In this blog post, we will look at why essential amino acids, which are important for protein synthesis and metabolism in the body, must be supplemented through food.
Our bodies constantly repeat the process of synthesizing and breaking down proteins. Protein synthesis is the process of linking amino acids to form long chains, and about 20 amino acids are used for protein synthesis in the body. In protein synthesis, amino acids are combined in a specific order according to the information contained in the DNA base sequence. At this point, mRNA, which transmits DNA information, tRNA, which transports amino acids, and ribosomes play important roles. Ribosomes read the codons of mRNA and combine the amino acids bound to tRNA in the correct order to form proteins. This process is a biochemical mechanism essential for life and forms the basis of cell structure and function. Protein degradation is the process of breaking down the bonds between amino acids and separating them into individual amino acids. Protein degradation in the body prevents the accumulation of old and damaged proteins and replenishes energy and glucose that our bodies lack.
Proteolysis, which is one of the processes of protein degradation, is carried out inside cells by an enzyme complex called proteasome. Proteasome breaks down proteins that are bound to a certain amount of a substance called ubiquitin into amino acids. About 75% of the amino acids produced through protein degradation are used to synthesize other proteins, and the remaining amino acids are broken down. When amino acids are broken down, the amino groups are separated from the amino acids and converted into ammonia, which is then synthesized into urea and excreted from the body. The remaining parts, after the amino groups have been removed, are used to produce energy or glucose when there is a shortage of these, or else they are synthesized into fatty acids or excreted from the body.
Despite the continuous breakdown of proteins, the total amount of protein in the body can be maintained or increased because protein synthesis occurs constantly within cells. The amino acids necessary for protein synthesis are synthesized within cells, obtained from proteins ingested in food, or produced during the breakdown of proteins in the body. Among the amino acids necessary for protein synthesis, those that cannot be synthesized in the body and cannot be obtained from food are called essential amino acids. The ratio of each essential amino acid required for protein synthesis is fixed. Essential amino acids produced through the breakdown of proteins in the body are also used for protein synthesis, but if the deficient amount is not supplied from external sources, the total amount of protein synthesis in the body will decrease. Therefore, essential amino acids must be obtained through food.
However, unlike adults, children in their growth period cannot synthesize all amino acids in their bodies, so some amino acids that can be synthesized in the body but in insufficient amounts must be supplemented through food. The amount of essential amino acids contained in each food varies, and the more balanced the essential amino acids are, the higher the utilization efficiency of essential amino acids, which is the ratio of the amount used for protein synthesis to the total amount of essential amino acids supplied.
In general, animal proteins such as meat and eggs contain a balanced amount of essential amino acids and have high essential amino acid utilization efficiency, while plant proteins such as rice and beans contain limiting amino acids and have relatively low essential amino acid utilization efficiency. For this reason, it is important for people who mainly consume plant proteins to eat a variety of foods to balance their essential amino acids. For example, eating rice and beans together can complement each other’s limiting amino acids and increase overall protein synthesis efficiency.
Limiting amino acids refer to essential amino acids that are present in the lowest ratio of any food source relative to the amount of each essential amino acid required for protein synthesis. For example, suppose that 2 moles of essential amino acid A and 1 mole of essential amino acid B are required to synthesize 1 mole of a hypothetical protein P. When attempting to synthesize 2 moles of P, if 2 moles of A and 2 moles of B are supplied, there will be a shortage of 2 moles of A compared to the required amount, and only 1 mole of P will be synthesized. In this case, A becomes a limiting amino acid because the amount of protein that can be synthesized is limited due to the shortage of A. Understanding this principle is helpful in evaluating the nutritional value of proteins and creating a balanced diet.
In addition, recent studies on protein intake show that protein synthesis efficiency can vary depending on the type of protein and the timing of intake. Some studies have shown that consuming protein immediately after exercise is more effective for muscle synthesis, which is important information for athletes and people who want to increase muscle mass. Adequate protein intake plays an important role not only in maintaining health but also in improving physical fitness and strengthening the immune system.
As such, protein synthesis and breakdown in our bodies go beyond simply providing energy and nutrients; they are essential processes for maintaining life and health. Therefore, proper protein intake and a balanced diet are important factors directly linked to our health. With this understanding, we will be able to lead healthier lives.
