Nitrogen balance (NB), the principal methodology used to derive recommendations for human protein and amino acid requirements, has been widely criticised, and calls for increased protein and amino acid requirement recommendations have been made, often on the basis of post-prandial amino acid tracer kinetic studies of muscle protein synthesis, or of amino acid oxidation. This narrative review considers our knowledge of the homeostatic regulation of the FFM throughout the diurnal cycle of feeding and fasting and what can and has been learnt from post-prandial amino acid tracer studies, about amino acid and protein requirements. Within the FFM, muscle mass in well fed weight-stable adults with healthy lifestyles appears fixed at a phenotypic level within a wide range of habitual protein intakes. However homoeostatic regulation occurs in response to variation in habitual protein intake, with adaptive changes in amino acid oxidation which influence the magnitude of diurnal losses and gains of body protein. Post-prandial indicator amino acid oxidation (IAAO) studies have been introduced as an alternative to NB and to the logistically complex 24 h [13C-1] amino acid balance studies, for assessment of protein and amino acid requirements. However, a detailed examination of IAAO studies shows both a lack of concern for homeostatic regulation of amino acid oxidation and  major flaws in their design and analytical interpretation, which seriously constrain their ability to provide reliable values. New ideas and a much more critical approach to existing work is needed if real progress is to be made in the area.

Alcohol abuse causes severe metabolic abnormalities inducing hepatic damage and malnutrition. Since higher Fischer ratio proteins have therapeutic value in liver diseases, an investigation was undertaken to study the ameliorative effect of the enhanced Fischer ratio flaxseed protein hydrolysate (EFR-FPH) alone and in combination with antioxidant micronutrients on ethanol-induced hepatotoxicity in a rat model. The EFR-FPH was prepared by dual enzymatic hydrolysis and charcoal treatment of flaxseed protein. The ratio of the branched-chain:aromatic amino acids (Fischer ratio) was found to be 7·08. The EFR-FPH, characterised using LC-MS/MS, showed the abundance of free leucine and isoleucine compared with phenylalanine and tyrosine. The matrix-assisted laser desorption/ionisation-time of flight MS analysis revealed the larger peptides present in EFR-FPH with mass 2·3 kDa. The EFR-FPH improved the nutritional status, liver function and antioxidant defense in the ethanol hepatotoxicity-induced rat model. The hepatoprotective effect of EFR-FPH was significantly enhanced when combined with selenium or vitamin E. Ethanol-induced changes in the liver tissue were effectively suppressed in the groups receiving EFR-FPH. Flaxseed-based hepatoprotective dietary supplement was formulated incorporating an optimum level of EFR-FPH (10 %) based on sensory acceptability and was fortified with selenium and vitamin E. The hepatoprotective formulation significantly lowered aspartate transaminase, alanine transaminase, alkaline phosphatase and bilirubin by 47, 61, 55 and 78 %, respectively, and improved the antioxidant defense in the ethanol hepatotoxicity-induced rat model. The current investigation suggests that EFR-FPH in synergy with antioxidant micronutrients is potent in ameliorating ethanol-induced hepatotoxicity and has a potential to form a hepatoprotective dietary supplement.

Protein is important for growth, maintenance and protection of the body. Both adequacy of protein quantity and protein quality in the diet are important to guarantee obtaining all the essential amino acids. Protein–energy malnutrition is widely present in developing countries such as Nigeria and might result in stunting and wasting. Needs for protein differ depending on age and physiological status and are higher during growth, pregnancy and lactation. The present review assessed protein quantity and quality in diets of Nigerian infants, children, adolescents, and pregnant and lactating women. Literature reviews and calculations were performed to assess adequacy of Nigerian protein intake and to examine the Nigerian diet. The digestible indispensable amino acid score was used to calculate protein quality of nine Nigerian staple foods and of a mixture of foods. The Nigerian population had mostly adequate protein intake when compared with the most recent protein recommendations by the FAO (2013) and WHO/FAO/UNU (2007). An important exception was the protein intake of adolescent girls and pregnant and lactating women. Most of the assessed Nigerian plant-based staple foods were of low protein quality and predominantly lacked the amino acid lysine. The addition of animal-source foods can bridge the protein quality gap created by predominance of plant-based foods in the Nigerian diet. The methodology of this review can be applied to other low- and middle-income countries where diets are often plant-based and lack variety, which might influence protein intake adequacy.

