Protein 8.5kJ


Energy in the diet – canned tuna 100g


Carbohydrate 0.0kJ

Fat 22.2kJ

Protein 399.5kJ


What is the main source of energy?

Per 100g Energy Carbohydrate

Fat Protein

White bread

931.0kJ 737.6kJ 59.1kJ 134.3kJ

Butter 3061.0kJ

0.0kJ 3052.5kJ 8.5kJ

Canned tuna

422.0kJ 0.0kJ 22.2kJ 399.5kJ

Picture


Dietary reference values (DRVs)

The average energy intake in the UK for young people

aged 15 - 18 years is:● 8830 kJ for girls.● 11510 kJ for boys.

However, requirements vary from person to person depending on a variety of factors, including physical activity level.


Energy expenditure

Different people need different amounts of energy, depending on a variety of factors, including their:

• basal metabolic rate (BMR);• level of physical activity;• age;• sex;• body size.


Basal metabolic rate

The basal metabolic rate (BMR) is the rate at which aperson uses energy to maintain basic functions of thebody e.g. breathing. BMR is measured when a personis at complete rest, and varies between person toperson.

Men usually have a higher BMR than women becausethey tend to have a larger muscle mass.

The BMR accounts for 75% of an individual’s energyneeds.


Activity levels

The total amount of energy required by an individual

depends on their level of activity. The more active they are, the more energy they need.


Do people need to be more active?

Yes! Children and young people need to participate in at least 60 minutes of moderate intensity

everyday where breathing rate and heart rate increase.

Activities that increase muscle strength and flexibility

as well as bone strength, should also be included once a week.

Regular activity will help maintain energy balance.


Energy needs of children

Infants and children have large energy requirements because they are active and growing.

Infants and young children have a higher BMR in relation to their size because energy is needed for growth.


Energy needs of adolescents

Adolescents have high energy requirements due to the body changes they experience from 11-18 years of age.

Energy needs for female and male adolescents will differ slightly as changes in their development occur at slightly different ages.


Energy needs of adults (19-50 years)

Adult energy requirements are lower than those of adolescents.

However, during pregnancy and lactation (breastfeeding) there is an increased need for energy for the growing fetus and infant.


Energy needs of adults 50 years and over

Energy requirements decrease gradually after the age of 50 years in women and 60 years in men.

The food and drink these people consume need to be lower in energy and higher in vitamins and minerals to meet their requirements. This is called nutrient dense food.


Energy balance

If an adult takes in the right amount of energy from food and drink to meet their needs, they will remain the same weight. This is called energy balance, where energy intake equals energy expenditure.

This should be achieved over a period of time tomaintain a healthy weight.

It is important to maintain a healthy weight oravoid becoming overweight or underweight, both ofwhich are major public health problems in the UK.


Positive energy balance

When the diet provides more energy than is needed, it is stored as fat and the person puts on weight over time.

People who have a positive energy balance over an extended period of time (i.e. they take in more

energythan they use) are likely to become overweight or obese.


Overweight and obese

Excess energy is stored in adipose tissue and can build up if energy intake continues to be too high, or activity levels remain too low.

Increasing levels of overweight and obesity are associated with an increased risk of developing certain cancers, cardiovascular disease and type 2 diabetes.


Negative energy balance

When the diet does not provide the energy needed, negative energy balance is achieved.

The person uses their stores of energy and loses weight.

People who achieve a negative energy balance over an extended period of time, are likely to become underweight.


Underweight

When too little energy is consumed by the body over a period of time, the body uses fat stores leading to weight loss.

When too much fat is used by the body, the body becomes underweight.

This can be associated with health problems, e.g. osteoporosis, infertility and heart failure.


Monitoring energy balance

For adults, change in weight is a good guide toenergy balance.

The Body Mass Index (BMI) is a good indicator if a person is underweight, overweight or a healthy weight.

The BMI range should only be used for people aged 18 years of age and over.

We are all encouraged to maintain a healthy weight by balancing energy input and energy expenditure.


Calculating BMI

Step 1 Height in meters (m) x height in meters (m)

Step 2 Divide weight in kilograms (kg) by step 1

Step 3 Equals BMI. Next refer to guide below.

kg . m2

Recommended BMI rangeUnderweight less than 18.5Normal 18.5 - less than 25Overweight 25 - less than 30Obese 30 - 40Very obese over 40


Calculating BMI

Calculate these 3 examples:

kg . m2

1. Samantha

Height: 1.70m

Weight: 51kg

2. Dale

Height: 1.95m

Weight: 82kg

3. Ruth

Height: 1.63m

Weight: 78kg

BMI =



BMI example 1

51kg . 1.7m x 1.7m

BMI = 17.5

Samantha

Height: 1.70m

Weight: 51kg

Samantha is underweight.



BMI example 2

82kg . 1.95m x 1.95m

BMI = 21.5

Dale

Height: 1.95m

Weight: 82kg

Dale is a healthy weight.

Recommended BMI rangeUnderweight less than 18.5Normal 18.5 - less than 25Overweight 25- less than 30Obese 30- 40Very obese over 40


BMI example 3

78kg . 1.63m x 1.63m

BMI = 29

Ruth

Height: 1.63m

Weight: 78kg

Ruth is overweight.

Recommended BMI rangeUnderweight less than 18.5Normal 18.5 - less than 25Overweight 25- less than 30Obese 30- 40Very obese over 40


Review of the learning objectives

• To define energy and explain why it is needed.

• To identify sources of energy in the diet.

• To identify the body’s energy needs.

• To describe energy needs throughout life.

• To explain different activity levels.

• To define energy balance.

• To explain problems associated with energy imbalance.


For more information visit

www.foodafactoflife.org.uk

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Energy