A lucid presentation on Basal metabolic rate ( BMR) and nutrition for medical ,dental ,pharmacology and biotechnology students to facilitate easy-learning.
2. Energy requirements of a normal person
A. To maintain Basal metabolic rate( BMR)
B. Specific dynamic action (SDA)or thermogenic effect of food
C. Extra energy expenditure for physical activities
D. Efficiency of conversion to ATP = 40%
E. At rest conversion to heat
F. Energy density = energy yield / unit weight of food
All above factors have to be considered while calculating the
energy requirements of a normal person.
4. Basal functions
• Working of heart , brain and other organs
• Blood circulation
• Respiration
• Conduction of nerve impulse
• skeletal and smooth muscle tone
• Gastrointestinal motility
• Reabsorption by renal tubules
• Ion transport across the membranes(50% basal energy
consumed for sodium potassium pump)
5. Basal metabolic rate(BMR)
Basal metabolic rate(BMR): is the minimum energy required by an
awaken individual (body) to maintain life during complete physical ,
emotional(mental) and digestive (post absorptive= 12 hours after last
meal) rest.
BMR is the minimum amount of energy required/produced to
maintain life or sustain vital / basal functions per unit time (one hour).
It is the lowest level of energy production that is compatible with life.
Resting metabolic rate (RMR): is the measure of energy required to
maintain life or vital functions.
Resting metabolic rate (RMR)is 3% higher than the Basal metabolic
rate(BMR).
• Metabolic rate during sleep < BMR
6. Preparation of a subject for measurement of Basal metabolic rate(BMR)
• During test a subject should be :
A. in awaken state in reclining / recumbent position on bed
B. at complete physical and mental rest/relaxaton
C. in post-absorptive state (12 hr. fasting)
D. in comfortable surroundings(at 25 0
C,normal humidity and
pressure)
The subject is asked to breath through a mouth piece for 6
minutes.The oxygen present in the cylinder is utilised by the
subject during this time.
The volume of oxygen consumed by a subject is recorded.
7. Apparatus for measurement of Basal metabolic rate(BMR)
• Benedict-Roth basal metabolism apparatus (closed circuit
device /method): is more accurate ,direct and frequently
used method . This the apparatus allows not only heat
measurement ,but the O2 absorption and CO2 output can be
determined.
• Douglas bag method (open circuit method): in which both
O2 consumption and CO2 output are measured. It is slow
and cumbersome method .
8. Procedure for Measurement of BMR using Atwater-Benedict-
Roth basal metabolism apparatus
1. awaken state in reclining /recumbent position on bed during test
2. no physical activity
3. at mental rest /relaxation
4. comfortable surroundings (at temperature 25 0
C,normal humidity and
pressure)
5. in post-absorptive state (12 hr. fasting)
6. The person breaths in oxygen from a metal cylinder using a mouth
piece. Volume of oxygen consumed by a subject is measured for 2-6
minutes and recorded on a graph paper.
7. CO2 produced is absorbed and measured using soda lime.
All these conditions ensure
energy output of the individual
to maintain basal functions and
body temperature.
9. Measurement of body surface area by formula of Eugene DuBois and
Del afield DuBois (1915)
A= W 0.425 x H0.725 x 71.84
• A= surface area in cm2,W= body weight in kg ,H=height in cm
• Nomograms of body surface area (directly in m2)are
readily available for heights ,weights.
H=height in cm W= body weight in kg A= surface area in m2
75 15 0.52
150 40 1.3
180 80 2.00
10. Measurement of Basal metabolic rate(BMR):1
• Standard calorific value for one litre of O2 consumed/utilised
= 4.825 kcal heat generated or produced .
• Volume of oxygen consumed in litres for 2-6 minutes = (X)
• Heat produced in 6 minutes = (X)x 4.825 kcal
• Heat produced in 24 hrs in kilocalories = (X)x 4.825 kcal
x24x10
• Units of BMR: kcal /hr/square metre body surface area=
kcal/hr/ Square metres (m2)
• Square centimetre(cm2 )=Square metres (m2)/10,000
11. Measurement of Basal metabolic rate(BMR):2
Measurement of Basal metabolic rate(BMR)=
Volume of Oxygen(O2) consumed
Volume of CO2 evolved per unit time
• Atwater-Benedict-Roth basal metabolism apparatus (closed
circuit device /method) is used for the measurement of BMR.
