2. Basal Metabolic Rate (BMR)

3. Basal Metabolic Rate OR
Sustain vital functions like those of heart, circulation brain, lungs and cellular functions. OR
It is the minimum amount of energy required to maintain life,
Energy required by an awake person during physical, emotional and digestive rest.
BMR of a sleeping person is lower than awake person.

4. HOW IS BMR MEASURED
1. Directly by the heat evolved.
2. Indirectly by the volume of Oxygen consumed and CO2 evolved / unit time.

5. Open Circuit Method
O2 consumption and CO2 production both are measured
Highly technical
Less rapid
More accurate
Tissot method, Douglas method of BMR are open circuit

6. BMR Measurement Benedict-Roth closed circuit method
Pre-requisites
Person should be awake
Physically & mentally at rest
Should have not consumed any food during preceding hours (post absorptive)
Surrounding temp should be about 25oC

7. Closed Circuit Method In clinical practice this method is used
Sufficiently accurate
O2 consumption is measured
Rapid, as 2-6 minutes are spent under basal conditions.
O2 consumption is measured in a closed circuit system
Benedict Roth Metabolism apparatus is used.

9. Benedict Roth Metabolism apparatus

12. Apparatus consists of:
A cylindrical spirometer vessel closed at upper end which floates on a water jacket below to make an air tight water seal.
Spirometer is filled with O2 & is connected by passages regulated by valves.
Outlet passage connected directly to mouth piece.
Inlet passage is connected to soda-lime container to absorb CO2.

13. Procedure Subject kept under basal condition Tube is Inserted in mouth
Nostrils are closed
Breathing through mouth
Test in run for 2-6 minutes
Movements are recorded manually / electronically
Volume of O2 consumed is noted
Corrections to standard conditions are made (Temperature and Barometric pressure)

14. Calculation O2 consumption is multiplied by 10 to convert to hour
Multiplied by C, heat production represented by each liter of O2 consumed
This gives heat production in C/hour
As BMR is to be expressed as C/hour/Sq m, the energy output/hour obtained has to be divided by surface area of the subject.

15. Calculation of Surface Area
MTC x 2 x height = Surface area in Sq cm (Cm) (Cm)
DU Bois formula:
A = H x W x Sq cm
Cm kg
A = H0.725 x W x Sq m
Surface area of an average adult is about 1.8 Sq meter

16. Example: Calculation of BMR
Age = 35 years
Weight = 70 kg
Height = 170 cm
O2 Cons = 1.2 liters/6min
Corrected = 1.2 x 10 = 12 liters/hour
Energy output / Heat produce = 12 x = 58 C/hour
Surface area = 1.8 Sq meter
 BMR = 58C = 32 C/hour
Normal for this person = 39.5 C/hour/Sq meter

17. Scale based on body weight & height have been developed & can be used
for calculating
Body Surface Area
Nomogram

18. Determination of BMR by Read’s Formula
BMR = 0.75 (PR) x (PP) – 72
PR = Pulse rate
PP = Pulse pressure
It gives BMR correct within ± 10% of the normal

19. Normal BMR Adult men = 34-37 kcal/hr/Sq m
Adult women = kcal/hr/Sq m
For day to day calculation
Males = 24 kcal/kg body wt/day
According to International Commission on Met. Rate the BMR of SE Asian people is a little lower than European

20. Basal Metabolism Conditions:
Energy requirement varies with PAL & environmental conditions
Energy production = More or less the same under standard condition known as “Basal Metabolism”
Conditions:
Awake but complete rest – Physical / mental
Fasting at least 12 – 18 hours – Post absorption state

21. Basal Metabolism Postabsorptive state allowed to avoid
Effect of digestion and absorption
Effect of SDA of food stuff
Prevent any chance of starvation
3. Recumbent / reclining position
4. Remain in normal living condition
Temperature, Pressure & Humidity

22. Basal Metabolism
Under these conditions the energy expenditure is only on:
Respiration
Circulation
Muscle tone (skeletal and smooth muscles)
Functions of viscera (kidney, liver & Brain)

23. Amount of heat given off by a subject who though awake is lying in a state of maximum physical and mental rest under comfortable condition of temperature , pressure ,humidity and hours post-absorptive state.

24. Significance of BMR BMR helps in the assessment of thyroid function.
It helps in the calculation of daily energy requirement of a person.
It helps in planning diet for an individual.
It also helps in the differential diagnosis of leukemias , polycythemia , addison’s disease.

