What Are Amino Acids?

Amino acids are essential to all living things, from microbes to humans.
All living bodies contain the same 20 amino acids.

Amino acids make up about 20% of our bodies by weight, or about 50% of our solid body mass; they are the next largest component in our bodies after water. The body of a person weighing 50kg contains about 10kg of amino acids.

Amino acids are the building blocks of proteins. There are 100,000 proteins, all made up of just 20 amino acids.

Twenty amino acids make up the proteins in the human body.

Nine of the twenty amino acids cannot be synthesized in our bodies and must therefore be obtained from food. These are the essential or indispensable amino acids. They are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.

The remaining eleven amino acids can be synthesized from other amino acids in the body and are therefore referred to as non-essential or dispensable amino acids. The non-essential amino acids are alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine. However, both essential and non-essential amino acids play an important role in sustaining life.

Some non-essential amino acids (e.g. arginine, cysteine, and tyrosine) are called semi-essential or conditionally essential amino acids because they tend to run low during infancy, or when we are sick or injured, or after surgery.

Amino acids combine to form the proteins that not only make up our bodies but also regulate most of their essential functions. Collagen, keratin, and hemoglobin are just three examples of proteins in the human body.

Amino acids also regulate and maintain our bodily processes by forming enzymes or hormones such as thyroxine, insulin and adrenalin.

Another important function of amino acids is to supply energy to the body. Typically, a healthy body on an average diet uses carbohydrates as a primary source of fuel. However, proteins and amino acids can be used as fuel as a last resort when the primary sources are depleted by rigorous exercise.

Amino acids also play an important role in food flavors. Proteins do not have much flavor in themselves, but each amino acid has a unique flavor, and the combination and ratio of amino acids is one of the most important determinants of food flavor. The best-known amino acid is glutamic acid, which is responsible for umami—savoriness or the “fifth taste”—and is also used in AJI-NO-MOTO® umami seasoning.

Since our bodies cannot synthesize the nine essential amino acids, we have to consume them in our food. A balanced diet providing all the essential amino acids is very important for the proper functioning of our bodies.

Balanced nutrition is important for staying healthy. The human body needs a balanced intake of the five major nutrients—proteins, fats and carbohydrates, plus vitamins and minerals—every day. Guidelines on the recommended daily intake of these nutrients are published by the World Health Organization (WHO) and other international bodies. Failure to maintain a good nutritional balance can raise the risk of obesity and lifestyle-related diseases.

Similarly, reports on daily intake requirements of the nine essential amino acids have been jointly published by the Food and Agriculture Organization of the United Nations (FAO), the World Health Organization (WHO) and the United Nations University (UNU). These reports use “amino acid scores” as a way of assessing the nutritional value of dietary protein.

The amino acid score for a given food indicates the level of each essential amino acid contained in that food, as a ratio (%), in relation to a reference value. Chicken, for example, has an amino acid score of 100, indicating that it is high-quality protein containing an adequate proportion of each of the nine essential amino acids. By contrast, polished white rice has an amino acid score of 65, indicating that it is deficient in certain essential amino acids.

In a protein with an amino acid score of less than 100, the essential amino acid present in the lowest quantity is called the “limiting amino acid.” The nutritional value of a protein can be improved by supplementing the limiting amino acid.

To stay healthy, it is essential to eat a diet with a proper balance of high-quality proteins containing enough of the essential amino acids, which the body cannot synthesize by itself. If essential amino acids are ingested in a proper balance, the body will be able to utilize them all effectively rather than excreting some of them as waste. For each of the nine essential amino acids, there is a recommended daily intake.

The balance of essential amino acids found in foods can be illustrated using the image of a wooden barrel used to hold water. Each stave of the barrel represents a specific essential amino acid. For a food with an ideal balance of amino acids, such as eggs, all the staves of the barrel are the same height, aligning neatly, so the barrel can be filled to the top, indicating that all nine essential amino acids can be utilized in full. In the case of wheat, however, some of the staves are shorter than others, so the barrel can only be filled as high as the shortest stave (corresponding to the limiting amino acid). This represents how a deficiency in one amino acid also limits the available amounts of the other amino acids. Similarly, if even one essential amino acid is missing, the barrel will not hold any water at all, indicating that the other amino acids are now unavailable, so they cannot be utilized, and will simply be excreted as waste.

So, in the case of wheat, let’s consider what happens when the limiting amino acid, lysine, is supplemented. The lysine stave gets taller, allowing the barrel to hold more water, indicating that the other amino acids are also now available in higher amounts, and can be utilized more effectively.

The barrel theory has been used to achieve nutritional improvement in many countries with poor diets, contributing to the solution of social problems. For example, many countries in Africa have been suffering from poor development of infants due to nutritional deficiencies and resulting in high fatality rates.

In Ghana, a traditional millet porridge called “koko” is eaten widely as a complementary food, and often given to infants and young children. However, koko’s amino acid score shows that it does not meet the WHO’s nutrient requirements and dietary recommendations.

To address this nutrient gap, the Ajinomoto Group, in collaboration with various partners, developed KOKO Plus®¹, a supplement containing amino acids and soybean protein, designed to improve nutrition in infants and young children. When added to koko during cooking, KOKO Plus® provides a good balance of essential amino acids along with calcium, iron, zinc, iodine, folic acid, vitamins A, B1, B2, B6, K1, D3, B12, and niacin. In 2018, the World Food Programme (WFP) verified the efficacy of KOKO Plus® and registered it as a “nutritious powder” in its food basket.

^{1    In 2017, the Ajinomoto Group transferred its official partnership role in the Ghana Nutrition Improvement Project to the Ajinomoto Foundation.}

High-lysine foods often featuring in our daily diet include dairy products, eggs, meat, fish, and soybeans. Rice, however, is low in lysine. It is therefore helpful to eat rice in combination with soybean products such as miso and tofu to ensure that we ingest the full complement of essential amino acids. To stay healthy, it is very important to eat a balanced diet covering all the essential amino acids.

The Ajinomoto Group supports the healthy lives of people all around the world by unlocking the power of amino acids. Read more about our approach to Nutrition here.