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METABOLISM 1Basal metabolic rate
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© Katarína Babinská MD, PhD, MSc, Institute of Physiology CU, Bratislava
Objectives
Basal metabolic rate (BMR)
Factors that influence the BMR
Methods of measurement of BMR
Daily energy expenditure
Physical activity level-PAL
Tasks
Measurement of the BMR
Calculation of daily energy expenditure
by tables
METABOLISM
- chemical reactions within in the cells
of the body
- continuous, life sustaining reactions
Two aspects of metabolism
• chemical conversion of substances
for tissue synthesis and operation of
the body (e.g. enzymes, hormones)
• conversion of chemical energy
provided by chemical bonds of
nutrients into energy utilizable in cells
(ATP and other high energy bonds)
and its utilization for vital functions
catabolism – „energy yielding metabolism“
– breakdown of substances (e.g.fat or glycogen stores in the body)
– energy (of the chemical bonds) is released in form of
• chemical energy - utilized for body functions
• heat – maintenance of the constant body temperature
– required for homeostasis and
metabolic reactions
anabolism – „biosynthetic metabolism“
– utilisation of the available substrates for synthesis
(glycogen, structural proteins, hormones, enzymes, bone tissue, etc.)
– energy is consumed in synthetic reactions
- anabolism and catabolism occur continuously in changing proportion
- depending on which processess prevail, the body is in
- catabolic state (fasting)
- anabolic state (food intake)
metabolism – life sustaining reactions
functions of the human body – require continuous supply of energy:
synthesis of tissues, hormones, muscle contraction, active membrane transport, etc.
Metabolic rate- is the amount of energy utilized (released) in the body
- usually expressed in kJ/ 24 hours (1 hour, 1 min)
Units
• Joule (J)
• calorie (cal) – old, but still commonly used unit
• 1 cal = 4,18 J
• 1Cal = 1000 cal
Energetics and metabolic rate
- metabolic rate in a moderately active person: approx. 8 000 -10 000 kJ
- the metabolic rate of individual tissues and organs differs
- high metabolic activity: brain, liver, skeletal muscle
http://www.nature.com/ijo/journal/v34/n2s/fig_tab/ijo2010234f6.html
- lowest metabolic rate required for the maintenance of vital body functions in
basal conditions
- metabolic rate in a person who is awake and who is in basal conditions
- basal conditions:
1. the person is awake
2. physical rest - lying position
3. emotional rest – elimination of emotional excitement
4. normal body temperature (~ 36-37 °C)
5. neutral temperature of the environment (~ 20 - 23 °C)
6. fasting state
(after fat- or carbohydrate-rich meal 12 hours, protein-rich meal 18 hours)
- basal conditions in real life - only just after we wake up
Basal metabolic rate (BMR)
Main factors explaining the differences in BMR
1. Age
2. Composition and size od the body
3. Gender
4. Hormones
5. Genes
Age
- increasing age - the metabolic rate decreases
- the highest metabolic rate (per 1 kg of body weight) is in children (growth)
- in aging – the body composition is changed – less lean tissue, more fat
Body size and body composition
- the larger the body size (kg, cm), the higher metabolic rate
Body surface
- the best indicator for estimation of the BMR (better than weight or height)
- directly related to the metabolic rate
Explanation
- larger body size – more heat is lost (through the skin)
- for thermic homeostasis - more heat (energy) needs to be released
- source of heat - metabolism
• Body composition:
- metabolic rate depends on the proportion of fat fre mass/fat mass
- fat mas - lower metabolic rate
- fat free mass - higer metabolic rate
Gender
- males – higher BMR than females (approx. by 10%)
Causes:
• body composition of males (vs. females)
- lower body fat content (metabolically less active)
- more muscles (metabolically more active)
• larger body size
• higher concentration of testosterone
(anabolic effect)
Hormones
- thyroid hormones T3, T4 (main role in metabolism regulation)
- catecholamines
- growth hormone
- testosterone
E.g.