25. Factors Affecting BMR

26. The rate of metabolism at "basal" conditions has been found to vary in different individuals due to different factors.

27. Age In period of active growth BMR is high.
The BMR of children is much higher than adults
Reaches maximum by 5 years
Is low in old age
Roughly speaking it is inversely proportional to the age

28. BMR Variation with Age Age BMR kcal Upto 6 years 57.5 12 50.4 20 40 3038
38.5 70
35.5

29. Sex Women normally have a lower BMR than men.
BMR of females decline between the ages of 5 and 17 more rapidly than those of males.

30. Environmental Temperature
In cold climate BMR is a compensatory mechanism to maintain body temperature

31. Fever BMR is high in febrile state
12% rise is found associated with 1oC rise in temp

32. Racial variations
When the BMR of different racial groups is compared, certain variations are noted
BMR of adult Chinese is equal to or below the lower limit of normal for westerns.
BMR of oriental (Eastern countries) female students living in USA is on an average 10% below the standard BMR for American women of the same age-groups.
High values 33% above normal have been reported in Eskimos.

33. State of Nutrition
BMR is low in conditions of mal nutrition, starvation and wasting diseases.

34. Barometric Pressure
Moderate reduction of atmospheric pressure does not affect the BMR, but a fall of pressure to ½ an atmosphere (viz. O2 tension 75 mm Hg), as occurs in mountain climbing increases BMR, but increased pressure of O2 does not raise BMR.

35. Profession
Athletes, Soldiers and Manual workers have a slight higher BMR than persons leading a sedentary life

36. Drugs Quite a number of drugs like Caffeine, Benzedrine Epinephrine,
Nicotine,
Alcohol, etc. increase the BMR
Reverse is observed with most of the anesthetics

37. Hormones
Circulating levels of hormones secreted by thyroid, adrenal medulla and anterior pituitary increase BMR
The Stimulant effect on rate of metabolism and Heat production.
BMR raised in Hyperthyroidism
BMR Low in Hypothyroidism
One mg of thyroxin increases BMR by about 1000 C..

38. Thyrotoxicosis
BMR may increase by 50 to 100% above normal, but RQ remains unaltered since both 02 consumption and CO2 production increase proportionately in such cases

39. Myxoedema BMR is diminished to 30% or even 45% below normal.
Anterior pituitary through its TSH affects BMR
Growth Hormone. also causes about 20% rise in BMR,
catecholamine increase BMR by about 20% of the resting value.
Male sex hormones cause a 10% increase in BMR.

40. IMPORTANT TO NOTE
As all other factors are taken care of in the definition of BMR, therefore thyroid function determines the changes in BMR

41. Pregnancy
The BMR of pregnant mother after six months of gestation rises.
It may be noted in pregnancy that the BMR of the mother is the sum total of her own metabolism as in her non-pregnant state and Combined with that of the fetus hence pregnancy exerts no specific effect upon BMR.

42. THANKS

43. CLINICAL ASPECT: Pathological Variations in BMR 1. Fever:
Infections and febrile diseases elevate the BMR, usually in proportion to the increase in temperature

44. Diseases
Characterized by increased activity of cells which also increase heat production due to increased cellular activity. Thus, BMR may increase in such diseases as:
Leukaemias (21 to 80%)
Polycythemia (10 to 40%)
Some types of anaemias,
Cardiac failure, (25-80%)
Hyper­tension and
Dyspnoea
All of which involve increased cellular activity

45. Endocrine diseases
The most important factor which alters BMR is the state of function of thyroid.
In fact, determination of BMR is mainly used for the assessment of thyroid function.

46. Endocrine diseases
In hyperthyroidism, BMR is increased to + 75% or more.
In hypothyroidism (myxoedema), BMR is reduced to 40% or more.
BMR is also increased in Cushing's disease and Cushing's syndrome and also in Acromegaly.
BMR is decreased in Addison's disease (Hypo­function of Adrenal cortex

47. Importance of BMR
As a diagnostic aid: For the diagnosis of various pathological conditions specially assessing the thyroid function (specially useful where hormone assays and isotope laboratory is not available).

48. For calculation of caloric requirements
Essential in the calculation of calorie requirements of an individual for prescribing a diet of adequate calorific value and planning nutrition for individuals as well as communities and populations at large.

