PROTEIN

A protein is a complex, high- molecular- weight organic compound that consists of amino acids joined by peptic bonds. Proteins are essential to the structure and function of all living cells.  Many proteins are enzymes or subunit of enzymes.

Proteins are primary structural and functional components of every living cell. Almost half the protein in our body is in the form of muscles and the rest of it is in bone, cartilage and skin. Proteins are composed of different amino acids. Certain amino acids are termed as Essential Amino Acids because they are not synthesized by the body but are taken from the outside in the form of the diet. Non essential amino acids can be synthesized by the body.

Protein requirements vary with age, physiological status and stress. More proteins are needed by growing infants, children, body builders, pregnant women and individuals having some infection, illness or stress. Rich sources of proteins are from animal foods like milk,  meat, fish, eggs  and plant foods like pulses and legumes. Animal proteins are of high quality because they provide all essential amino acids. Plants and vegetables are not of the same quality because of their low content of some essential acids.

WHAT DO PROTEINS DO ?  

FUNCTIONS

Proteins are involved in almost all functions of a cell including cellular functions like Signal Transduction and Metabolism.

WITHIN NUTRITION

Protein is taken in large quantity in diet and is called macronutrient. Requirement of proteins depends upon age, sex, level of physical activity, medical condition of the individual.  RDA is 0.8 to 1.2 gm/ kg body weight. Active athletes need 1 to 2 gm/kg body weight. Proteins are found in small quantity in all foods but rich sources of proteins are legumes, nuts and dairy products as choices for vegetarians.

TISSUE BUILDING

Protein is the major component in the regulation, growth and differentiation of muscles, tendons, enzymes, skin, hair, eyes and other organs and processes. The body can manufacture 11 amino acids out of 20 amino acids. The remaining 9 come from diet and are called Essential Amino acids. The food are converted to protein and ammonia through catabolism. Ammonia produces essential amino acids. Excess of ammonia may be converted to uric/acid/urine to be excreted. Animal proteins are called  Complete or high quality proteins. Plants lack two major amino acids which are found in animal proteins. They are lysine and methionine.

ENERGY SYSTEM

1 gm of protein on oxidation produces 4 k cals of energy.

METABOLIC FUNCTIONS

Protein helps in various functions through enzymes, hormones and antibodies.

TRANSPORT OF NUTRIENTS

Proteins as liquid form, are carrier of nutrients to cell membranes. Proteins as lipoproteins transport triglycerides, cholesterol and fat soluble vitamins.

FUNCTIONS OF AMINO ACIDS

(a) Tryptophan - Serve as a precursor of Vit B, niacin and serotonin.

(b) Glycine and Arginine- Synthesizes creatinine which form creatinine phosphate.

(c) Histidine - used in synthesis of histamine.

(d) Glutamic acid - neurotransmitter.

COMPLETE PROTEINS  VS  INCOMPLETE PROTEINS

Animal proteins are complete because they have all essential amino acids where as vegetable proteins do not have all essential amino acids. They lack Lysine & Methionine.

SOURCES OF COMPLEMENTARY PROTEINS

The deficiency of Lysine and Methionine can be made up by taking a combination of grains, legumes and nuts/ seeds.  Example Rice and beans can be taken together. Rice has Lysine and beans have Methionine. Same way many combinations can be made.

COMPLEMENTARY PROTEINS

Complementary proteins are two proteins in a food that compensate for one another's shortfalls when combined.

AMINO ACIDS

Amino acids are known as the building blocks proteins. They perform many important functions like building cells, protecting the body from viruses or bacteria, repairing damaged tissues and carrying oxygen throughout the body.

PROTEINS & WEIGHT MANAGEMENT

A high protein diet does not promote weight loss. When people reduce intake of carbohydrates while on weight reduction diet then role of proteins come into play. The body takes energy from the proteins in case carbohydrates level is too low.

Regards,

Col KG Sharma, Nutritionist