Proteins


 Introduction

Dietary protein carries out three nutritional roles. Protein is essential for the development, upkeep, and repair of bodily tissue. It also controls important bodily functions and can be used as an energy source in excess. The twenty amino acid molecules required for protein synthesis are the building blocks of all proteins. proteins provide 4 kilocalories of energy per gram.

Functions of proteins

  • growth and maintenance of tissue
  • formation of essential body compounds
  • transport of nutrients across the cell
  • regulation of water balance
  • maintenance of appropriate pH
  • defense and detoxification
  • source of energy
  • helps in chemical processes like digestion
  • enzymatic and hormone function
  • synthesise and repair DNA
  • provise structural support (for skin, hair, etc.)
  • immunity

Nutritional classification of Proteins

  1. Complete proteins - egg, albumin, milk caesin (10 essential amino acids)
  2. Partially complete proteins - wheat and rice (partially lacks 1-2 amino acids)
  3. Incomplete proteins - gelatin, zein (completely lacks 1-2 amino acids)

Nutritional classification of Amino Acids

  1. Essential amino acids: cannot be synthesised by the body
  2. Non-essential amino acids: can be synthesised by our body
  3. Conditionally essential amino acids: needed for the diet

Protein digestion

  • Mouth- Chewing breaks food apart and leave more surface area for digestion
  • Stomach- Hydrochloric acid and pepsin breaks central bonds in proteins, protein is divided into peptides
  • Small intestine- Peptides are further broken down into amino acids through hydrolysis and then amino acids are absorbed by small intestine and carried to bloodstream.

Metabolism

The majority of amino acids are primarily absorbed in the liver. The primary metabolic pathways in charge of preserving the body's homeostasis of proteins and amino acids are:

  • protein synthesis
  • protein breakdown/degradation
  • amino acid inter conversions
  • amino acid synthesis

Compared to fats and carbs, proteins require more water for metabolism. If protein intake is increased, water intake should also be increased to prevent dehydration.

Factors affecting protein utilisation

  • Amino acid balance
  • calorie intake
  • immobility
  • injury
  • Emotional stability

Complementary value of protein

Nitrogen balance cannot be maintained in a diet that is severely lacking in one or more necessary amino acids in its protein content, regardless of how well-rounded and comprehensive the diet may be in other areas. Proteins have a property known as their complementary or supplemental value, which allows them to compensate for each other's shortcomings.

Ex: legumes + cereals, cereals + milk & milk products, legumes + nuts & oil seeds

Sources

Animal protein sources: These include milk, egg, meat, fish, poultry and milk products like cheese, curd, khoa. These foodstuffs have good quality proteins or complete proteins as they are completely used up by the body.

Vegetable protein sources: Pulses  whole and split, soyabeans, nuts and oil seeds like peanuts, almonds and cashew nuts are rich sources of vegetable protein. Cereals like wheat and rice also provide some amount of protein. It is nutritionally better to use a mixture of cereals and pulses at a meal rather then using either cereals or pulses alone.

Since, Proteins are the chief component of all body tissues, and are the "workhorses" of the body, we should add adequate amount of proteins into our diet in order to keep our muscles & tissues healthy as well as provide ourselves with energy for bodily functions.


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