Learning objectives • To define energy and explain why it is needed. • To identify sources of energy in the diet. • To understand how energy needs change throughout life. • To understand the energy needs of different activities. • 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 = 1000J 1MJ = 1000kJ 1kcal = 1000cal 1kcal = 4.18kJ
Energy from food 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).
Energy providing nutrients 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. People who regularly consume excessive amounts of alcoholic drinks derive much of their energy intake from alcohol. They may also suffer from nutritional deficiencies and alcohol related diseases, e.g. liver disease and Warnicke-Korsakoff syndrome.
Energy in the diet The energy provided by a food or drink depends on the amount of carbohydrate, protein, alcohol and fat it contains. Gram for gram, carbohydrate provides less energy than protein, fat and alcohol. Look closely at the following examples of foods high in carbohydrate, fat and protein.
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 Total energy 3061.0kJ Carbohydrate 0.0kJ Fat 3052.5kJ Protein 8.5kJ
Energy in the diet – canned tuna 100g Total energy 421.7kJ Carbohydrate 0.0kJ Fat 22.2kJ Protein 399.5kJ
Energy intakes Experts have estimated the average requirements for energy for different types of people. These figures are known as Estimated Average Requirements (EAR) for energy. Experts also recommended that: • about 50% of our energy intake should come from carbohydrate; • no more than 35% of our energy intake should come from fat; • about 15% of our energy intake should come from protein.
Energy intakes 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 a person uses energy to maintain the basic functions of the body e.g. breathing. BMR is measured when a person is at complete rest, and varies between person to person. Men usually have a higher BMR than women because they tend to have a larger muscle mass. The BMR accounts for 75% of an individual’s energy needs.
Activity levels The total amount of energy required by an individual depends on their level of activity. The more active an individual is, the more energy they need.
Being active everyday It is recommended that children and young people 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 relatively 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. They are also often very active.
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 milk production.
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. It is advisable that older people consume food and drinks that are low in energy but high in vitamins and minerals to meet their requirements. These foods are known as nutrient dense foods.
Energy balance To maintain body weight it is necessary to balance the energy derived from food with that expended in activity. Energy balance is achieved when energy intake equals energy expenditure. It is important to maintain a healthy weight or avoid becoming overweight or underweight, both of which 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 are in positive energy balance over an extended period of time (i.e. they take in more energy than 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. Being overweight or obese is associated with an increased risk of developing certain cancers, cardiovascular disease and type 2 diabetes.
Negative energy balance A person is said to be in negative energy balance when there is insufficient energy from the diet to meet energy demands of the body. Energy is derived from energy stores and the person looses 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 over a period of time, the body derives energy from fat stores leading to weight loss. When too much fat is lost, the person becomes underweight. Being underweight is associated with health problems, such as osteoporosis, infertility and heart failure.
Monitoring energy balance For adults, change in weight is a good guide to energy balance. The Body Mass Index (BMI) is a good indicator of whether 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 intake with energy expenditure.
Calculating BMI kg . m2 Step 1 Height in meters (m) x height in metres (m) Step 2 Divide weight in kilograms (kg) by step 1 Step 3 Equals BMI. Next refer to guide below. Recommended BMI range Underweight less than 18.5 Normal 18.5 - less than 25 Overweight 25 - less than 30 Obese 30 - 40 Very obese over 40
Calculating BMI Calculate these 3 examples: 1. Samantha Height: 1.70m Weight: 51kg 2. Dale Height: 1.95m Weight: 82kg 3. Ruth Height: 1.63m Weight: 78kg Recommended BMI range Underweight less than 18.5 Normal 18.5 - less than 25 Overweight 25 - less than 30 Obese 30 - 40 Very obese over 40 kg . m2 BMI =
BMI example 1 Samantha Height: 1.70m Weight: 51kg 51kg . 1.7m x 1.7m BMI = 17.6 Samantha is underweight. Recommended BMI range Underweight less than 18.5 Normal 18.5 - less than 25 Overweight 25 - less than 30 Obese 30 - 40 Very obese over 40
BMI example 2 Dale Height: 1.95m Weight: 82kg 82kg . 1.95m x 1.95m BMI = 21.6 Dale is a healthy weight. Recommended BMI range Underweight less than 18.5 Normal 18.5 - less than 25 Overweight 25- less than 30 Obese 30- 40 Very obese over 40
BMI example 3 Ruth Height: 1.63m Weight: 78kg 78kg . 1.63m x 1.63m BMI = 29.4 Ruth is overweight. Recommended BMI range Underweight less than 18.5 Normal 18.5 - less than 25 Overweight 25- less than 30 Obese 30- 40 Very 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 understand how energy needs change throughout life. • To understand the energy needs of different activities. • To define energy balance. • To explain problems associated with energy imbalance.
For more information visit www.nutrition.org.ukwww.foodafactoflife.org.uk