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Proteins; Functions in the Body, Quality and Daily Needs

Roles and Functions of Proteins in the Body

1. Proteins are the building blocks of the cell, which is the smallest living unit of living organisms.

2. Proteins are involved in the structure of body tissues. They are used in the repair of tissues.

3. All enzymes and most hormones have proteins in their structure.

4. Proteins have transport and storage functions in the body. While hemoglobin and myoglobin carry oxygen, transferrin carries iron in the blood. It provides the storage of iron in the liver.

5. Proteins are a critical element of the immune system. Antibodies produced against foreign substances entering the body are composed of protein.

6. Proteins provide movement and support to the body.

7. Proteins provide impulse formation and transmission in the nervous system.

8. Proteins provide control of metamorphosis and growth in the body.

9. Proteins are not the body’s primary energy source, but they can also be used as an energy source when the body does not have enough energy sources. The body’s primary source of energy is carbohydrates.

Essential Amino Acids

The building blocks of proteins are amino acids. The existence of nearly 200 different amino acids has been identified so far. Generally, 20 of them are included in the structure of proteins. These amino acids are;

amino acids
Amino acids

12 of these amino acids can be produced in the human body. However, eight amino acids cannot be produced in the body. These amino acids, which cannot be made in the body and must be taken from foods, are called “essential amino acids”;

essential amino acids
Essential amino acids

Arginine and histidine are also known to be essential amino acids for babies.

Protein Quality in Foods

Proteins are produced according to the codes in DNA. So, The protein structure of every living organism is different from the others. In other words, proteins are unique for each living organism.

Therefore, the proteins in foods also differ according to their source organism. The quality of the protein evaluates protein’s benefits in terms of nutrition. The quality of a protein is related to its biological value and digestibility of the protein.

The amino acid profile generally determines the biological value of proteins. Digestibility is determined by the amount of nitrogen absorbed from the intestines after the individual consumes that protein.

protein quality
protein quality of foods

In terms of biological value and digestibility, animal protein sources are superior to plant protein sources.

Eggs are the food with the highest quality protein. An average egg weighs 50 grams and contains about 7 grams of protein.

Milk is food as valuable as eggs in terms of quality protein sources. A glass of milk contains about 8 grams of protein. There are approximately 9 grams of protein in 150 grams of yogurt. There are approximately 20 grams of protein in 100 grams of feta.

Among the cheese types, curd cheese produced from whey is superior to cheeses such as feta and cheddar in terms of protein quality.

Because while curd cheese made from whey usually contains serum proteins, the main protein of other types of cheese is casein. The biological value of milk serum proteins is higher than casein, another protein fraction found in milk.

Meat proteins contain all the amino acids an individual needs. One hundred grams of beef contains an average of 21 grams of protein.

Chicken meat and fish meat also have similar protein quality to beef. However, fish meat can be digested faster.

In addition to its amino acid profile, fish meat also has a privileged place in terms of fatty acid profile. Fish meat is also an important source of essential fatty acids.

Plant foods have a lower value than animal foods in terms of protein quality. The most important plant protein source foods are; legumes 27-41% (beans, chickpeas, peas, etc.), cereals 8-12% (wheat, rice, etc.) and oilseeds such as peanuts (25%). Fruits usually have less than 1% protein.

If plant foods are evaluated in terms of the essential amino acids they contain;

  • Legumes are poor in methionine,
  • Cereals are usually poor in lysine,
  • Corn is poor in lysine and tryptophan,
  • Peanuts are poor in lysine, tryptophan, methionine and threonine.

How Much Protein Should You Consume Per Day?

Daily protein requirements can be determined in two different ways.

1. According to body weight

A healthy individual needs to consume 0.75 grams of protein per kilogram of body weight daily to sustain life activities (weight kg x 0.75 grams). For example, an individual weighing 60 kg should consume approximately 45 g of protein per day.

2. According to the number of calories consumed per day

Another way to determine the daily protein requirement is to determine the protein requirement based on the calories consumed. It is recommended that 15% of the calories consumed come from protein.

For example, an individual who spends 2000 calories a day should provide 15% (300 calories) of these calories from protein. Considering that 1 gram of protein provides four calories, the daily protein requirement of this individual is 75 grams.

It should be noted that both calculation methods were performed on healthy adult individuals. The body’s protein requirement naturally increases in young, infants and in cases such as illness/injury. Similarly, individuals engaged in sports need more protein consumption for muscle development.

However, it should be noted that proteins from animal sources have higher biological value and higher digestion rates than proteins from plant sources.

Consuming excessive amounts of protein can cause some problems in the body, such as;

1. Disorders such as “amino acid antagonism” and “toxicity”,

2. The excess protein is converted into fat in the body and the adipose tissue increases,

3. Especially in athletes, removing uric acid from the body can cause experiencing a large amount of water loss in the body

4. It can cause an increase in calcium excretion.


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