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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 l.jpg

Energy balance &metabolic rate

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Metabolism means changes , it is used to refer to all chemical andenergy transformation processes that occur in the body.

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.

High energy compounds l.jpg
High energy compounds : chemical and

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 .

Units of heat energy l.jpg
Units of heat energy: chemical and

  • 1-The calorie :(cal, gram calorie, small calorie, or standard calorie): it is the amount of heat energy necessary to raise the

  • temperature of one gram of water 1 degree from 15°c to 16°c.

  • 2- The kilo- calorie (Kcal, the Calorie): it equals 1000 cal, and is the unit which is commonly used in physiology& medicine.

  • Energy balance :

  • In the body there is an energy balance between caloric intake ,

  • provided by the absorbed food, and energy output. If the caloric intake is less than the energy output, the balance is negative and there is weigh loss by catabolism of glycogen fats & proteins.

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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.

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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

Metabolic rate energy output l.jpg
Metabolic rate ( energy output ) physical

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.

Direct calorimetry l.jpg
Direct calorimetry : physical

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.

Indirect calorimetry l.jpg
Indirect calorimetry physical

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.

The respiratory qutient rq l.jpg
The respiratory qutient(RQ) physical

  • It is the ratio (in the steady state) of the volume of CO2 produced to the

  • Volume of oxygen consumed per unit of time

    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 CHO= 6/6 = 1

    RQ for fat = 102/ 145 = 0.7

    RQ for protein = 0.82

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Contin. Imp. Of physicalRQ

  • 2- Determination of precise energy equivalent of O2:

    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

Continu imp rq l.jpg
Continu. Imp. physicalRQ

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

Factors increasing rq l.jpg
Factors increasing RQ : physical

  • Hyperventilation , severe muscular exercise , metabolic acidosis and fevers .

  • Factors decreasing RQ :

  • Hypoventilation & apnea . Metabolic alkalosis (due to retention of CO2) , recovery from exercise : due to use of CO2 in reformation of bicarbonate which was used up in the beginning of exercise. RQ may reach 0.5 .

  • - in diabetes Mellitus ( untreated ) RQ is 0.7

  • - during HCL secretion , Stomach has negative RQ it takes more CO2 from arterial blood than out put to venous blood.

  • - RQ of brain & cornea equal 1(main fuel is glucose )

Metabolic table l.jpg
Metabolic table: physical

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

Energy requirements l.jpg
Energy Requirements physical

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

Lactation+ 500

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Calculation of B.M.R physical

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 %


Energy expenditure per hour during different types of activity for a man 70 kg l.jpg
Energy expenditure per hour during different types of activity for a man 70 Kg

Type of activity Calories per hour.

Sleeping 65

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

Swimming 500

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

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Factors affecting the metabolic rate activity for a man 70 Kg:

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.

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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.

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Cntin. Factors affecting metabolic rate the liver or from the stimulatory effect of some amino acids on cellular chemical processes.

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.

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Regulation of food intake the liver or from the stimulatory effect of some amino acids on cellular chemical processes.

Hunger: it means craving (strong desire) for

food+ hunger contraction of stomach.

Appetite :means desire for a specific type

of food.

Satiety: means feeling of fulfillment in the

Quest for food.

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Neural centers for regulation the liver or from the stimulatory effect of some amino acids on cellular chemical processes.of food intake

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.

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Factors regulating food intake the liver or from the stimulatory effect of some amino acids on cellular chemical processes.

1-long-term regulation:

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

causes over-eating.

c-feed-back signals from adipose tissue: it releases leptin to inform the hypothalamus about energy storage.

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2- short-term regulation: the liver or from the stimulatory effect of some amino acids on cellular chemical processes.

-A- alimentary factors:

i-gastro-intestinal filling.

ii-gasro-intestinal hormones.

iii-oral factors.

B- psychological factors:

Sight, smell& taste of food, all affect food intake……..(further readings)

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The basal metabolic rate the liver or from the stimulatory effect of some amino acids on cellular chemical processes.

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

basal condition:

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 changes bmr l.jpg

Diseases that increase BMR : the liver or from the stimulatory effect of some amino acids on cellular chemical processes.

1- hyperthyroidism (100% ↑ ) 2-hype- pituitrism.

3- hyper-adrinalism.

4- fevers.

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.

5-shock& nephrosis.

6-hypothermia as during surgical operations.

Exogenous factors as: propyl-

thiouracil, iodides.

Diseases that changes BMR