When we prioritize protein as the first and most important of the macronutrients, instead of just including protein-rich foods, we need to understand the quality of protein. So, how do we know this quality in protein food? Let’s see what protein is made up of.
Protein
Protein is essential for regulation of various metabolic processes. It is an indispensable macronutrient in terms of both quantity and quality for humans. Like carbohydrates and fats, proteins don't have any specific storage system in the human body. It needs to be provided through diet, hence daily intake of protein is of utmost importance. To understand about the quality of protein, one has to learn about the components of protein. A protein is made up of small units known as ‘amino acids’. An amino acid is a single or smaller unit of a protein. An amino acid is composed of carbon, hydrogen, oxygen, and nitrogen. The presence of nitrogen is what makes the protein crucial to be consumed from the diet. There are hundreds of amino acids in nature, but only a few are needed by the human body. In humans, there are 20 amino acids that are needed, and every protein made by the body has different combinations of these amino acids. These 20 amino acids are categorized as essential and non-essential amino acids.
Essential amino acids
Essential amino acids (EAAs) are those ‘like in the name ‘essential’ for your body to help make other proteins or hormones that are involved in a variety of metabolic processes or pathways. These are not made by the body, and hence it is necessary to consume from the diet. EAAs are used in the production of many other proteins that are made by the body (endogenous) such as keratin, collagen etc. Many findings show that EAAs are involved in the metabolic health and longevity through these various metabolic processes.
Out of the 20 amino acids, nine are the essential amino acids, which are also called as ‘indispensable amino acids’. These are,
| Phenylalanine |
|---|
| Valine |
| Tryptophan |
| Threonine |
| Isoleucine |
| Methionine |
| Histidine |
| Leucine |
| Lysine |
All the above amino acids are obtained from food that is often told as ‘ complete protein ’ source. Foods that contain all these essential amino acids are majorly from animal sources such as lean meat, poultry except for soy which is a plant origin. A person is recommended to consume a complete protein on a daily basis. Let’s look into each of these essential amino acids and their role in other body processes.
| Essential amino acid | Role/Function |
|---|---|
| Phenylalanine | Production of compounds such as stress hormones, dopamine and other amino acids in nerve tissues |
| Valine | Plays role in muscle protein synthesis – promoting muscle growth and repair |
| Tryptophan | Important in the formation of serotonin and melatonin hormones |
| Threonine | Plays role in the synthesis of structural protein such as enamel on tooth, collagen, elastin. It also plays a role in metabolism of fats. |
| Isoleucine | Plays role in many physiological functions such as immune functions and found mostly in muscle tissues. |
| Methionine | It contains ‘sulfur’ and produces other sulfur containing compounds in the body, that play a role in normal cell function. |
| Histidine | Plays role in protection of nerve cells and is important in immune, gastric and sexual function. |
| Leucine | Plays role in muscle repair and in the production of hemoglobin |
| Lysine | Plays role in structural protein synthesis, immune function and absorption of calcium |
The role of these amino acids are not limited to the mentioned, and they are involved in every other physiological and metabolic functions.
The three essential amino acids, called as Branched-chain amino acids (BCAA) are Leucine, Isoleucine, and Valine. These plays major role in the muscle protein synthesis, repair, and maintenance. It is also said to boost the performance during exercise and help with fatigue. Hence, it is often consumed as supplement. As long as the complete protein sources are consumed, intake of these specific amino acids is not necessary.
BCAAs and methionine are also involved in aging process, longevity and metabolic health in recent findings (Kitada M et al., 2019).
References
- Kitada, M. et al. (2019) ‘The impact of dietary protein intake on longevity and metabolic health’, EBioMedicine, 43, pp. 632–640. doi: 10.1016/J.EBIOM.2019.04.005.
- https://www.ncbi.nlm.nih.gov/books/NBK557845/
- NCBI PubChem
- https://pubchem.ncbi.nlm.nih.gov/compound/L-threonine
