Introduction
Nutrition comes from the six components of the food that are carbohydrates, proteins, and fats as major components and vitamins, minerals, fiber, and water. All these elements perform various physiological functions in the human body like body preservation, body composition, production of heat and energy in the body, digestive tract contractions, control of heartbeat, lung and muscle contractions, etc. Below is a discussion of the role of protein in nutrition (3) & (5).
What is protein?
Protein is the main component of human body cells first discovered in 1938, by the scientist Mulder. The word protein comes from the Greek word, “proteo”, which means to occupy the first place. The organic compounds that combine carbon, hydrogen, oxygen, and nitrogen to play a key role in the formation and depletion of the organism are called proteins (1).
Properties
1. All proteins contain carbon, hydrogen, oxygen, and nitrogen thus it is a macronutrient.
2. Nitrogen content is 16% in a protein and some contain sulfur.
3. Multiple amino acids are found in protein analysis.
4. Proteins do not allow conflicts between different chemical processes in the body.
5. Due to the presence of nitrogen in protein, helps the body to grow and make up for the lack of fats and carbohydrates.
6. The nutritional value of protein depends on the presence and quantity of essential amino acids and the easy digestibility of the protein (6) & (2).
Why is a protein called body-building food?
Protein is taken as the body-organizing and body-preserving food thus is the main component. Proteins are the building blocks of human body cells, muscles, blood, and other life-sustaining substances. So protein is called body-building food (2).
Building blocks of protein
1. Like carbohydrates, proteins also contain carbon, hydrogen, oxygen, and nitrogen.
2. The amino acid is the main component of protein. It is obtained by breaking down proteins into smaller parts. That is why amino acids are called building blocks of proteins.
3. Each amino acid contains at least one amino radical (NH₂) and one carboxyl radical (COOH). The carboxyl group is acidic and the amino group is alkaline.
The amino radical of one amino acid is combined with the carboxyl radical of the other amino acid.
Thus a linkage is formed between two amino acids (NH- CO). This linkage (NH- CO) is called a peptide bond.
In this way, by joining the peptide bond and releasing one molecule of water, di, tri tetra, and finally many acidic polypeptides are formed.
A protein molecule can be made up of one or more polypeptides. Many amino acids are then added to form a large protein molecule (1).
Sources of Protein
The presence of a proper amount of protein in the food increases the nutritional value thus helping in bodybuilding. There are both vegetable and animal sources of protein. Fish, meat, eggs, milk, cheese, dried pulses, nuts, soybeans, etc. are rich in protein. Ingredients that contain moderate amounts of protein are grain, millet, and young beans. Potatoes and some green leafy vegetables contain very little amount of protein. Meat, fish, eggs, and milk are animal proteins, and grain, millet, beans, pulses, and soybeans are vegetable proteins (5) & (7).
The amount of protein is some of the sources of protein is discussed with the help of a table.
| Sources | Amount of protein per 100 gm |
| 1. Meat | 26 |
| 2. Chicken breast | 31 |
| 3. Fish | 22 |
| 4. Boiled egg | 13 |
| 5. Soybeans | 36 |
| 6. Cheese | 25 |
| 7. Mung beans | 24 |
| 8. Lentils | 25 |
| 9. Milk | 3.4 |
| 10. Nuts (almonds, hazelnuts, walnuts) | 14- 21 |
| 11. Brown Wheat flour | 11 |
| 12. White bread | 9 |
| 13. Lean pork chop | 22.5 |
| 14. Pumpkin seeds | 18 |
| 15. Green peas | 5 |
| 16. Nutritional yeast | 50 |
Classification
Proteins are divided into three types.
1. According to the nutritional value
The nutritional value of protein depends on the presence and amount of amino acids. On this basis proteins are of three classes.
A. First-class protein
The essential amino acids in fish, meat, eggs, milk, etc. are in a balanced state. They are useful for bodybuilding. Foods from the animal kingdom are usually first-class proteins.
B. Second class protein
Pulses, nuts, flour, etc. are second-class proteins. Proteins usually obtained from plants are second class. These foods do not contain amino acids in a balanced state.
C. Third class protein
Nutrition or growth is not achieved by this type of protein. They do not contain amino acids. Sometimes these proteins produce heat in the body. So these are unsuitable or incomplete proteins. Such as gelatin.
2. According to the origin
According to the origin, there are two types of proteins.
A. Animal protein
These proteins are called animal proteins because they originate from the animal kingdom. These are fish, meat, eggs, milk, cheese, etc.
B. Vegetable protein
This type of protein is found in plants. These types of proteins are pulses, nuts, soybeans, etc. (3)
3. According to the structure
According to the chemical structure, there are three types of proteins.
