Energy Metabolism and BMR

Energy Metabolism and BMR

Energy: Metabolism

‘Metabolism refers to chemical process that occur in the body that are necessary to maintain life.’ (Magee & Oliver 2010)

Metabolism involves two key processes: Catabolism

Substances are broken down into simpler substances. For example, carbohydrate is converted to glucose.

Anabolism Larger molecules or structures are built from smaller

ones. For example, proteins build body tissue. Energy is released during catabolic reactions

to create (adenosine triphosphate)

Carbohydrate Metabolism

Carbohydrates from food

Monosaccharides

Blood glucose Cellular use

ATPEnergy

Excess stored as glycogen

or converted to fat and stored

Stores brokendown to glucoseif needed for ATP

Lipid Metabolism

Lipids from food

Converted to glycerol

and fatty acids

Metabolised in liver to acetic acid

Cellular Use

Cell membranes Insulation

ATP if notenough glucose

Protein Metabolism

Protein Amino Acids

Cellular Use

Build and repair body

tissue

ATP only if inadequate glucose and

fats.Least preferred

option

Energy: Storage and Balance

Storage of metabolised food is essential for times of famine and when the body requires great energy output.

Storage occurs in cells in the form of either glycogen or triglycerides.

If the body’s energy needs are in balance, energy consumption equals energy expenditure.

Energy: Storage and Balance

The body requires energy for: Maintaining body temperature

(heat energy) Brain and nerve transmission

(electrical) Movement (mechanical) Digestion and Metabolism

(chemical energy)The energy is easily

transferred from one form to another depending on the body’s requirements.

Basal Metabolic Rate (BMR)

Only 30% of energy intake is used for physical activity.

Remaining 70% is used for all the other metabolic processes that occur in the body.

Basal energy is the minimum amount of energy used to maintain normal body temperature and muscle tone, to keep the heart beating and all vital organs functioning.

The rate at which energy is needed for these metabolic processes is called the Basal Metabolic Rate.

How to calculate BMR?

Females Males1kg of body weight burns

roughly 0.9 of a calorie per hour.

1kg of body weight burns roughly 1.0 calorie per hour.

70kg X 0.9 X 24 hours = 1512 calories per day

80kg X 1.0 X 24 hours = 1920 calories per day

To convert to kilojoulesCalories X 4.184 (4.2)

= 6350 kj/per day

To convert to kilojoulesCalories X 4.184 (4.2)

= 8064 kj/per day

Turn to p52 and complete activity 11.

Influences on BMR

Body size The larger the body the

greater the BMR due to increased energy demands

Body fat Fatty tissues have a lower

BMR than muscle tissue. Therefore, greater lean body tissue increases your metabolic rate, because it is an active tissue that burn kilojoules at a faster rate.

Influences on BMR

Hormones People with an overactive

thyroid have a higher BMR.Illness

Increased BMR as the body works harder to fight infection

Fasting Reduces BMR, because the

body conserves energy to keep vital organs functioning.

Influences on BMR

Drugs Caffeine and nicotine increase

BMR Anti-Depressants, social and

prescription drugs reduce BMRExercise

BMR increases during exercise. BMR remains high during intense prolonged activity.

Gender Males have an elevated BMR

than females

Influences on BMR

Climate Cold temperatures increase

BMR given the body uses energy to stabilise body temperature.

Age Decreases with age due to

less activity and reduce lean tissue

Energy Balance

To identify a person’s energy balance you must calculate energy intake and expenditure. If intake is higher than expenditure a person will store energy. If intake is lower than expenditure a person will burn energy.

To calculate daily energy intake list all the food and beverages consumed. Using a food kilojoule table work out their values.

Energy Expenditure for the day = BMR + thermic effect + exercise Calculate BMR Take into account the thermic effects of food (10%) Work out the kilojoule expenditure for various activities.

Thermic Effect of Food

‘…the energy used in digestion, absorption, metabolism and the storage of ingested nutrients.’

Thermic effect is estimated at 10% of energy intake.

Energy Expenditure Calculation Example (p53)

73kg female consuming 8500 kJ walked for 30 minutes using 462 kJ and cycled for 60 minutes using 1344 kJ

BMR = 73 X 0.9 X 24 = 1576.8 calories= 1576.8 x 4.2 = 6623kj

Thermic effect = .10 X 8500kj = 850kjEnergy Expenditure for the day = 6623 +

850 + 1806 = 9279kjEnergy balance = Intake – Expenditure8500kj – 9279kj= 779kj

Your Turn – Calculate Energy Balance

68kg male consuming 11000kjwho jogged for 30 minutes (300 calories) and cycled for 1.5 hours (420 calories)BMR = 68 x 1.0 x 24 = 1632calories

= 1632 x 4.2 = 6854kjThermic Effect = .10 x 11000kj = 1100kjEnergy Expenditure = 6854 + 1100 + 1260 +1764= 10978kjEnergy Balance = 11 000 – 10978

= 22kj

Your Turn – Calculate Energy Balance

Female 62kg consuming 6985 kJ and burning 486 calories in daily activities.

BMR = 62kg x 0.9 x 24 = 1339.2 = 1339.2 x 4.2 = 5625 kjThermic Effect = 6985 x .10 = 699kj

Energy Expenditure = 5625 + 699 + 2041 = 8365kjEnergy Balance = 6985 – 8365 = - 1380kj

Body Mass Index (BMI)

BMI is a measure of weight for height.

BMI does not distinguish between weight due to fat or weight due to muscle.

BMI data developed based on data from Anglo-Saxon background; thus, height, weight and fat distribution among different ethnic groups is not taken into account.

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mHeightkgweightBMI

BMI

Women Men

Underweight <18 <19

Healthy weight

19-24 20-25

Overweight 25-30 26-30

Obese >30 >30