The genes involved in amino acid metabolisms and biosyntheses tend to have deteriorated, rather than evolved, over time in relation to living and feeding habits of organisms. The essential amino acids are basically the same among diverse animals, suggesting that they were determined at the time of emergence of animals. The presence of the animal essential amino acids has resulted from deterioration of genes that became dispensable in relation to environments. A good example is provided with the nearly complete complementary sets of essential amino acids between hosts and symbionts. We discuss evolutionary characteristics of enzymes or receptor molecules for amino acids that act as neurotransmitters and taste stimuli. We also argue these characteristic features during human evolution.
Nomenclature of “essential” and “nonessential” amino acids has been argued, because the term “nonessential” is not accurate from biochemical and nutritional point of view. Essentiality of amino acids is mainly dependent on the carbon skeleton. Some nonessential amino acids become indispensable in certain disease states or certain developmental stage. Essential amino acids are synthesized through longer steps of enzyme reaction than nonessential amino acids in prokaryote. This may be a major reason that the ability of essential amino acids synthesis has been lost in some species including human. Although prokaryote, plants and fungi are able to synthesize all amino acids, animals and some of protozoa lose the ability of synthesis of essential amino acids. The origin of essential amino acid occurred during the evolution from protozoa to metazoa.
The content of fatty acid (FA) and choline derived from choline phospholipid (choline-choline PL) was measured in school lunches and snacks from two nurseries. Nursery A had eliminated egg, milk, soybean, wheat, and oily fish from their food, whereas nursery B had eliminated only egg, milk and soybean. The mean FA content of the lunches from both nurseries was approximately 9.0 g. In lunches with fish as the main dish, the mean FA content was 5.2 g for nursery A and 6.8 g for nursery B. When meat was the main dish, the mean FA content was higher: 10.8 g for nursery A and 9.9 g for nursery B. In lunches with fish as the main dish, the sum of icosapentaenoic acid (IPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA) was 0.1 g at nursery A and 0.6 g at nursery B. In lunches with meat as the main dish, the sum of IPA, DPA and DHA was less than 0.05 g at both nurseries. The mean content of choline-choline PL in lunches was 29.8 mg at nursery A and 23.5 mg at nursery B. These values for FA, IPA, and DHA are considerably lower than the recommended daily allowances, which highlights the importance of communication with dietitians and parents so that they can provide appropriate nutritional guidance for children.