Amino acids (AA) had traditionally been classified as nutritionally essential (indispensable) or non-essential (dispensable) for animals and humans. Nutritionally essential AA (EAA) are defined as either those AA whose carbon skeletons cannot be synthesized de novo in animal cells or those that normally are insufficiently synthesized de novo. These AA include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. In contrast, nutritionally non-essential AA (NEAA) are those AA which can be synthesized de novo in adequate amounts by the animal organism to meet requirements for maintenance, growth, development, and health and, therefore, need not be provided in the diet. NEAA include alanine, arginine, asparagine, aspartate, cysteine, glutamate, glutamine, glycine, proline, serine, taurine, and tyrosine.

Although EAA and NEAA had been described for over a century, there are no compelling data to substantiate the assumption that NEAA are synthesized sufficiently in animals and humans to meet the needs for maximal growth and optimal health. Many nutritionists have spent many years in this field and argue strongly that NEAA are indispensable for the metabolic needs and survival of mammals, birds, and fish. For example, many articles from Prof. YIN Yulong抯 group in the Institute of Subtropical Agriculture, Chinese Academy of Sciences (ISA) suggested that NEAA (i.e. arginine, glutamate, glutamine, aspartate, cysteine, and glycine) play important roles in regulating gene expression, cell signaling pathways, digestion and absorption of dietary nutrients, antioxidative responses, and immunity.

Recently, Prof. HOU Yongqing and Prof. YIN collaborated with Prof. WU Guoyao systemic reviewed the biofunctions of NEAA in humans and animals (Fig.1). In this article, the researchers highlighted the metabolic functions of NEAA, including synthesis of peptides and non-peptide substances, regulation of gene expression, regulation of cell signaling pathways, regulation of digestion and absorption of nutrients, energy and nutrient metabolism, immune function, animal and human reproduction, and antioxidative and detoxification reactions.

The researchers wish that this concept represents a new paradigm shift in protein nutrition to guide the feeding of mammals (including livestock), poultry, and fish. So, don't ignore the biofunction of NEAA and be reasonable to arrange your diet! They may make a big contribution in your body.

This review has been published on Exp Biol Med (Maywood). More detail please find at http://www.ncbi.nlm.nih.gov/pubmed/26041391.

YIN Yulong

yinyulong@isa.ac.cn

Institute of Subtropical Agriculture, Chinese Academy of Sciences