Protein 101 - Types, Key Benefits and Food Sources

Ever wondered why protein is important in our diet? Discover the types of protein, their key benefits and food sources.

Tissue building is the primary function of protein. 

It is an important structural component that’s needed for the formation of cells in your bones, nails, hair and skin. 

An important raw material needed for your body to make enzymes which are essential for its functioning such digestion and reproduction. 

It is involved in the production of neurotransmitters, which influences your mood and mind. 

Protein is also one of the base materials needed in the immune system. (1) 

Life is not possible without protein in your body. 

The human body is a superb packet of more than 100,000 different proteins. (2) 

Since our body is not capable of manufacturing protein, it has to be consumed from our diet on a daily basis to replace the loss ones.

Did you know?

Protein is considered the substance of life? 

The word “protein” originates from a Greek word meaning “first place”. (3) 

Water is the most plentiful substance in the body. 

Second is protein. 

It makes up about 15% to 20% of our body weight. (4) 

In fact, 50% of the body’s dry weight (not including water) is protein, and there are 100,000 of different proteins, each with special functions. (5)

Why Do You Need Protein?

why protein

You need protein for a number of reasons: 

Defense and Immunity

Protein is a major component of leucocytes, or white blood cells, which act against bacteria. 

Therefore, protein is essential to help fight infection and illnesses. 

It is also needed in the formation of antibodies, which increase our immunity to foreign bodies. 

Healthy Skin and Hair

90% of our hair and skin tissue is protein. 

Lack of protein will show up in brittle, fragile hair strands and wrinkled skin.

Energy Levels

Enzymes, which are responsible for converting food into energy, are constructed from protein. 

They are also catalysts for chemical reactions. 

Protein, therefore, has a direct influence on the amount of energy you have. 

It is also the basic material in hormones, which, among other things, impacts our blood sugar levels and metabolic rates. 

Growth and Maintenance

Protein is vital to the development of new and replacement tissues. 

For example, for wounds to heal after a burn or injury, or hair to grow after a trim at the salon, cells and tissues cannot be replaced without protein. 


Protein is responsible for regulating the level of certain substances within the body, namely water. 

As it attracts water, protein helps maintain fluid balance in cells. 

It also helps transport materials such as salt, potassium and electrolytes, in and out of cells. 

A Blood Component

Protein is an important part of red blood cells and plasma, which are essential blood components. 

It is also necessary for the formation of new red blood cells (which have a lifespan of approximately 3 to 4 months). 

In order to perform all these tasks, proteins that are eaten must first be digested or broken down into the smaller units called amino acids. (1)

The Building Blocks of Protein

Although they perform many diverse functions, proteins in all living tissue regardless of their source (animal or plant) are made of 20 different kinds of amino acids, which serves as biochemical building blocks. (6) 

The only difference between different proteins is the number, type and sequence of the amino acids present in the protein chains, as well as the structural configurations. 

Amino acids have the same relationship to proteins as alphabets have to words. 

Just as alphabets combine to form thousands of words, amino acids combine to make thousands of combinations of cell materials, tissues, enzymes, hormones or other active components. 

Essential and Non-Essential Amino Acids

amino acids

The body absorbs protein from food, breaks it down, and reconstructs many of the amino acids. 

Of the 20 known amino acids, 9 are called “essential amino acids” because they cannot be synthesized in sufficient quantities in the body. 

Essential amino acids must be obtained from the food that we eat. 

The nine essential amino acids are histidine, methionine, threonine, tryptophan, leucine, isoleucine, lysine, valine and phenylalanine. 

It is not necessary for you to memorize this entire list of amino acids. :) 

If you eat “complete” proteins, you will have all the essential amino acids you need. 

Histidine and arginine are also essential for infants growth. 

Since essential amino acids are not stored in the body, sources of protein containing them must be included in your daily diets. 

To build the proteins needed for maintenance and growth, all the essential amino acids must be present at the same time. 

If even one is absent or present in too small an amount, this deficiency will limit the utilization of the other amino acids. 

The amino acid which is deficient is known as the “limiting” amino acid, and the principal limiting amino acids are methionine, tryptophan and lysine. 

It is also possible that an excess of one amino acid may reduce the utilization of another amino acid. 

Thus, a deficiency occurs. 

Amino acids cannot be stored for use later on. 

Instead, they are oxidized and the nitrogen portion is excreted, chiefly as urea. 

The carbon, hydrogen and oxygen fragments that are left are used to provide energy or are converted into fat. 

The body does not utilize the energy available in protein unless the other sources of energy (carbohydrates and fats) have already depleted. (7)

“Complete” and “Incomplete” Proteins

complete and incomplete protein

Food containing all eight of the essential amino acids and many of the non-essential ones are called “complete” proteins. 

Those that have essential amino acids in the right proportions are considered to have high biological value. 

“Incomplete” proteins, called low biological value food, on the other hand, usually lack one or more of the key amino acids. 

Meat, fish, eggs and dairy products are examples of complete protein sources. 

Plant food such as vegetables, fruits, nuts and grains are examples of incomplete protein sources. 

Preferred complete protein sources include lean meat, poultry, seafood, skim milk, egg whites, legumes, wholegrain and soy products. 

Liver, whole eggs, whole milk, and most cheeses are also good protein sources, but they should be eaten less frequently, because of their saturated fat and cholesterol content. 

