Dr.Humeda Suekit Humeda

0912628881

In physiological processes energy is measured

in Kcal = Kilo calorie = Calorie

A calorie (gram c - , small c - , standard

calorie):

Is the amount of heat energy that can rise

the temperature of 1 gram (1 ml) of water 1°from 15° to 16°C

Kcal = 1000 calorie

The amount of energy expenditure or usage in

the body is called the

The metabolic rate:

Amount of energy used/consumed in the

body in a unite of time

Energy consumption (metabolic rate) can be divided

into distinct components:

1- Basal metabolism

2-Diet induced thermogenesis;

Specific dynamic action of food (SDA):

Obligatory energy expenditure following ingestion

of food ( for digestion, absorption and metabolism)

SDA of proteins is 5-6 times that of fat and CHO

3- Nonshivering thermogenesis:

Energy expended for the purpose of

producing

heat to maintain normal body

temperature

4- Physical activity : variable degree of energy

output

According to the low of thermodynamics

energy can not be created or lost but it can

be transformed from one form of energy to

another

Metabolism is the sum of all chemical processes or

transformations in the body

A. Catabolism:

Any reaction that involves the slow and stepwise

breakdown of compounds to simpler molecules

-catabolism liberate energy

B. Anabolism:

The synthesis of complex compounds from simpler

molecules

Anabolic reactions consume energy

in Anabolic reactions energy can be stored in the

form of proteins, carbohydrates , fats and energy rich

phosphate compounds (ATP, Creatine )

Energy nutrients are used to synthesis ATP

(Adenosine Tri Phosphate ) by oxidative

reactions

ATP Directly transfer energy from food to all

functional cellular systems

When food is burned outside the body the

amount of energy produced can be measured

using

Bomb calorimeter

The caloric value of food is the amount of

energy liberated when one gram of the food

stuff is oxidized

The caloric value of food when it is burned

outside the body is =

Carbohydrates = 4.1 Kcal/ g

Proteins = 5.3 Kcal/g

Fat = 9.3 kcal/g

The same amount of energy (caloric value )

is obtained when food is oxidized inside the

body except for proteins because the

oxidation of proteins is incomplete (urea and

other nitrogenous products)

The caloric value of food when it is catabolized inside

the body is =

Carbohydrates = 4.1 Kcal/ g

Proteins = 4.1 Kcal/g

Fat = 9.3 kcal/g

Metabolic rate=

- Rate of energy expenditure or usage in the

body

- Amount of energy used in a unite of time

- Metabolic rate was less than energy input =

weight gain

- Metabolic rate was more than energy input

=weight loss

Energy consumption (metabolic rate) can be divided

into distinct components:

1- Basal metabolism

2-Diet induced thermogenesis;

Specific dynamic action of food (SDA)

3- Nonshivering thermogenesis:

4- Physical activity : variable degree of energy output

Affected by many factors :

1. Age (growth, active tissue)

2. Sex

3. Height, weight and surface area

(linear relationship = 3.5W )

4. Physiological factors

( Pregnancy, lactation, ovulation)

5. Exercise

0.75

6. Ingestion of food (SDA)

7. Body temperature

8. Environmental temperature

9. Sleep

10. Prolonged fasting

11. Emotional state

12. Hormones (thyroid hormones and catecholamines)

It is the rate of energy expenditure in basal or resting

conditions

Provide a mean to compare between individuals

Basal conditions=

1- Physical and mental rest

2- Fasting for at least 12 hours (post- absorbative state

3-Comfortable temperature (20- 27°C)

Represent the state of minimal energy expenditure

At rest energy is used in basal functions:

1- Synthetic and degradative chemical reactions

2-Membrane transport to maintain ion gradients

3- Signal generation and conduction in the nervous system

4- Mechanical work of respiration and circulatory system

5- Muscle tone

Factors affecting BMR:

1. Lean body mass and body surface area

BMR is linearly related to the two factors

2. Age: decreases in elderly

3. Gender: females have less BMR compared to males

4. Genetic factors

5. Physiological factors: pregnancy and lactation increase BMR

6. Pathological factors: febrile illness increase BMR

7. Hormones : Catecholamines and Thyroid hormone increase BMR

BMR in an adult=

70 Kcal/hour

1500 -2000 kcal/day

40 Kcal/m2/h

In humans, the energy required for life

processes is produced by oxidizing energy

nutrients;

1. Carbohydrates

2. Proteins

3. Fat

oxidation give H2O, CO2, heat and energy

CalorimetryDirect = measures the heat produced by the

body

research purpose only ( chamber

)

CalorimetryA. Direct calorimetry

= measures the heat produced by the body

( research purpose only ( chamber )

B. Indirect calorimetry

O2 consumed

CO2 produced

H2O produced

Oxygen consumption can be measured by:Spirometer

measure the O2 consumption

1- Direct = Benedict Roth

spirometer

2- indirect = Analyzing expired air

O2 consumed can be used to calculate

energy expenditure:

We should know :

The type of food consumed

The caloric equivalent of each type of food

When food is oxidized it provides a

characteristic amount of energy (caloric

value of nutrients)

It also consumes a fixed amount of O2

and produces a fixed amount of CO2

depending on the ratios of O2+, Carbon and

H+ in the molecular structure of the nutrient

Calorie

value

Kcal/ gram

O2 used (L/g) Calorie

equivalent of

O2

Kcal/L of O2

Respiratory

quotient

Carbohydrate 4.1 0.84 5 1Fat 9.3 2 4.7 o.7Proteins 4.1 0.96 4.5 0.8Typical fuel mix 4.8 0.85

RQ=

Is the ratio of CO2 produced for O2 consumed in the

steady state

Varies depending on the nutrient

Carbohydrates RQ =1

Fats RQ =0.7

Proteins = Average 0.8

Mixed diet = 0.8 -0.85

Proteins:

- Variable

- Due to different side chains and different amino acids

combinations

- An average value was estimated to be around 0.8

RQ can be used to determine the type of

nutrient used as an energy source by an

individual or even an organ

RQ is used to calculate the energy output of

the individual (metabolic rate)

Calorie equivalent of O2:

The amount of energy in Kcal obtained by

consuming one liter of O2

Ex: if one liter of O2 was used to oxidize

CHO the amount of energy liberated = 5 Kcal

CHO = 5 Kcal/L of O2

Fat= 4.7 Kcal/L of O2

Proteins = 4.5 Kcal/L of O2

Calorie or joule equivalent of O2 are used to

measure the energy liberated by an

individual through measuring the amount of

O2 consumed and CO2 produced (RQ).

Quantity of energy liberated per liter of O2

consumed in the body average = 4.8 Kcal/L

Calorie

value

Kcal/ gram

O2

used

(L/g)

Calorie equivalent of O2

Kcal/L of O2

Respiratory

quotient

Carbohydrate 4.1 0.84 5 1Fat 9.3 2 4.7 o.7Proteins 4.1 0.96 4.5 0.8Typical fuel mix 4.8 0.85

Positive energy balance:

energy gain is more than energy expenditure

excess energy is converted to storage

results in weight gain

Negative energy balance:

Energy gain is less than energy expenditure

Energy stores are consumed

Results in weight loss ( decrease in glycogen,

fats and proteins)