Stress – epinephrine – higher metabolic rate
Adaptation to cold climate – higher thyroxine production – elevated BMR
Adaptation to hot climate – lower thyroxine production – decreased BMR
Testosterone – higher BMR in males than in females
Genes
- fast vs slow metabolism
depends on
- heat/chemical energy ratio
basal conditions, basal metabolic rate
- it is difficult to keep the basal conditions, since
the measurements require
- time delay from the last meal
- optimum room temperature
- physical rest in lying position
resting metabolic rate (RMR)
- fasting
- physical rest (lying 30 min priot to measurement)
- no stressful stimuli (loud music, shinig light, alcohol, caffeine, exercise)
- by approx. 10 % higher than BMR
- commonly used as a substitute for BMR
1. calculation by formula
e.g. BMR = 293 . body weight (kg) 0,75
2. determination from tables (Harris – Benedict tables)
- data needed: weight, height, gender, age
- read values of BMR from two tables
Value A – depending on age and height
Value B – depending on weight
BMR = Value A + Value B
3. direct calorimetry
- heat released from the body is measured
and recalculated to total energy expenditure
- measurement is performed in special
insulated chambers
- precise, but expensive method, time costly
Measurement of metabolic rate
4. Indirect calorimetry
principle:
- metabolic rate is calculated indirectly
- utilization of O2 and production of CO2 is measured
and based on their values BMR is calculated
Rationale of the method
- human metabolism is aerobic -energy is released by oxidation of substrates
- O2 consumption (and CO2 production) and metabolic rate are directly associated
A/ Closed method - calculation of energy expenditure is based on measurement of
the consumed O2
B/ Open method - calculation of energy expenditure is based on measurement of
both the consumed O2 and produced CO2 (more accurate method)
Determine the basal metabolic rate
a/ by using the Harris – Benedict tables
b/ by indirect calorimetry (open method)
c/ compare the results derived by both mehods
Task. Determination of BMR
Harris – Benedict tables – tables for estimation of BMR/24 h
account for sex, age, weight and height of the subject
include 2 tables for males and 2 tables for females1. value of BMR depending on height and age
2. value of BMR depending on weight
Task
Estimate your BMR using the Harris-Benedict tables
Procedure
- read value 1 from the table for height and age (appropriate for your sex)
- read value 2 from the table for weight (appropriate for your sex)
BMR = value 1 + value 2 (kJ /24 h or kcal/24 h)
Result: BMR=
Conclusion:
Estimation of BMR by Harris-Benedict tables
Task: determine the BMR (24 h) of a volunteer by the open indirect calorimetry
* it is impossible to keep basal conditions in practicals - in fact the resting metabolic rate is measured
Procedure
- the volunteer is lying on a bed
- his/her nose is clipped, he/she is breathing by mouth through a tube with valve
- inspiration – air from atmosphere
- expiration – the expired air is collected in a Douglas bag
- after 10 minutes the measurement is stopped, the bag is closed
- the BMR/ 24 h is calculated by a series of calculations
Task. Measurement of BMR by indirect calorimetry
Measurements
- a sample of exspired air from Douglas bag is taken (1 litre)
- the sample is analyzed on Spirolyt, measured is:
- consumption of O2 (D O2 ) = O2 decrease
- production of CO2 (D CO2 ) = CO2 increase
-the volume of expired air V10 (L) is measured
!!! do not forget to add 1 litre taken for analysis !!!
Values needed for calculations:
- time of the experimenet: 10 min
- volume of ventilated air
− D O2 = O2 consumption (%)
- CO2 production (D CO2 )
-Douglas bag
Calculations
1 Volume of air in 10 min V10 (L)
2 Volume of oxygen in 10 min V10 x D O2 % (L)
i.e. the result from step (1) multiply by % of consumed oxygen
(e.g. x 3,5% is the same as x 0,035)
3 Volume of oxygen in 1 min (V10 x D O2 %) : 10 (L)i.e. the result from step (2) divide by 10
4 Volume of oxygen in 24 h (=1440 min) ((V10 x D O2 %) : 10) x 1440
-i.e. the result from step (3) multiply by 1440
5 Read the temerature in the room (C)
6 Read the atmospheric pressure in the room
7 Find the STPD factor (tables)
8 Adjust the volume of oxygen for the STPD conditions
= (result 4) x STPD = volume of oxygen consumed in 24 h (L)
STPD (standard temperature pressure dry) – the value serves for
conversion of the oxygen consumption
respiratory quotient (RQ) informs what type of fuel is utilized
9. Calculate the respiratory quotient
RQ =
carbohydrates RQ = 1 C6H12O6 + 6 O2 ➔ 6 CO2 + 6 H2O
fats RQ = 0,7 C15H31COOH + 23 O2 ➔ 16 CO2 + 16 H2O
proteins RQ = 0,8
mean value on mixed diet (metabolic mixture) RQ = 0,82
produced CO2–––––––––––––utilized O2
Calculations – cont.
- principle of the method: in oxidation (i.e. consumption of O2) energy is released
- amount of released energy depends on the fuel that is utilised
8. Find the value of energy equivalent (tables)
Energy equivalent (EE)
– value derived from RQ – can be found in a table
- is the amount of energy liberated while using 1 l of oxygen
– i.e. it depends on the type of oxidized fuel (protein, fat, carbohydrate)
– oxidation of 1 mole of different nutrients requires different quantity of O2 and CO2
production is also different
9. BMR = O2 utilization STPD (24 h) . energy equivalent
Conclusion:
Compare the value of BMR estimated from tables and assessed by calorimetry.
Explain which value do you consider more precise.
