Plasma amino acid responses in humans to evening meals of differing nutritional composition

Green Synthesis of a Molecularly Imprinted Polymer Based on a Novel Thiophene-Derivative for Electrochemical Sensing

An environmentally friendly and sustainable approach was adopted to produce a molecularly imprinted polymer (MIP) via electropolymerization, with remarkable electrochemical sensing properties, tested in tyrosine (tyr) detection. The 2,2'-bis(2,2'-bithiophene-5-yl)-3,3'-bithianaphtene (BT2-T4) was chosen as functional monomer and MIP electrosynthesis was carried out via cyclic voltammetry on low-volume (20 μL) screen-printed carbon electrodes (C-SPE) in ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ((BMIM) TFSI). An easy and rapid washing treatment allowed us to obtain the resulting MIP film, directly used for tyr electrochemical detection, carried out amperometrically. The sensor showed a linear response in the concentration range of 15-200 μM, with LOD of 1.04 µM, LOQ of 3.17 μM and good performance in selectivity, stability, and reproducibility. Tyrosine amperometric detection was also carried out in human plasma, resulting in a satisfactory recovery estimation. The work represents the first use of BT2-T4 as a functional monomer for the production of a molecularly imprinted polymer, with a green approach afforded by using a few microliters of a room temperature ionic liquid as an alternative to common organic solvents on screen-printed carbon electrodes, resulting in a valuable system that meets the green chemistry guidelines, which is today an essential criterion in both research and application field.

Greater plasma essential amino acids and lower 3-methylhistidine with higher protein intake during endurance training: a randomised control trial

Endurance exercise alters amino acid (AA) metabolism that necessitates greater AA intake in the post exercise recovery period to support recovery. Thus, daily AA ingestion during a period of endurance training may affect the metabolically active plasma free AA pool, which is otherwise maintained during periods of inadequate protein intake by the breakdown of skeletal muscle proteins. Nine endurance-trained males completed a 4-day running protocol (20 km, 5 km, 10 km and 20 km on days 1-4, respectively) on three occasions with a controlled diet providing different protein intakes [0.94(LOW), 1.20(MOD) or 1.83gprotein kgbody mass-1 day-1 (HIGH)]. Urine collected over 24 h on day-4 and plasma collected after an overnight fast on day-5 were analyzed for free AA (plasma) and 3-methylhistidine (3MH; plasma and urine), a marker of myofibrillar protein breakdown. There was an effect of protein intake (HIGH > MOD/LOW; P < 0.05) on fasted plasma essential AA, branched chain AA and 3MH but no effect on 24-h urinary 3-MH excretion. Consuming a previously determined optimal daily protein intake of 1.83 g kg-1 day-1 during endurance training maintains fasted plasma free AA and may attenuate myofibrillar protein catabolism, although this latter effect was not detected in 24-h urinary excretion. The maintenance of the metabolically active free plasma AA pool may support greater recovery from exercise and contribute to the previously determined greater whole-body net protein balance in this athletic population. TRN: NCT02801344 (June 15, 2016).

Advantages of Studying the Metabolome in Response to Mixed-Macronutrient Challenges and Suggestions for Future Research Designs

