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Nutrition is the science of nourishing the body.
Nutrition may be defined as utilization of food
by living organisms.
Food is the fuel source of the body.
The ingested food undergoes metabolism to
liberate energy required for growth,
maintenance of tissues of body & regulation of
body process.
Based on chemical nature, nutrients are
classified into six classes:
Carbohydrates
Lipids
Proteins
Minerals
Vitamins
Water
Based on biological role:
Nutrients are classified into energy providing
nutrients & protective nutrients
Energy providing nutrients:
Carbohydrates & lipids
Protective nutrients:
Proteins, minerals, vitamins & water.
Based on daily requirement:
Classified into macronutrients & micronutrients
Calorie:
A physiological calorie (kilocalorie) is defined
as the amount of heat required to raise the
temperature of one kilogram of water by one
degree centigrade.
Determination of caloric value of foods:
By using the bomb-calorimeter.
Bomb-calorimeter is a metal vessel in which the
weighed food is ignited in an atmosphere of
oxygen under pressure by electric spark.
A measured volume of water surrounds the
vessel.
When the temperature is multiplied by the
volume of water surrounding the vessel, the
total number of calories liberated by the
combustion of the food is obtained.
Bomb-Calorimeter
Gross caloric values:
By using bomb-calorimeter
1gm of carbohydrates yields 4.1 calories
1gm of fat yields 9.4 calories
1gm of proteins yields 5.4 calories
Digestible caloric values:
Digestible caloric value of foods are
1gm of carbohydrates = 4.0 calories,
1gm of fat = 9.0 calories
1gm of proteins = 5.2 calories.
Note:
Proteins are not completely oxidized in the
body.
The end product is urea, it contains some
amount of potential energy (1.25 calories/gm)
The oxidizable caloricfic value of protein =4.0
Actual caloric values:
1gm of carbohydrates = 4 calories,
1gm of fat = 9 calories
1gm of proteins = 4 calories.
Ethanol = 7 calories.
The respiratory quotient (RQ) is the ratio of
the volume of CO2 produced to the volume of
O2 utilized in the oxidation of foodstuffs.
Volume of CO2 produced
Volume of O2 usedRQ =
Done by open circuit method
The subjects breaths in the atmospheric air of
known composition.
The expired air is collected in a rubber bag or
spirometer.
The volume of expired air, the O2 content &
CO2 content are measured.
RQ is calculated by using the formula.
Carbohydrates:
The carbohydrates are completely oxidized.
R.Q .for carbohydrate = 1
Fats:
Fats have relatively lower R.Q.
They have a low oxygen content.
Fats require more O2 for oxidation.
R.Q. for the oxidation of the fat = 0.7
Proteins:
The chemical nature of proteins is highly
variable
The R.Q. of protein is 0.8
Mixed diet:
R. Q. of the diet consumed is dependent of
the relative composition of carbohydrates,
fats and proteins.
For a normal diet, it is around 0.8.
Three process to meet fuel demand of the
body…….
Basal metabolic rate (BMR)
Specific dynamic action (SDA)
Physical activity.
BMR is defined as the minimum amount of
energy required by the body to maintain life
at complete physical and mental rest in the
post-absorptive state (i.e. 12 hours after the
last meal).
It may be noted that resting metabolic rate
(RMR) is in recent use for BMR.
Several functions within the body
continuously occur.
These include working of heart & other
organs, Respiration, Blood circulation,
Conduction of nerve impulse, Reabsorption
by renal tubules, Gastrointestinal motility &
ion transport across membranes, Na+ -K+
pump, Synthesis of macromolecules.
Prerequisite conditions:
Post-absorptive state
Mental & physical relaxation
Person is awake
Temperature maintained at 20-25°C
Supine position.
Measurement:
The BMR is determined either by the apparatus
of Benedict & Roth (closed circuit device) or by
the Douglas bag method (open circuit device).
By Benedict-Roth method, the volume of O2
consumed (recorded on a graph paper) by the
subject for a period of 2-6 minutes under basal
conditions is determined.
The energy consumed is calculated from
oxygen consumption.
The oxygen consumed per hour is multiplied
by constant 4.825 calories.
One liter of oxygen consumption is equivalent
to 4.825 calories, when RQ of diet is 0.82.
For the calculation of body surface area, the simple formula by Du Bois and Du Bois is used.
Body surface area =
A = H0.725 x W0.425 x 71.84
A = Surface area in cm2
H = Height in cm
W = Weight in kg.
H0.725
x W0.425
x 71.84
Benedict & Roth Instrument
BMR is expressed as cal/sq.m/hr
Adult males: 38 cal/sqm/hr
Adult females: 33 cal/sqm/hr
The average body surface area for Indian
males is 1.62 sqm
For females = 1.4 sqm
Surface area:
BMR is directly proportional to surface area.