• BMR = Kilocalories of heat evolved per hour/square meter of
body surface
• Measurement of body surface area by formula of Eugene
DuBois and Del afield DuBois 1915)
A= W 0.425 x H0.725 x 71.84
A= surface area in cm2,W= body weight in kg ,H=height in cm
The BMR is calculated from the values of oxygen consumption ,
calorific value and surface area.
12. Normal values of Basal metabolic rate(BMR)
Normal values of BMR for an adult man = 34-37 kcal/ m2 / hr
Normal values of BMR for an adult man = 1600 kcal/day
Normal values of BMR for an adult woman= 30-35kcal / m2 / hr
Normal values of BMR for an adult woman= 1400 kcal /day
Normal values of BMR for an adult: 24 kcal/kg body weight /day
BMR value between between -15% and +20% is normal.
BMR (Indian) < BMR (European)
13. Indirect Calorimetry
• Indirect Calorimetry(Nahan Lipson):
H2 (deuterium)+ O18 (labelled oxygen) H2 O (Labelled water)
1. Elimination of Deuterium Labelled water with H2 O
2. Elimination of Oxygen CO2 and H2O
• Elimination of CO2 = Elimination of Oxygen- Elimination of Deuterium
• Elimination of CO2 =2-1
• Double labeled H2O method (Nahan Lipson) provides a measure of
total CO2 production over 2-3 weeks.
• The method is useful to measure alterations in energy requirements
during growth ,pregnancy and lactation.
14. Factors affecting Basal metabolic rate(BMR):1
1. Age : BMR is low in newborns and in children it is higher during active
growth. In old age BMR is lowered. Per decade 2% decrease in BMR.
2. Sex:BMR of males (due to 5% higher lean muscle mass) > BMR of females.
3. Surface area :BMR directly proportional to Surface area (Surface area
directly proportional to height and weight) .Lean have greater surface area
therefore higher BMR.Obese lesser surface area therefore lower BMR.
4. Environmental temperature:BMR is higher in cold climates (winter) .
BMR is lower in warm climates(summer).It is a compensatory mechanism to
maintain body temperature .
5. Physical activity (exercise): increases BMR as physical exercise
increases cardiac output . Increase in surface area(Athletes) and regular
exercises increases BMR.
6. Nutritional state : BMR is low starvation and malnutrition . BMR has
inverse relation with the energy intake . It decreases up to 50% as a an
adaptation by the body during the period of starvation.
BMR of strict vegetarians < non-vegetarian-meat eaters (11% higher)
15. Factors affecting Basal metabolic rate(BMR):2
7. Hormones :Thyroid hormone (T3 and T4): play role in maintaining BMR. They
have stimulatory effect on rate of metabolism and heat production.
Hyperthyroidism / thyrotoxicosis : BMR increases(70%) , Hypothyroidism /
myxoedema : BMR decreases (40%).
Epinephrine/ Cortisol / sex hormones /growth hormones /Thyroid hormones :
increase BMR. BMR was used to assess Thyroid functions.
8. Racial variation:Eskimos have higher BMR .BMR of Oriental women living in
USA is 10% lower than the average BMR of American women of same age group .
9. Disease states : elevated BMR in leukemias / Polycythemia / cardiac failure /
hypertension/dyspnoea/anaemia ( all of diseases involve increased cellular activity) .
In Addison’s disease(adrenal insufficiency) BMR is marginally lowered. In Cushing’s
syndrome /Acromegaly BMR is increased.Fever: infections/ febrile conditions 10%
elevation in BMR per degree centigrade rise in human body temperature .
10. Drugs : caffeine , alcohol, Benzedrine ,nicotine increase BMR.Anaesthetics
decrease BMR.
16. Significance of Basal metabolic rate(BMR)
• BMR helps in calculation of calorie requirements of an individual for
planning of a diet to maintain body weight .
• To observe the effects of types foods and drugs on BMR.
• BMR useful in assessment of Thyroid functions( as a diagnostic tool for
disorders of Thyroid especially where hormone assays not available ).
Conditions associated with increased
BMR
Conditions associated with decreased
BMR
Hyperthyroidism (70% increase) Hypothyroidism(40% Decrease)
Thyrotoxicosis Starvation
Cardiac Failure Myxoedema
Hypertension Addison’s Disease(Adrenal Insufficiency)
Leukemias Lipoid Nephrosis
Polycythemia Undernutrition
Fever/ Infections/Febrile Conditions Hypothalamic Disorders
