Energy balance & metabolic rate. Metabolism means changes , it is used to refer to all chemical and energy transformation processes that occur in the body. It is divided into two processes : 1- anabolism which means formation of proteins, fats, complex
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Energy balance &metabolic rate
It is divided into two processes :
1- anabolism which means formation of proteins, fats, complex
Carbohydrates& high energy compounds from simple molecules
with taking up energy that is stored in these compounds.
2- catabolism which is a complex, slow oxidation of carbohydrates
Fats & proteins which produces CO2, H2O and energy that is liberated in small usable amounts.
Energy transfer :
When pure oxygen is used to burn carbohydrates, fats and proteins outside the body, large amounts of energy are released suddenly in the form of heat. Inside the body, the energy needed by physiological processes is not only heat but :
energy to cause muscle contraction or to do secretion by the glands, these processes take place through special enzymes& energy transfer systems which apply the energy liberated by catabolism to the formation of high energy compounds.
1- high energy phosphate compounds :they include :
Adenosine triphosphate (ATP)
Creatine phosphate (CP)
Guanosine triphosphate (GTP
Cytidine triphosphate (CTP)
Uridine triphosphate (UTP)
Inosine triphosphate (ITP)
2-Acyl-Co A compounds :e.g. Acetyl-Co A which is also called
active acetate .
The main functions of ATP are :to energize the synthesis of cellular compounds, to energize muscle contraction& active transport across membranes, absorption from intestine or kidneys, formation of glandular secretion and maintainance of
Ionic concentration gradient in nerves .
On the other hand, if the energy intake exceeds energy loss,
the balance is positive, and there is weight gain. to be in
energy equilibrium, the energy input must equal the energy
Physical caloric (heat) value of food:
It is the amount of energy in Kcal which is liberated by complete oxidation of a food substance outside the body.
Oxidation of 1 gram of carbohydrates produces 4.1 KCal/gram
Oxidation of 1 gram of fat produces 9.3 KCal/ gram
Oxidation of 1 gram of protein produces 5.3 KCal/ gram
Physiological caloric value of food:
Oxidation of food substances inside the body, it equals:
4.1K Cal/gram of carbohydrate.
9.3 Kcal/ gram of fat.
4.1K Cal/ gram of protein.
The physiologic caloric value of protein is less than its physical
caloric value because protein is incompletely oxidized in the body
To CO2, H2O and urea .
Measurement of physiological heat value is done by using special
Caloric intake (in K Cal)=
Dry weight in grams of carbohydrates ingested X 4
Dry weight in grams of fats ingested X9
Dry weight in grams of proteins ingested X4
The energy liberated by catabolism, appears as external work,
energy storage and heat .
Energy output= external work+ energy storage+ heat .
_ The metabolic rate is the amount of energy liberated per unit oftime.
When no external work is done as during isometric contraction
of skeletal muscles, all of the energy expended by the body is
converted into heat. (this energy was stored as ATP).
Metabolic rate is measured by either direct or indirect calorimetry.
In this method the metabolic rate is determined by measuring the total
quantity of heat liberated from the body in a given time provided that
the person is not performing any external work. The subject is placed
In a large constructed calorimeter, which is an air chamber that is well
Insulated& no heat can leak through its walls. Heat liberated from the
subject's body warms the air of the chamber which is maintained
constant by a cool water bath. The rate of heat gain by H2O bath is
measured by a thermometer, it equals the rate at which heat is liberated
by the subject's body. Direct calorimetry is used only in research centers.
Since most of energy expended in the body is derived from reactions
Which utilizes oxygen, the metabolic rate can be calculated from the rate
Of oxygen consumption.
Energy equivalent of oxygen:
It is the amount of energy liberated per liter of oxygen utilized in the body.
It differs according to the type of metabolized food ,it is greater for carbo-
Hydrates than for fats or proteins. For a mixed diet it equals 4.82 K Cal.
