No protein, no life
Protein was discovered by the Dutch scientist Gerardus Johannes Mulder in 1838. He observed that living things cannot survive without protein. Protein is the material basis of all life and an important component of the body's cells. Every tissue in the human body—hair, skin, muscle, bone, internal organs, brain, blood, nerves, etc.—is composed of protein. Therefore, protein plays a very important role in the growth and development of infants and young children. For example, the growth of human brain cells has two peak periods: the first is at 3 months of fetal development; the second is from birth to 1 year old, especially from 0 to 6 months, which is a period of rapid growth of brain cells. By age 1, the proliferation of brain cells is basically complete, with their number reaching 90% of that of an adult, and the driving force for brain cell division is protein.
Protein also plays a very important role in maintaining the normal function of the nervous system, such as taste, vision, and memory. It is also the main raw material for hormones, regulating the physiological activities of various organs in the body. Growth hormone is synthesized from 191 amino acid molecules. If protein intake is insufficient, a baby's physical development will be affected, leading to problems such as stunted growth, anemia, poor intellectual development, and poor vision.
Protein also plays a role in maintaining the body's metabolism and transporting various substances. For example, hemoglobin transports oxygen (red blood cells are renewed at a rate of 2.5 million per second), and lipoproteins transport fat and receptors on cell membranes. Protein is also the main component for synthesizing antibodies. Immune cells and immune proteins, such as white blood cells, lymphocytes, macrophages, antibodies (immunoglobulins), complements, interferons, etc., are renewed every 7 days. When protein is sufficient, this "army" is very strong and can increase 100-fold within hours when needed; if protein intake is insufficient, the baby's immunity will decrease.
Amino acids are the basic units that make up protein
Protein in food must be digested by the gastrointestinal tract and broken down into amino acids before it can be absorbed and utilized by the human body. The human body's need for protein is actually its need for amino acids. Only when the absorbed amino acids meet the body's needs in both quantity and type can the body use them to synthesize its own protein. Therefore, the quality and quantity of food protein and the ratio of various amino acids are related to the amount of protein synthesized by the human body. This is especially true for the growth and development of infants and young children, which is closely related to the quality and quantity of protein in their diet.
In nutrition, amino acids are divided into two categories: essential and non-essential. Essential amino acids are those that the human body cannot synthesize itself or cannot synthesize in sufficient quantities to meet the body's needs, and therefore must be obtained from food. For adults, there are 8 such amino acids, including lysine, methionine, leucine, isoleucine, threonine, valine, tryptophan, and phenylalanine; for infants, there are 9, with an additional one, histidine. Non-essential amino acids do not mean that the human body does not need them, but that the body can synthesize them itself or convert them from other amino acids, so they do not necessarily have to be directly obtained from food. These amino acids include glutamic acid, alanine, glycine, aspartic acid, cystine, proline, serine, and tyrosine, totaling 12.
In nutrition, food proteins are divided into 3 categories based on the types and quantities of amino acids they contain:
★ Complete Protein
This is a high-quality protein that contains all the essential amino acids in sufficient quantities and in appropriate proportions. This type of protein not only maintains human health but also promotes growth and development. The proteins in milk, eggs, fish, and meat are all complete proteins.
★ Semi-complete Protein
Although this type of protein contains all the amino acid types, the quantity of some amino acids does not meet the body's needs. They can sustain life but cannot promote growth and development. For example, gliadin in wheat is a semi-complete protein, as it contains very little lysine.
★ Incomplete Protein
This type of protein cannot provide all the essential amino acids needed by the human body. Relying solely on them, they cannot promote growth and development nor sustain life. For example, collagen in animal skin is an incomplete protein.