Evaluating the postprandial response to a dietary challenge containing all macronutrients-carbohydrates, lipids, and protein-may provide stronger insights of metabolic health than a fasted measurement. Metabolomic profiling deepens the understanding of the homeostatic and adaptive response to a dietary challenge by classifying multiple metabolic pathways and biomarkers. A total of 26 articles were identified that measure the human blood metabolome or lipidome response to a mixed-macronutrient challenge. Most studies were cross-sectional, exploring the baseline and postprandial response to the dietary challenge. Large variations in study designs were reported, including the macronutrient and caloric composition of the challenge and the delivery of the challenge as a liquid shake or a solid meal. Most studies utilized a targeted metabolomics platform, assessing only a particular metabolic pathway, however, several studies utilized global metabolomics and lipidomics assays demonstrating the expansive postprandial response of the metabolome. The postprandial response of individual amino acids was largely dependent on the amino acid composition of the test meal, with the exception of alanine and proline, 2 nonessential amino acids. Long-chain fatty acids and unsaturated long-chain acylcarnitines rapidly decreased in response to the dietary challenges, representing the switch from fat to carbohydrate oxidation. Studies were reviewed that assessed the metabolome response in the context of obesity and metabolic diseases, providing insight on how weight status and disease influence the ability to cope with a nutrient load and return to homeostasis. Results demonstrate that the flexibility to respond to a substrate load is influenced by obesity and metabolic disease and flexibility alterations will be evident in downstream metabolites of fat, carbohydrate, and protein metabolism. In response, we propose suggestions for standardization between studies with the potential of creating a study exploring the postprandial response to a multitude of challenges with a variety of macronutrients.

Association between plasma α-aminobutyric acid and depressive symptoms in older community-dwelling adults in Japan

AIM

To examine the association between depressive symptoms and plasma amino acid related metaboli in older adults.

METHODS

A total of 152 older adults aged ≥65 years, residing in Niigata, Japan, were used for analysis. We evaluated depressive symptoms using the Geriatric Depression Scale-15, which has been validated in older community-dwelling individuals, and used a cut off score of ≥5 to classify participants as having depressive symptoms. We used high-performance liquid chromatography-electrospray ionization mass spectrometry to measure the concentrations of plasma amino acid-related metabolites, and carried out logistic regression analysis to assess the association between depressive symptoms and plasma amino acid-related metabolites.

RESULTS

Of the 119 older adults (mean age 76.3 years) included in the analysis, 22 were classified as having depressive symptoms (depressive group). There were no significant differences in physical and cognitive impairments between participants in the depressive and non-depressive groups. The plasma α-aminobutyric acid (AABA) level was significantly lower in the depressive group than in the non-depressive group (P < 0.001). Logistic regression analysis showed the best-fit model, which included AABA, leucine, threonine, hydroxyl proline and histidine levels (area under the receiver operating characteristic curve 0.8346; 95% confidence interval 0.7365-0.9326). In particular, the plasma AABA level was strongly associated with depressive symptoms.

CONCLUSIONS

Plasma AABA level is significantly associated with depression symptoms in older community-dwelling adults in Japan. Thus, plasma AABA might serve as a potential marker of depression in older adults aged ≥65 years. Geriatr Gerontol Int 2019; 19: 254-258.

Investigation of metabolites for estimating blood deposition time

Trace deposition timing reflects a novel concept in forensic molecular biology involving the use of rhythmic biomarkers for estimating the time within a 24-h day/night cycle a human biological sample was left at the crime scene, which in principle allows verifying a sample donor’s alibi. Previously, we introduced two circadian hormones for trace deposition timing and recently demonstrated that messenger RNA (mRNA) biomarkers significantly improve time prediction accuracy. Here, we investigate the suitability of metabolites measured using a targeted metabolomics approach, for trace deposition timing. Analysis of 171 plasma metabolites collected around the clock at 2-h intervals for 36 h from 12 male participants under controlled laboratory conditions identified 56 metabolites showing statistically significant oscillations, with peak times falling into three day/night time categories: morning/noon, afternoon/evening and night/early morning. Time prediction modelling identified 10 independently contributing metabolite biomarkers, which together achieved prediction accuracies expressed as AUC of 0.81, 0.86 and 0.90 for these three time categories respectively. Combining metabolites with previously established hormone and mRNA biomarkers in time prediction modelling resulted in an improved prediction accuracy reaching AUCs of 0.85, 0.89 and 0.96 respectively. The additional impact of metabolite biomarkers, however, was rather minor as the previously established model with melatonin, cortisol and three mRNA biomarkers achieved AUC values of 0.88, 0.88 and 0.95 for the same three time categories respectively. Nevertheless, the selected metabolites could become practically useful in scenarios where RNA marker information is unavailable such as due to RNA degradation. This is the first metabolomics study investigating circulating metabolites for trace deposition timing, and more work is needed to fully establish their usefulness for this forensic purpose.