Main components of daily energy expenditure
Basal metabolic rate
(60%)Sleeping
metabolic
rate
Arousal
Physical activity 25 – 30% (or more)
Thermogenesis (7 – 15%)diet induced + adaptive
physical activity
- major effect on metabolic rate – causes majore increase
-light physical activity 1,7 x BMR
-medium physical activity 2,4 x BMR
-vigorous activity 3,3 x BMR (up to 6x BMR)
specific – dynamic action of food
= extra energy needed for digestion, absorption, storage of nutrients
- carbohydrates: increase of BMR by 5 –10 %, fat + 4%, effects last ~ 3-12 hrs
- proteins: increase of BMR by +30 %, lasts for ~18 hrs
- typical food (mixture of protein, fat, carbohydrates) increase by 6 % (~ 12 hrs)
temeprature of surrounding environment, climate
- temperature above or below 20-23 °C
body temperature
- increase of temperature by o 1°C – increase of metabolic
rate by ~ 10 % and vice versa
other factors – drugs, pregnancy, caffeine, etc.
Factors that increase the metabolic rate:
1. physical activity
- major factor that increases the metabolic rate
- the increase depends on intensity of the
physical activity
(mild – moderate – vigorous)
Factors that increase the metabolic rate
- strenous exercise – dramatically increases metabolic rate
- major factor contributing to the energy balance between E intake – E expenditure
Activity Increase of
BMR
Sitting activities (eating, computer games, studying) 1.4
Standing activities - light (washing dishes, cooking) 1.7
Walking slowly (a walk) 2.8
Walking at normal pace 3.2
Walking fast 3.4
Sport – light physical activity (bowling, table tennis. etc.) 3.3
Sport – medium physical activity (swimming, tennis, skating, aerobic, cycling) 5.5
Sport – heavy (football, athletics, jogging, hockey) 6.6
BMR
Physical
activity
Thermogenesis
BMR
Physical
activity
Thermogenesis
Sedentary Physically active
Obesity
– major health problem
Weight loss
= to get rid of fat (body energy stores)
physical activity – the main factor to increase the energy expenditure and to
spend more energy
currently – many people are sedentary tendency to gain weight
- indication of a person´s physical activity by a single number
- is the ratio between the total daily energy expenditure and 24-hour basal
metabolic rate
PAL =
-for adults, a PAL above 1.75 is considered to be compatible with a healthy lifestyle
PAL – Physical activity level
energy expenditure in 24 h___________________________basal metabolic rate
PAL Daily Activities Lifestyle
< 1.4 Hospital patient with limited physical mobility Inactive
1.4 - 1.69 Little physical activity at work or in leisure time, e.g. office worker Sedentary
1.7 - 2.0 Moderate physical activity at work, e.g. in construction, or some jobs
in agriculture or the leisure industry.
Office workers who work-out e.g. in gym for an 1 h/ day.
Moderately
Active
2.0 - 2.4 Considerable physical activity at work, e.g. outdoor occupations,
fitness trainers who run alongside clients. Office workers who take at
least moderate exercise for two or more hours/day.
Very
Active
> 2.4 Professional athlete or sports person Extremely
Active
Task. Calculation of the daily energy expenditure from tables
• metabolic rate during any activity (standing, washing dishes, running, etc.)
can be expressed as multiple of BMR
• the multiple (coefficient) indicates, how many times the BMR is
increased during particular activity
– e.g. fast walking c=3,4
– i.e. during fast walking the metabolism is increased 3,4x
– i.e. energy expenditure during fast walking is 3,4 x BMR
Task
• calculate your metabolic rate in the previous day (24 hours) by using
the tables
Principle
• 1-day metabolic rate is calculated as sum of energy expenditures
during individual daily activities (sleeping, waking up, breakfast, walking to
school, sitting on a lecture...)
• calculate your 24 h basal metabolic rate (BMR) by tables
• calculate your 1 minute BMR (BMR1min = BMR24 h : 1440)
• make a table into your notebook:
• into the table write a list of all your activities during 24 - hours
(from the time you woke up until the same time next day, sum = 1440 min)
• write duration of all activities in minutes
from – to: ...............= minutes
• in tables find the appropriate activity and its coefficient (c)
– c indicates how many times the BMR increases during the activity
– if activity you have done is not included in the tables, find a similar one
Activity from to duration in
minutes coefficient BM1min x duration of activity x c
Sum 1440
• energy expenditure during each activity is calculated in the following way
duration of the activity in minutes x c x BMR1min
• energy expenditure per 24-h is calculated as sum of all partial energyexpenditures
• calculate your physical activity level (PAL)
PAL = EE per 24 h : BMR per 24 h
• Conclusion: evaluate your physical activity level during the previous day(use the tables)
Activity from to duration in
minutes coefficient BM1min x duration of activity x c
Sum 1440