Surface area is related to weight & height.
Sex:
Men have higher (about 5%) BMR than women.
Due to the higher proportion of lean muscle mass
in men.
Age:
In infants & growing children, with lean muscle
mass, the BMR is higher.
In adults, BMR decreases at the rate of about
2o% per decade of life.
Physical activity:
BMR is increased in persons (athletes) with
regular exercise.
Due to increase in body surface area.
Hormones:
Thyroid hormones (T3 & T4) have a stimulatory
effect on the metabolism of the body & BMR.
Epinephrine, cortisol, growth hormone & sex
hormones increase BMR.
Environment:
In cold climates, the BMR is higher compared to
warm climates.
Starvation:
During the periods of starvation, the energy
intake has an inverse relation with BMR, a
decrease up to 50%
Fever:
Fever causes an increase in BMR.
An elevation by more than 10% in BMR is
observed for every 1°C rise in body
temperature.
Disease states:
BMR is elevated in various infections,
leukemias, polycythemia, cardiac failure, HTN.
In Addison's disease BMR is lowered.
BMR is important to calculate the calorie
requirement of an individual & planning of diets.
Determination of BMR is useful for the
assessment of thyroid disorders.
BMR is increased in thyrotoxicosis
(hyperthyroidism).
BMR is decreased in hypothyroidism.
The phenomenon of the extra heat production
by the body, over and above the calculated
caloric value, when a given food is
metabolized by the body, is known as specific
dynamic action (SDA).
It is also known as calorigenic action or
thermogenic action or thermic action (effect)
of food.
SDA for different foods:
For a food containing 25 g of protein, the heat
production from the caloric value is 100 Cal (25
x 4 Cal).
When 25 g protein is utilized by the body, 130
Cal of heat is liberated.
The extra 30 Cal is the SDA of protein.
SDA for protein, fat and carbohydrate 32%, 13% & 5%,
Proteins possess the highest SDA while carbohydrates
have the lowest.
SDA for mixed diet:
The presence of fats & carbohydrates reduces the SDA
of proteins.
Fats are most efficient in reducing SDA of foodstuffs.
For a regularly consumed mixed diet, the SDA is
around 10%
For the utilization of foods by the body, certain
amount of energy is consumed from the body
stores.
Expenditure by the body for the utilization of
foodstuffs.
It is the highest for proteins (30%) & lowest for
carbohydrates (5%) & for mixed diet 10%
Additional 10% calories should be added to the
total energy needs (of the body) towards
SDA.
The higher SDA for protein indicates that it is
not a good source of energy
SDA of foods is due to the energy required for
digestion, absorption, transport, metabolism
and storage of foods in the body.
The SDA of proteins is primarily to meet the
energy requirements for deamination,
synthesis of urea, biosynthesis of proteins,
synthesis of triacylglycerol (from carbon
skeleton of amino acids).
Phenylalanine, glycine and alanine increase
the SDA.
The SDA of carbohydrates is attributed to the
energy expenditure for the conversion of
glucose to glycogen.
Fat, the SDA may be due to its storage,
mobilization and oxidation.
Consumption of protein rich diet cold climates:
In cold climates, diet rich in proteins is
recommended, it helps to maintain the body
temperature.
Due to its high SDA, liberates extra heat.
The energy requirement depend on the
occupation, physical activity and lifestyle of
the individual.
Light worker (teachers, doctors) 30-40%BMR
Moderate worker (housewives, students)40-50% BMR
Heavy work (labourers) 50-60% BMR
Very heavy work (workers & rickshaw pullers)
60-100% BMR
Individual with light work about 60% of the calories
are spent towards BMR, about 30% for physical
activity & about 10% to take care of the SDA.
Light work 2,200 – 2,500 Cal/day
Moderate work 2,500 – 2,900 Cal/day
Heavy work 2,900 – 3,500 Cal/day
Very heavy work 3,500 – 4,000 Cal/day
Low temperature increases energy expenditure by
inducing shivering & nonshivering thermogenesis
Shivering provides heat by increasing muscle activity
in response to cold stress.
Nonshivering thermogenesis also produce heat.
It is due to brown adipose tissue.
It is stimulated by epinephrine & norepinephrine.
1. Define BMR. How it is determined? Describe the factors affecting the BMR. Mention the significance of BMR.
2. Define SDA. Mention the SDA for proteins, fats and carbohydrates. Mention its significance.
3. Define RQ. Mention the significance of RQ.
Medical Biochemistry - AR Aroor
Text book of Biochemistry - U.Satyanarayana
Biochemistry – Pankaja Naik
Text book of Biochemistry – DM Vasudevan
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