A. Simple protein
Proteins that are made up of only amino acids are called simple proteins. Albumins, globulins, protamine, gliadin, albuminoids, histones, etc. are simple proteins.
B. Conjugated protein
Simple proteins that form a compound when combined with a non-protein or chemical substance are called conjugated proteins. These types of proteins are lipoproteins, glycoproteins, nucleoproteins, phosphoproteins, hemoproteins, flavoproteins, metalloproteins, phytochromes, cytochromes, opsins, and chromoproteins.
C. Derived protein
Proteins that are produced as a result of physical and chemical reactions during the digestion of proteins or when the combined proteins are hydrolyzed are called derived proteins. Examples of derived proteins are proteoses, metaproteins, peptones, polypeptides, proteins, peptides, etc. (1) & (2)
Role of protein in human nutrition
Proteins play a number of major roles in the nutrition of the human body.
1. Body growth and protection
Proteins are organic compounds that are made up of nitrogen. It plays an important role in the growth and depletion of the body. Protein actively helps human growth and depletion from birth to a certain age. Lack of protein impairs growth and depletion.
2. Growth of the fetus
When a human embryo is in the womb, it needs protein to grow. Lack of protein in the body of a pregnant woman impairs the growth of the fetus.
3. Breast milk production
Casein, lacto-albumin, and lactoglobulin, which are essential for breast milk production, are synthesized from proteins. In the absence of protein, those components cannot be synthesized in breast milk. As a result, it is not possible to meet the protein needs of the baby’s body.
4. Enzyme synthesis
Proteins play an important role in the formation of various enzymes in the human body.
5. Disease Prevention
The amino acids in food build up the body’s immune system by producing antibodies. It protects the human body from infection.
6. Hormone production
Proteins participate in the production of different types of hormones in the human body for cell metabolism. Some of these hormones are insulin, glucagon, ACTH, GTH, STH, TSH, MSH, oxytocin, vasopressin, etc.
7. Acid and alkali equilibrium
Protein acts as a buffer for the human body to maintain the balance of acids and alkalis.
8. Carbohydrates and fats synthesis
Protein causes the synthesis of carbohydrates and fats in the body through the process of deamination and transamination of nitrogen-free amino acids (1) & (6).
The daily amount of protein in the diet
Protein needs depend on body size, age, digestion, and absorption capacity. According to nutritionists, 1 gm of protein is needed daily for every kilogram of body weight of an adult. Children need 1.5- 2.0 gm of protein per kilogram of body weight. Pregnant women need 15 gm more protein than usual. Maternity women require 25gm more protein for the first six months and then 18 gm more protein up to 6- 12 months.
But if a man or woman is overweight, then the amount of protein should be reduced and if underweight, the amount of protein should be increased. Humans need to have 25- 30 % of the protein in their daily diet chart (6).
| Groups | Recommendation of protein (gm/day) |
| 1. Babies | 10 |
| 2. School-age kids | 15- 35 |
| 3. Teenage age boys | 50- 54 |
| 4. Teenage age girls | 46- 50 |
| 5. Adult men | 56 |
| 6. Adult woman | 48 |
| 7. Pregnant woman | 60 |
| 8. Maternity woman | 71 |
Consequences of protein deficiency in the body
Following are the consequences of protein deficiency in the body as we all know protein is the primary building block of our body hence its deficiency in a diet results in some severe results.
1. Lack of protein impairs the growth of children. Excessive protein deficiency causes two diseases in the children’s body called kwashiorkor and marasmus.
2. In the absence of protein, fat accumulates in the liver to form the fatty liver. The liver fails in plasma albumin synthesis. As a result, oedema or dropsy occurs.
3. Lack of protein does not lead to proper secretion of digestive enzymes from the intestine and various glands. This results in stomach problems and diarrhea occurring due to a lack of digestion and assimilation of food.
4. The absence of protein in food causes muscle wasting and anemia (3) & (6).
Getting the right amount of protein provides nutrition to the human body. Taking large amounts of protein causes contaminants in the body. As a result, headaches, fatigue, and sometimes arthritis disease occur. The human body continues to grow from birth to 25 years. So the need for protein is the highest at this time. Protein universally generates body heat and energy, building and enhancing the body. So the importance of protein in human nutrition is immense.
Written By: Manisha Bharati
References
1. Ajoy Paul. Zoology Honours (volume 1). Books and Allied (P) Ltd., Kolkata (India). Chapter 3: Proteins. Page no: 771 to 792.
2. Chandrasekhar Chakrabarti. A modern approach to a textbook of core Zoology, General & Honours. Nirmala Library, A Publishing House under the Prestigious International Standard Book Number (ISBN) System. Kolkata, (India). Part – II, Chapter 25-carbohydrates, protein & lipid. Page: 2nd -25- 21 to 2nd– 25 – 35.
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