introduction to nutrition and proteins

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INTRODUCTION TO NUTRITION AND PROTEINS

Santosh KIntern

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NUTRITION

• Nutrition may be defined as a science of food and its relationship with health.

• Nutrients are specific dietary constituents such as proteins, carbohydrates, fats, vitamins and minerals.

• Dietics is the practical application of principles of nutrition: includes planning of meals for the well and the sick.

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CHANGING CONCEPTS

• Nutrition is the corner stone of socio economic development.

• The concept that health sector alone is responsible for tackling the nutritional ills of the society has faded away.

• Broad inter- sectoral and integrated approach of sectors of development is needed to tackle today’s nutritional problems.

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• Specific nutritional deficiency diseases have been indentified and technologies developed to control them.

• Importance of nutrition for immunity, fertility, maternal and child health and family health have gained importance.

• Role of dietary factors in the pathogenesis of non communicable diseases like CHD, diabetes and cancer have gained importance.

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NUTRITIONAL EPIDEMIOLOGY :Epidemiological assessment of nutritional status of communities, nutritional and dietary surveys, nutritional surveillance, nutritional indicators and nutritional interventions-collectively called as nutritional epidemiology.

• Promotion of nutrition is one of the eight elements of primary health care.

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CLASSIFICATION OF FOODS

BY ORIGIN:a)Animal originb)Vegetable origin

BY CHEMICAL COMPOSITION:a)Proteinsb)Carbohydratesc)Minerals d)Fatse)Vitamins

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BY PREDOMINANT FUNCTIONS:a) Body building foods: eg. Milk ,meat, poultry, pulsesb) Energy giving foods: eg. Cereals, sugar, roots and tubers, oils and fatsc) Protective foods: eg. Vegetables, fruits, milk

BY NUTRITIVE VALUE:d) Cereals and milletse) Pulsesf) Vegetablesg) Nuts and oil seeds

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BY NUTRITIVE VALUE:e) Fruitsf) Animal foodsg) Fats and oilsh) Sugar and jaggeryi) Condiments and spices

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NUTRIENTS• Are organic and inorganic complexes contained in

food.

• They can be classified into 1.Macro nutrients2.Macro nutrients

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MACRONUTRIENTS: • They are also called as proximate principles. • In Indian dietary, they contribute to the total

energy intake in the following proportions: proteins: 7-15% fats: 10-30% carbohydrates 65-80%

MICRONUTRIENTS: Vitamins and minerals.

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PROTEINS

• The word protein by derivation means that it is of first importance.

• Proteins are complex organic nitrogenous compounds and composed of carbon, hydrogen , oxygen , nitrogen and sulphur in varying amounts.

• Proteins constitutes about 20 percent of the body weight in adults.

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• Polypeptides are made by polymerization of amino acids through peptide bonds

• Big polypeptide chains containing more than 50 amino acids are called proteins.

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PRIMARY STRUCTURE: determined by the sequence of amino acids

SECONDARY STRUCTURE: occurs when the amino acids are linked by hydrogen bonds.

TERTIARY STRUCTURE: formed when alpha helices and beta pleated sheets are held together by week interactions

QUARTERNARY STRUCTURE: consists of more than one polypeptide chains.

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• Out of the 20 amino acids needed by the human body, 8 are essential because the body cannot synthesize them in amounts corresponding to the needs and hence must be obtained from dietary sources.

• Essential amino acids are- leucine, isoleucine, lysine, methionine, phenylalanine, threonine, valine, tryptophan and Histidine.

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• A protein is said to be biologically complete if it contains all the amino acids in amounts corresponding to human needs.

• Animal proteins are superior to vegetable proteins as they are biologically complete.

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ASSESSMENT OF PROTEIN• PROTEIN QUALITY: is assessed by comparison to a

reference protein(egg protein).

• There are two methods of assessment of protein quality:

a)Amino acid score b)Net protein utilization

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• AMINO ACID SCORE:

Amino acid score=mg of amino acid per g of test protein ×100 mg of the same amino acid per gram

of reference protein Starches - 50-60 Animal foods – 70-80

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• NET PROTEIN UTILIZATION(NPU) : It is the product of digestibility coefficient and biological value divided by 100.