49. Specific dynamic action and physical activity levels are the important attributes of Basal Energy Expenditure.

50. Specific Dynamic Action
Also known as thermogenic effect of food.
Increased heat production following the intake of food.
Energy expenditure on digestion and absorption.
Trapped from energy stores
Actual energy from food is less than theoretical content
Activation energy needed for a chemical reaction and is to be supplied initially

51. EXAMPLE A person takes 250 grams of carbohydrates
Should produce 250 x =1000 Kcal
10% needed for activation = 100 kcal
Actual energy available = 900 Kcal
If requirement is really =1000 Kcal
Then the person should actually take an amount capable of providing 1100 Kcal i.e. 275 grams

52. SDA Values
Carbohydrates %
Protiens %
Fats %
Mixed Diet %

53. Physical Activity Level (PAL)
Energy required in kcal/hour
(over and above BMR)
1. Eating 28
2. Writing 30
3. Driving a car 63
4. Typing at high speed
100
5. Walking
140
6. Cycling
175
7. Running
490
8. Swimming
550

54. Energy Requirement and Occupation
Type of activity
Occupation
Light
Sedentary Work
Office workers, lawyers, accountants, doctors, teachers, architects, shop workers
Moderate
Moderate Work
Students, industry workers, farm workers, housewives without mechanical appliances
Very active
Heavy Work
Agricultural workers, miners, unskilled laborers, athletes, factory workers
Very Heavy Work
Lumber jacks, blacksmiths, and construction workers
BMR+30 %
BMR+40 %
BMR +50%
BMR+70 %

55. Calculation for energy requirement for a 55 kg person doing moderate work
For BMR = 24 x 55 kg = 1320 kcal
+ For activity = 40% of BMR = 528 kcal
Subtotal = = 1848 kcal
+ Need for SDA = 1848 x 10% = 185 kcal
Total = = 2033 kcal
Round to nearest multiple of 50 = 2050 kcal

56. Proximate Principles Carbohydrates Fat Proteins Minerals Vitamins
Additional requirements for growth pregnancy lactation and convalescence are to be provided in the food.

57. Respiratory Quotient
When food is oxidized, whether in an open system or closed biological system, oxygen is consumed and CO2 produced.
Volume of CO2 produced
Volume of O2 consumed
= RQ
Ratio in steady state / Unit time

58. Carbohydrates are completely oxidized and the volume of O2 used is equal to CO2 produced
C6H12O6 + 6O2  6CO2 + 6H2O
RQ =
6CO2
6O2
= 1

59. Fats
C57H104O O2  57 CO H2O
RQ = 57 = 0.71 80
Other fats have RQ  0.70

60. Using specialized technique the RQ is found to be 0.82
Proteins
RQ of proteins is a little complex to determine as it contain N & S in addition to C, H, O.
Using specialized technique the RQ is found to be

61. Alcohol
C2O5OH + 3O2  2CO2 + 3H2O
RQ = 2/3 = 0.67

62. Human Use normally mix type of food
RQ of an intact person naturally will be the sum of RQ of all the three major type of food.
Carbohydrates
Fats
Proteins

63. Ordinary mixed diet RQ = 0.85
Postabsorptive State
No food being consumed in preceding – 14 hours
RQ = 0.82

64. When diet is rich in Carbohydrates the RQ will be more close to one i
When diet is rich in Carbohydrates the RQ will be more close to one i.e. High
More fats = Lower RQ

65. Methods for determination of RQ of Man
Two method
Open Circuit
Closed Circuit

66. Open Circuit
Made to breath in a specially designed bag called Douglas Bag for few minutes
Volume of Breathed air is measured in a gasometer
Subjected to gas analyzer
Where CO2 is absorbed by KOH
Original volume of gas is reduced

67. Open Circuit Concentration of CO2 is calculated
Remaining gas is allowed to react with alkaline pyrogalate which absorb O2
O2 in the expired is found out
RQ is calculated volume of CO2
volume of O2

68. Remember that when rate of utilization of
fat increases in relation to carbohydrates, RQ falls.
Commonly seen in Diabetes mellitus
Utilization of carbohydrates increases RQ

69. Energy requirement of a normal person
While calculating we should consider the energy required for
Maintenance of BMR
Thermogenic effect of food (SDA)
Extra energy expenditure for PA