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