NPU= Nitrogen retained in the body × 100 Nitrogen intake

• In calculating protein quality, 1 g of protein is assumed to be equivalent to 6.25g of nitrogen.

• Total protein requirements varies with the NPU of dietary proteins.NPU of Indian diet varies between 50 and 80.

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• PROTEIN QUANTITY: one way of evaluating food as a source of protein is to determine what percent of their energy value is supplied by their protein .

protein energy ratio= energy from protein×100total energy in diet

It is recommended that protein should account for approximately 10-12 % of the total energy intake.

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SOURCES OF PROTEINS

• Animal sources: Milk , meat, eggs, cheese, fish

• Vegetable sources: Pulses, cereals, beans, nuts,

oils and seeds. • In India cereals and pulses are the main

sources of proteins as they are cheap, easily available and consumed in bulk.

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PROTEIN CONTENT OF FOODS

FOOD PROTEIN(g. per 100g.. Of food)

Milk 3.2 – 4.3Meat 18 – 26Egg 13Cereals 6 – 13 Pulses 21 – 28 Soyabean 43.2

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PROTEIN REQUIREMENTS

• ICMR expert group suggested an intake of 1gram of protein per kg of body weight for adult males and females , assuming NPU of 65 for dietary proteins.

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GROUP CATEGORY/AGE PROTEIN REQUIREMENT

MAN Sedentary workModerate workHeavy work

60g/d

WOMAN Non pregnant 55g/d

pregnant 78g/d

Lactating 0-6 m 74g/d

Lactating 6-12 m 68g/d

INFANTS 0-6 months 1.1g/kg/d

6-12 months 1.69g/kg/d

CHILDREN 1-3 years 16.7g/d

4-6 years 20.1g/d

7-9 years 29.6g/d

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GROUP CATEGORY/AGE PROTEIN REQUIREMENT

BOYS 10 – 12 Years 39.9 g/d

GIRLS 10 – 12 Years 40.4 g/d

BOYS 13 – 15 Years 54.3 g/d

GIRLS 13 – 15 Years 51.9 g/d

BOYS 16 – 17 Years 61.5 g/d

GIRLS 16 – 17 Years 55.5 g/d

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FUNCTIONS OF PROTEINS

A) Body building.B) Repair and maintenance of body tissues.C) Maintenance of osmotic pressure.D) Synthesis of substances like antibodies,

plasma proteins, hemoglobin, enzymes, hormones and coagulation factors.

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PROTEINS CLASSIFIED BY FUNCTION

• CATALYTIC : Enzymes.

• STORAGE: Ovalbumen (in eggs), casein (in milk), zein (in maize).

• TRANSPORT: Haemoglobin.

• REGULATORY:Hormones (eg. insulin) and neurotransmitters.

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• CONTRACTILE: Actin, myosin, dynein (in microtubules)

• PROTECTIVE: Immunoglobulin, fibrinogen, blood clotting factors

• STRUCTURAL: Cell membrane proteins, keratin (hair), collagen .

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PROTEIN METABOLISM• Proteins are not stored in the human body.• They are constantly broken down into their

constituent amino acids and then reused for protein synthesis.

• The overall turnover in adult man is equivalent to replacement of 1-2% of the body protein each day.

• The amount of a specific protein in the body is kept constant.

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DEFICIENCY DISEASES

• Protein deficiency occurs along with energy deficiency, hence called PROTEIN ENERGY MALNUTRITION.

• The current concept of PEM has two clinical forms- KWASHIORKOR and MARASMAS.

• They can be prevented by health promotion, good diet, immunisation, food fortification, early diagnosis and treatment and rehabilitation.

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REFERENCES

• Park K . Textbook of Preventive and Social Medicine. 22nd ed. Banarasidas Bhanot publishers;2013: 563-565,588-589,592

• Vasudevan DM . Text book of biochemistry. 5th ed. Jaypee brothers medical publishers;2009:18,21,27,31- 32

• ICMR:recommended dietary allowances available from url( www.icmr.nic.in/final/RDA-2010.pdf ) accessed on 22/8/14 at 8:00PM.

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