Nutrition

Gandham.RajeevEmail:gandhamrajeev33@gmail.com

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.

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