Metabolic rate =O2 consumption per unit of time x 4.82
(in K Cal/unit of time) (in liters)
O2 consumption is usually measured with a metabolator.(an apparatus),it is a
Spirometer filled with oxygen with a CO2 absorbing system.
RQ=volume of CO2 produced
volume of O2 consumed per unit time
RQ could be measured for the whole body or for individual organ or tissue.
Importance of RQ:
1- it idicates the type of food being utilized.
RQ for fat = 102/ 145 = 0.7
RQ for protein = 0.82
After determination of RQ we can find out the oxygen heat value from the
metabolic table then we can calculate the metabolic rate .
Metabolic rate = O2 consumption/hour x O2 heat value
Energy equivalent of oxygen or the energy liberated when one liter of O2
Is used to oxidize food :
for oxidation of carbohydrate = 5 K Cal / L
for oxidation of fat = 4.7 K Cal / L
for oxidation of protein = 4.5 K Cal /L
3-RQ estimation is an evidence for transformation of one food substance into another as in case of transformation of carbohydrates
which is rich in O2 into fat which is poor in O2. : inside the body O2 is
thus released and forms CO2 without any increase in atmospheric O2
Consumption . The RQ is there fore is increased to above 1.
On the other hand, transformation of fat into carbohydrate (gluco neo-
Genesis) , here fats use O2 for transformation to carbohydrates and more O2 to oxidize carbohydrate to CO2 & H2O so :
RQ = CO2 produced from oxidation
O2 consumed for transformation + oxidation
in this case the RQ is below 0.7
RQ O2 heat value in cal. CHO % Fat %
o.7 4.68 0 100
o.85 4.86 50.7 49
0.87 4.88 57.5 42
0.95 4.98 84 16
1 5.04 7 100 0
Metabolic rate = O2 consumption/ hour x O2 heat value
Category Age K Cal./ day
Children 1-3 years 900-1300
4-6 years 1300-2300
7-10 years 1650-3300
Males 15-18 years 2100- 3900
above 67 years 1650- 2450
Females 15-18 years 1200- 3000
above 67 years 1200- 2000
Pregnancy + 300
A male aged 20 years, his height is 168cm. ,body weight is 70 kg. ,
Body surface area is 1.5 m2 :
Suppose O2 consumption in 10 minutes (using respirometer)
2500 ml O2 : 2500 ml / 10 min. 250 ml/ 1 min.
250 x 60 = 15000 ml/ hour = 15 L/ hour
As energy equivalent for 1 L of O2 =4.84 KCal
So energy produced = 15 x 4.84 = 72.6 K Cal/ hour
B.M.R in K Cal /m2/hour =72.6 ÷ 1.5 = 48.4 K Cal /m²/ h.
-The standard value for B.M.R. at age 20 years is 41.4 K Cal/m²/h.
so % excess = 48.4 – 41.4 x 100 = + 16.9 %
Type of activity Calories per hour.
Awaking & lying in bed 77
Sitting at rest 100
Dressing % undressing 118
Typewriting rapidly 140
Walking slowly 200 (2.6 miles/h.)
Active exercise 290
Strenuous exercise 450
Running (5.3 miles/h.) 570
Walking upstairs 1100
Daily utilization for lying in bed all the day 1650 Calory.
Daily utilization with doing heavy work about 6000 Calory
1-muscular exercise (most imp. Factor), maximal exercise can increase
The metabolic rate to 200 % of normal, there is increased O2 consumption
not only during exertion but also for some time after the end of the exercise to repay what is called O2 debt.
2-Recent food ingestion (specific dynamic action of food-SDA): it is defined as :it is the obligatory energy expenditure that occurs during food assimilation into the body .it is affected by :
a- type of food :an amount of proteins( provide 100 Kcal) can increase total metabolism by :
30 Kcal, a similar amount of carbohydrates increases it 6 Kcal& a similar
amount of fat increases it by 4 calories .
b- amount of food :because proteins has the highest SDA, the greater the proteins ingested, the more increase in metabolic rate. heat liberated after protein intake is taken from energy stores of the body, so prolonged protein intake can lead to loss of body weight& could treat obesity. Causes of SDA :↑sympathetic activity after food intake, extra energy is needed to glycogen from CHO, fatty acids stim. Metabolism.