A healthy diet requires that we get an adequate amount of “complete” protein without extra fat and cholesterol. 

In most cases, poultry and fish have lower fat and cholesterol content than fatty red meat like beef and mutton. 

So, a healthy diet demands a balanced combination of animal protein sources such as lean meat and poultry, mixed with plant protein sources such as beans, rice or cereals. 

Protein from plants such as vegetables, grains, beans, peas and lentils, lack one or more essential amino acids, and are considered incomplete proteins. 

However, by combining plant protein from different sources, such as rice with beans or seeds, you can ensure that all the essential amino acids that all the essential amino acids are consumed. (8)

How Much Protein Do You Need?

Protein should account for about 15% of our daily calories and ideally from protein sources that are low in fat. 

Protein requirements vary from person to person depending on individual lean body mass, physical activity, life-stage and age.

Recommended protein intake:

Age Gender Grams/Day
1-3 16
4-6 24
7-10 28
11-14 Boys
15-18 Boys
19-24 Males
Above 25 Males
Source: Food and Nutrition Board, National Research Council, National Academy of Sciences, 10th ed., 1989, National Academy. Press: Washington, DC.

Examples of food and their relative value:

Protein content per 100 grams

Food Protein Content (g) Kcal Energy from Protein (Kcal)
Chicken 23 150 92
Fish 20 100 80
Milk 8 67 32
Peanuts 23 630 92
Rice 7 350 28
Potato 1.6 100 6
Source: Nutrition Facts Desk Reference by Dr. Art Ulene.

At first glance, it may seem that animal sources of protein would be superior because of the higher concentration of protein. 

However, the body cannot distinguish the source of protein nor the concentration – only the total amount. 

Meat may be good protein source but during production, other substances are added to it. 

For example, antibiotics, hormones, pesticides and herbicides have been found in cattle and pig feed. 

Milk is also said to be a good source of protein, but the problems often associated with pasteurization and milk products make it a less than desirable source. 

As it turns out, soy protein has gained much reputation as a good protein source and has proven to have health benefits. 

Furthermore, soy protein comes without the heavy load of fat that is present in meat, eggs and milk. 

Soy protein can also be the alternative for those who are allergic to milk and milk products (lactose intolerant), and to those who prefer protein from non-animal sources (vegetarians). 

Soy contains phytochemicals known as isoflavones, which may play a role in lowering risks for diseases. (9)

Is Your Protein of Good Quality?

is your protein of good quality

It is easy to measure the amount of protein present in food, but measuring the quality of protein – the types and quality of essential amino acids present can be rather complicated. 

One way to estimate the quality of protein is to analyze the essential amino acids and then compare the result to a standard amino acid profile developed by the Food and Agriculture Organization (FAO) and the World Health Organization (WHO). 

This standardized profile is recognized throughout the world. 

The most common biological method of protein comparison is the Protein Efficiency Ratio (PER)

The test protein is compared to milk protein (casein) which has a PER of 2.5. 

So, any protein with a PER of 2.5 or above is considered a high-quality protein. 

Another method, the Biological Value (BV) is more accurate than the PER, but is more tedious to perform. 

One other factor that is important in determining protein quality is the digestibility of the protein – called Protein Digestibility Corrected Amino Acid Score (PDCAAS).

Food PDCAAS Score
Beef 0.92
Kidney Beans 0.68
Rolled Oats 0.57
Wholewheat 0.4
Source: World Health Organization

The World Health Organization (WHO) now uses this new evaluation method to rate the amino acid of the protein, plus a rating of its digestibility by humans. (7) 

  1. The Benefits of Protein. (2020, October 21).
    Retrieved February 26, 2022, from WebMD. Link
  2. M;, M. A. C. J. M. (n.d.). More than 100,000 detectable peptide species elute in single shotgun proteomics runs but the majority is inaccessible to data-dependent LC-MS/MS. Journal of proteome research.
    Retrieved February 26, 2022, from Link
  3. Merriam-Webster. (n.d.). Protein definition & meaning. Merriam-Webster.
    Retrieved February 26, 2022, from Link
  4. Wang, Z. M., Shen, W., Kotler, D. P., Heshka, S., Wielopolski, L., Aloia, J. F., Nelson, M. E., Pierson, R. N., & Heymsfield, S. B. (2003, November 1). Total body protein: A new cellular level mass and distribution prediction model. OUP Academic.
    Retrieved February 26, 2022, from Link 
  5. Proteins. (n.d.).
    Retrieved February 26, 2022, from Link
  6. Zhang, Y., & Gladyshev, V. N. (2007). High content of proteins containing 21st and 22nd amino acids, selenocysteine and pyrrolysine, in a symbiotic deltaproteobacterium of gutless worm olavius algarvensis. Nucleic acids research.
    Retrieved February 26, 2022, from Link 
  7. Who | who/iris - who | world health organization. (n.d.).
    Retrieved February 26, 2022, from Link
  8. 29, N. M. / J. (2020, January 29). Complete vs. incomplete protein sources. BuiltLean.
    Retrieved February 26, 2022, from Link
  9. WebMD. (2000, June 26). How good is soy? WebMD.
    Retrieved February 26, 2022, from Link
Editor at Yeo International
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