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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
InsulationATP if not
enough 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 = 850kj
Energy Expenditure for the day = 6623 + 850 + 1806 = 9279kj
Energy 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.
2))((
)(
mHeight
kgweightBMI
BMI
Women Men
Underweight <18 <19
Healthy weight
19-24 20-25
Overweight 25-30 26-30
Obese >30 >30
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