Ca2+-sensing receptor (CaSR) represents a potential therapeutic target for inflammatory bowel diseases and strongly prefers aromatic amino acid ligands. We investigated the regulatory effects of dietary supplementation with aromatic amino acids – tryptophan, phenylalanine and tyrosine (TPT) – on the CaSR signalling pathway and intestinal inflammatory response. The in vivo study was conducted with weanling piglets using a 2 × 2 factorial arrangement in a randomised complete block design. Piglets were fed a basal diet or a basal diet supplemented with TPT and with or without inflammatory challenge. The in vitro study was performed in porcine intestinal epithelial cell line to investigate the effects of TPT on inflammatory response using NPS-2143 to inhibit CaSR. Dietary supplementation of TPT alleviated histopathological injury and decreased myeloperoxidase activity in intestine challenged with lipopolysaccharide. Dietary supplementation of TPT decreased serum concentration of pro-inflammatory cytokines (IL-1β, IL-6, IL-8, IL-12, granulocyte-macrophage colony-stimulating factor, TNF-α), as well as the mRNA abundances of pro-inflammatory cytokines in intestine but enhanced anti-inflammatory cytokines IL-4 and transforming growth factor-β mRNA levels compared with pigs fed control diet and infected by lipopolysaccharide. Supplementation of TPT increased CaSR and phospholipase Cβ2 protein levels, but decreased inhibitor of NF-κB kinase α/β and inhibitor of NF-κB (IκB) protein levels in the lipopolysaccharide-challenged piglets. When the CaSR signalling pathway was blocked by NPS-2143, supplementation of TPT decreased the CaSR protein level, but enhanced phosphorylated NF-κB and IκB levels in IPEC-J2 cells. To conclude, supplementation of aromatic amino acids alleviated intestinal inflammation as mediated through the CaSR signalling pathway.

Several regimes of supplying exogenous aromatic amino acids to intact, 3-day-old, soybean [Glycine max (L.) Merr. ‘Hill’] seedlings by root uptake were tested to determine if growth retardation caused by root-fed, 0.5 mM glyphosate [N-(phosphonomethyl) glycine] could be reversed. Generally, root-fed levels of aromatic amino acids just below growth-retarding levels (e.g. 1 mM phenylalanine + 0.1 mM tyrosine) reversed root growth inhibition caused by glyphosate to a small (ca. 10%) but significant extent. Feeding aromatic amino acids for 1 to 3 days before glyphosate exposure did not enhance the reversal. Uptake and metabolism of root-fed, aromatic amino acids in control and glyphosate-treated plants were verified by increased levels of hydroxyphenolic compounds (end products of aromatic amino acid metabolism) and by uptake and incorporation of 14C-labeled phenylalanine and tyrosine. On a fresh weight basis, glyphosate had no inhibitory effect on uptake or incorporation of these amino acids into protein or secondary phenolic compounds. After 3 days of exposure, glyphosate had no substantial effects on shikimate dehydrogenase activity in control or aromatic amino acid-fed seedlings. These data suggest that either root-fed aromatic amino acids are compartmentalized differently than the endogenous pools affected by glyphosate or that root-fed glyphosate exerts most of its effect on growth of soybean seedlings through means other than inhibition of aromatic amino acid synthesis.

With the discovery of Na-sulphate minerals on Mars and Europa, recent studies using these minerals have focused on their ability to assist in the detection of bio/organic signatures. This study further investigates the ability of thenardite (Na2SO4) to effectively facilitate the ionization and identification of aromatic amino acids (phenylalanine, tyrosine and tryptophan) using a technique called geomatrix-assisted laser desorption/ionization in conjunction with a Fourier transform ion cyclotron resonance mass spectrometry. This technique is based on the ability of a mineral host to facilitate desorption and ionization of bio/organic molecules for detection. Spectra obtained from each aromatic amino acid alone and in combination with thenardite show differences in ionization mechanism and fragmentation patterns. These differences are due to chemical and structural differences between the aromatic side chains of their respective amino acid. Tyrosine and tryptophan when combined with thenardite were observed to undergo cation-attachment ([M+Na]+), due to the high alkali ion affinity of their aromatic side chains. In addition, substitution of the carboxyl group hydrogen by sodium led to formation of [M-H+Na]Na+ peaks. In contrast, phenylalanine mixed with thenardite showed no evidence of Na+ attachment. Understanding how co-deposition of amino acids with thenardite can affect the observed mass spectra is important for future exploration missions that are likely to use laser desorption mass spectrometry to search for bio/organic compounds in extraterrestrial environments.