Amino acid levels following beef protein and amino acid supplement in male subjects.

In the present study the plasma amino acid response of six lean subjects to a protein meal and a commercial amino acid supplement were compared. The amino acid supplement studied was formulated and marketed to be taken after exercise and at other times with the aim of increasing protein synthesis and/or decreasing protein degradation and to lower the ratio of tryptophan to the other large neutral amino acids (LNAA); tyrosine, valine, leucine, isoleucine, phenylalanine and methionine (trp/LNAA), to reduce fatigue. The amino acid supplement administered at the dose recommended by the manufacturer (4 g) was able to bring about a rapid but short-lived (15-30 min) increase in plasma amino acid concentrations and to produce a similarly brief decrease in the trp/LNAA and tyr/LNAA ratios and therefore achieved these aims with respect to amino acid levels even if only briefly. The changes in trp/LNAA and tyr/LNAA ratios after the supplement were of the same order as those produced after the much larger (50 g) protein meal but of shorter duration. However the relatively small insulin response after the amino acid supplement points to a lower level of amino acid uptake by muscle and other tissues for protein synthesis compared to that produced by the beef meal.

A comparison of the effects of beef, chicken and fish protein on satiety and amino acid profiles in lean male subjects.

We compared postprandial satiety and plasma amino acid, insulin, and glucose concentrations in six lean male subjects after the ingestion of three types of protein (beef, chicken and fish). Satiety was greater after the fish meal (P less than 0.01). The observed difference in satiety could be correlated with two of the putative satiety signals measured in this study: 1) serotoninergic activity, due to differences observed in the postprandial tryptophan to large neutral amino acid ratio; and 2) digestibility, reflected in the significantly (P less than 0.05) longer time it took for the plasma amino acid concentrations to peak after the fish meal. Correlations between dietary and plasma amino acid concentrations were determined and good correlations (r = 0.90) were observed for essential amino acids other than lysine and tryptophan. There were no differences in insulin or glucose concentrations in subjects after consuming each of the three meals. Whether other differences that we observed, such as increased concentrations of taurine and methionine following the fish meal, had any effect on satiety or were of biological significance is not known.

Potential regulators of feeding behavior in anorexia nervosa.

We recruited 10 patients with anorexia nervosa and 6 age- and height-matched control subjects. Basal and postprandial concentrations of glucose, insulin, cholesterol, amino acids, gastrin, and pancreatic polypeptide (PP) were measured in response to a standard mixed meal. The only satiety signal that was significantly different between the anorectic group and the control group was PP (P less than 0.001). Tryptophan-LNAA and tyrosine-LNAA ratios were not significantly different in the two groups; however, there was a trend toward a lower tryptophan-LNAA ratio in the anorectic group. Gastrin concentrations were significantly decreased in the anorectic group (P less than 0.001) as were basal insulin concentrations (P less than 0.05). Decreased gastrin concentrations may play a role in the gastric symptoms associated with anorexia nervosa. Previous findings that PP release is diminished in obesity, together with the present findings of PP increase in anorexia nervosa, suggest that this peptide may play a role in appetite control mechanisms.

Quantitation of tryptophan and other plasma amino acids by automated pre-column o-phthaldialdehyde derivatization high-performance liquid chromatography: improved sample preparation.

Pre-column derivatization with o-phthaldialdehyde is a rapid and sensitive method for the quantitation of amino acids in biological fluids. This method uses acetonitrile as a deproteinizing reagent which gives improved recovery of tryptophan compared with 5-sulfosalicylic acid and permits the measurement of aspartic acid which coelutes with 5-sulfosalicylic acid. The method is automated to increase reproducibility and convenience. Mean coefficients of variation for peak areas relative to internal standard were 3.2 and 5.2% for amino acid standards and plasma samples, respectively. The presence of nitrilotriacetic acid stabilized the o-phthaldialdehyde reagent which is important in an automated system. The method is suitable for the analysis of large numbers of plasma samples where total tryptophan and aspartic acid are of interest.