All About Proteins

• Proteins are the basic building block of every living cell and essential for growth, repair, and maintenance of health.
• Proteins contain carbon, hydrogen, oxygen, and nitrogen, distinguishing them from carbohydrates and fats.

Objectives

• The importance of proteins in our daily diet should be appreciated
• The difference between complete and incomplete proteins should be understood
• The chemical nature of proteins should be described
• The importance of including proteins of high biological value in meals should be understood.
• Rich sources of proteins should be listed
• Knowledge about novel sources of proteins available in the market should be acquired

Definition

Composition

• Proteins consists of chains of amino acids linked by peptide bonds.
• Amino acids contain a carboxyl group (COOH) and an amino group (NH2).

Classification

• Essential amino acids cannot be synthesized in sufficient amounts by the body and must be obtained through diet.
• Adults require eight essential amino acids, while growing children require ten.
• Non-essential amino acids are required for tissue synthesis and repair but can be synthesized by the body.

Digestion and Metabolism

Protein Quality

• The proteins that make up skin, bones, muscles, hair, and nails in the body vary.
• Egg, milk, meat, and pulse proteins differ in quality and quantity.
• Protein content in food is estimated by measuring nitrogen content, with 16% nitrogen in proteins..

Classification by Quality

• Complete proteins contain all essential amino acids in amounts to meet the body's needs.
• Partially complete proteins have one or more essential amino acids in inadequate amounts.
• Incomplete proteins cannot support growth or repair of body cells.

Functions in the Human Body

• Growth and synthesis of body cells, tissues, and fluids occur
• Maintenance and repair of the body happen
• Hemoglobin transports oxygen to tissue cells.
• Plasma proteins maintain water balance and regulate osmotic pressure.
• Antibodies protect by increasing resistance to disease.
• Enzymes and some hormones, like insulin, are made of protein.
• Insulin regulates blood sugar levels.
• Some amino acids, like tyrosine, form hormones like thyroxine.

Energy Source

Biological Value

• Like carbohydrates, proteins provide 4 kcal/g of energy when broken down.
• If the diet is deficient in calories, the body uses protein and fat stores for energy.
• Cereals and pulses consumed together have a higher biological value (BV) due to their complementary amino acids.

Methods of Improving Quality

• Including a small amount of complete protein food in each meal is important
• Combining plant foods can provide all essential amino acids.
• Mixtures of plant foods yield high-quality proteins.
• Consuming plant proteins with a small quantity of animal protein can be effective.

Synthetic Methods

• Synthetic amino acids are added to processed foods to compensate for deficiencies.
• Plant proteins are used to stretch the supply of expensive animal proteins and improve affordability.

Factors influencing protein requirements:

Dietary Sources Types

• Animal sources include high-quality proteins from eggs, milk, cheese, meat, fish, and poultry.
• Plant sources include pulses, soybeans, tofu, and nuts.
• Infant and growing children need more protein, 1.6-2 g/kg body weight.
• Protein requirements increase during illness as needed for rebuilding tissue.
• The diet should include adequate carbohydrates and fats for a protein-sparing effect.

Absorption And Processes

• After digestion, amino acids are absorbed in the small intestine, carried to the liver, and metabolized.
• End products of amino acid metabolism are carbon dioxide, water, and nitrogen.
• Nitrogen is excreted as urea by the kidneys.
• Excess amino acids cannot be stored by the body.
• Liver cells take in amino acids from the amino acid pool, converting them into glucose or keto acids.
• Excess protein intake can still be harmful.

Digestion and metabolism of protein

• Protein digestion begins in the mouth (mechanical digestion)
• Chemical digestion then starts, as it moves toward the stomach and intestines
• Protein is deaminated in the liver

Problems/Side Effects of Excess

Metabolism details

• Digestion:
  • Protein breaks down starting with mechanical digestion, then chemical digestion, then passes throught enzymes
• The body uses amino acids:
• To repair tissue
• For energy when neeed
• To oxidize tissue
• The body gets rid of excess protein:
  • By oxidization
  • By getting rid of the nitrogen

Types Of Protein Balances

• Nitrogen balance means that N intake (dietary protein ) = N output in urine (NH3, urea, uric acid ) . N balance is controlled by diet &hormones . Normally hormones control protein anabolism/ catabolism to maintain N balance.
• Positive N balance means more intake.
• Negative N balance means more output.
• Eating quality protein can balance those situations