A lucid presentation on Respiratory Quotient (RQ) of Nutrients for medical ,dental ,pharmacology and Biotechnology students for easy-learning.

1. Respiratory Quotient (RQ) of Nutrients
Dr. Rohini C Sane

2. Respiratory Quotient(RQ)
• Respiratory Quotient(RQ) : is defined as the ratio of volume of CO2
produced (eliminated) in L/g by volume of oxygen consumed (utilised)
in L/g during oxidation of food stuffs during a given time.
• Fats have relatively lower RQ than carbohydrates because the oxygen
content of fats is less than CO2 content and therefore , more oxygen
from outside is required for oxidation.
• Respiratory Quotient decreases with increase in rate of utilisation of
lipids in relation to carbohydrates. RQ is lowered if carbohydrate
metabolism is impaired. e.g. Diabetes Mellitus.
Nutrient Respiratory quotient
Carbohydrate 1.0
Lipids 0.7
Proteins 0.8
Mixed diet 0.82- 0.85(variable)

3. • C6H1206+ 6O2 6CO2 +6H2O
Respiratory Quotient(RQ) of carbohydrate=CO2/O2 = 6/6 =1
• C57H110O6+163 O2 114 CO2+110 H2O(Triesterin)
Respiratory Quotient(RQ) of lipid =CO2/O2 =114/163 =0.7
• Respiratory Quotient(RQ) of proteins = 0.8 (no special formula ,
indirect measurements). RQ of proteins is variable as the chemical
structure of proteins is highly variable .
• Respiratory Quotient(RQ) of the mixed diet (normally ingested)=0.8
• (RQ) of lipid< (RQ) of carbohydrate because of low oxygen content in
a lipid molecule,more O2 from outside is required for oxidation of
lipids.
Respiratory Quotient(RQ) of Nutrients

4. • C6H1206+ 6O2 6CO2 +6H2O
Respiratory Quotient(RQ) of carbohydrate=CO2/O2 = 6/6 =1
• C57H110O6+163 O2 114 CO2+110 H2O(Triesterin)
Respiratory Quotient(RQ) of lipid =CO2/O2 =114/163 =0.7
• Respiratory Quotient(RQ) of proteins = 0.8 (no special formula ,
indirect measurements). RQ of proteins is variable as the chemical
structure of proteins is highly variable .
• Respiratory Quotient(RQ) of the mixed diet (normally ingested)=0.8
• (RQ) of lipid< (RQ) of carbohydrate because of low oxygen content in
a lipid molecule,more O2 from outside is required for oxidation of
lipids.
Respiratory Quotient(RQ) of Nutrients
Respiratory Quotient(RQ) of Nutrients
RQ is simply a ratio . It gives no idea as to the absolute quantity of gaseous
exchange.
Proportional increase or diminution of CO2 produced and O2 consumed will keep
ratio unchanged .
But any disproportionate variation will be reflected by a corresponding change in
the RQ.
Nutrient O2 consumed L/g CO2 produced L/g RQ
Energy yield
kJ/L of O2
Carbohydrate 0.829 0.829 1 20
Lipid 2.016 1.427 0.71 20
Protein 0.966 0.782 0.81 20
Alcohol 1.429 0.966 0.66 20

5. It is done by measuring the volume of O2 consumed and
CO2 produced during a given time with the help of
Douglas bag or other similar instruments.
Method of determination of Respiratory Quotient

6. Clinical applications of Respiratory Quotient (RQ)
• RQ
1. increases in acidosis since CO2 output is greater than O2 consumption during
acidosis.
2. decreases in alkalosis since CO2 output is reduced as respiration is
depressed during alkalosis.
3. increases in febrile conditions as body temperature rises due to high grade
fever resulting in increased breathing and CO2 production.
4. decreases in starvation due to oxidation of stored glycogen and triacylglycerols.
5. falls in diabetes mellitus as carbohydrate oxidation is reduced and fat
oxidation is increased.
6. is lowest when ketolysis is active. Respiratory quotient decreases when fat
utilisation increases with respect to carbohydrate .
7. increases on insulin administration as carbohydrate oxidation elevated with
insulin administration.

7. Significance of Respiratory Quotient(RQ)
• RQ
1. helps in the determination of metabolic rate.
2. is guide for assessing the type of burning or the nature
of synthesis taking place in whole body or in any
particular organ.
3. aids in diagnosis of acidosis, alkalosis and diabetes
mellitus.
4. Non- protein RQ is used for calculating the total energy
output and the proportions of various foodstuffs being
burnt.

8. Energy compounds preferred by Organs
Tissue
energy compounds preferably
utilised
energy compounds
exported
Liver Amino acids ,Glucose ,Fatty acids Glucose ,Fatty acids
Adipose tissue Fatty acids Fatty acids ,Glycerol
Skeletal muscles Glucose ,Fatty acids Fatty acids ,Glycerol
Brain Glucose , Ketone bodies None

9. Total heat production
Heat production= grams of food stuff oxidised x caloric
value of that food
Total heat production= sum of caloric values of nutrient
ingested
Type of
nutrient
ingested
grams food
stuff oxidised
calorific
value
(kcal/g)
calculation
of heat
produced
heat production
(kcal)
Carbohydrate 210.7 4 210.7x4= 842.8
Lipid 84.4 9 84.4x 9= 759.6
Protein 80.0 4 80.0x4= 320
Total heat production=1922.4 kcal

10. Energy source in the main storage tissue
Energy source Main storage tissue Weight( kg)
Energy equivalent
(kcal)
Triglycerol Adipose tissue 15 135000
Protein Muscle 6 24
Glycogen Muscle, Liver 0.2 800

11. 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.

12. Fuel demand
BMR: Basal metabolic rate
SDA: Specific dynamic action
BMR SDA Physical activity Additional energy
supply:Growth,
Pregnancy,
Lactation
Fuel demand

13. Thank You