SDA of proteins may be due to de-amination of amino acids in the liver or from the stimulatory effect of some amino acids on cellular chemical processes.
3-environmental temperature: when it is lower than body temp. the
metabolic rate increases due activation of heat conserving mechanisms
persons living in cold climate have increased thyroxin.
4-Fevers increase the metabolic rate because it increase the cellular chemical reactions. 1°c increases metabolic rate 14% of basal level.
5-Sympathetic stimulation increases metabolic rate due to liberation of catecholamines which causes muscle& liver glycogenolysis. also
Oxidative phosphorylation with heat liberation from cells of brown fat.
6-Sleep:metabolic rate falls to 15% below normal due to: decreased
Skeletal muscle tone& decreased symp. activity.
7-Age: it is greater in young child due to high rate of cellular reactions
needed for growth. 8- sex: metabolic rate is higher in males than
Females due to stimulatory effect of testosterone& great muscle bulk.
9-Hormones : sex hormones, thyroxine& growth hormones, all
stimulate cellular metabolism.
10-malnutrition decreases metabolic rate due to decrease in circulating catecholamines& thyroid hormone specially with prolonged starvation with decresed necessary food substances in the cells . ↓ of about 30 %.
11- Emotional state: anxiety& tension elevate the metabolic rate
due to increased epinephrine, but depression decreases metabolic rate.
12-Race: pure races as Chinese and Indians have a lower BMR than mixed races as Americans & Egyptians.
Hunger: it means craving (strong desire) for
food+ hunger contraction of stomach.
Appetite :means desire for a specific type
Satiety: means feeling of fulfillment in the
Quest for food.
1- hypothalamic center:
a- feeding (hunger c.):in lateral hypothalam.
b- satiety center:in ventromedial nucleus of
2- other centers : a-the amygdala& prefrontal
cortex(they belong to limbic system).
b-brain stem centers as
salivation& swallowing, they r excited by
signals from hypothalamus.
a-Nutritional regulation: glucostatic, lipostatic &
aminostatic theories.neurons r affected by :level
of blood glucose, fatty acids &amino acids and
then stimulation of either feeding or satiety
b-effect of body temperature: cold exposure
c-feed-back signals from adipose tissue: it releases leptin to inform the hypothalamus about energy storage.
-A- alimentary factors:
B- psychological factors:
Sight, smell& taste of food, all affect food intake……..(further readings)
In order to compare the metabolic rates of different persons, which result
from the inherent activity of the tissues without the effect of exercise and
external factors , the metabolic rate is measured the so called basal conditions. It is called basal metabolic rate. (BMR)
Definition : it is the rate of energy output measured under the following
1- complete physical and mental rest .
2- in the post absorptive state or after 12-14 hours after last meal.
3- at a comfortable room temperature which from 20-25°c for dressed person ( no shivering , no sweating )
BMR is expressed in K Cal / m² / h. It is usually expressed as a percentage of increase or decrease above or below the normal standard value for age and sex. normally it is± 15% of normal value
Factors affecting BMR are those affecting the metabolic rate except the effect of exercise, food intake& environmental temperature
Diseases that increase BMR :
1- hyperthyroidism (100% ↑ ) 2-hype- pituitrism.
5- blood diseases as polycythemia & leukemia with over activity of bone marrow.
6- heart failure with increased respiratory muscle activity.
7- diabetes insipidus with heat loss in urine.
Exogenous factors as:caffeine ,
Adrenaline, amphetamine& thyroxine.
Diseases that decrease BMR :
3-hypo function of adrenal crtex.
4-under nutrition& starvation.
6-hypothermia as during surgical operations.
Exogenous factors as: propyl-