Application of Pre-Column Labeling Liquid Chromatography for Canine Plasma-Free Amino Acid Analysis

Plasma-free amino acid (PFAA) levels are a useful metric for diagnosing cancer and providing a prognosis. However, the use of analysis of PFAA levels has been limited in the veterinary medicine field. We addressed the application of liquid chromatography (LC) using a pre-column labeling technique for analysis of canine PFAA levels. This method significantly shortened the analysis time relative to conventional methods. No diurnal fluctuations were detected at 9:00 AM in most PFAA levels, and food intake increased the levels of some PFAAs, including valine, leucine, tyrosine, phenylalanine, and proline. These results indicate that LC with pre-column labeling is useful for measuring canine PFAA levels, for which time of day and interval after food intake must be taken into consideration.

A Novel Multivariate Index for Pancreatic Cancer Detection Based On the Plasma Free Amino Acid Profile

Background

The incidence of pancreatic cancer (PC) continues to increase in the world, while most patients are diagnosed with advanced stages and survive <12 months. This poor prognosis is attributable to difficulty of early detection. Here we developed and evaluated a multivariate index composed of plasma free amino acids (PFAAs) for early detection of PC.

Methods

We conducted a cross-sectional study in multi-institutions in Japan. Fasting plasma samples from PC patients (n = 360), chronic pancreatitis (CP) patients (n = 28), and healthy control (HC) subjects (n = 8372) without apparent cancers who were undergoing comprehensive medical examinations were collected. Concentrations of 19 PFAAs were measured by liquid chromatography–mass spectrometry. We generated an index consisting of the following six PFAAs: serine, asparagine, isoleucine, alanine, histidine, and tryptophan as variables for discrimination in a training set (120 PC and matching 600 HC) and evaluation in a validation set (240 PC, 28 CP, and 7772 HC).

Results

Several amino acid concentrations in plasma were significantly altered in PC. Plasma tryptophan and histidine concentrations in PC were particularly low, while serine was particularly higher than that of HC. The area under curve (AUC) based on receiver operating characteristic (ROC) curve analysis of the resulting index to discriminate PC from HC were 0.89 [95% confidence interval (CI), 0.86–0.93] in the training set. In the validation set, AUCs based on ROC curve analysis of the PFAA index were 0.86 (95% CI, 0.84–0.89) for all PC patients versus HC subjects, 0.81 (95% CI, 0.75–0.86) for PC patients from stage IIA to IIB versus HC subjects, and 0.87 (95% CI, 0.80–0.93) for all PC patients versus CP patients.

Conclusions

These findings suggest that the PFAA profile of PC was significantly different from that of HC. The PFAA index is a promising biomarker for screening and diagnosis of PC.

Diabetes risk and amino acid profiles: cross-sectional and prospective analyses of ethnicity, amino acids and diabetes in a South Asian and European cohort from the SABRE (Southall And Brent REvisited) Study

AIMS/HYPOTHESIS

South Asian individuals have an increased risk of diabetes compared with Europeans that is unexplained by obesity and traditional or established metabolic measures. Circulating amino acids (AAs) may provide additional explanatory insights. In a unique cohort of European and South Asian men, we compared cross-sectional associations between AAs, metabolic and obesity traits, and longitudinal associations with incident diabetes.

METHODS

Nuclear magnetic spectroscopy was used to measure the baseline (1988-1991) levels of nine AAs in serum samples from a British population-based cohort of 1,279 European and 1,007 South Asian non-diabetic men aged 40-69 years. Follow-up was complete for 19 years in 801 European and 643 South Asian participants.

RESULTS

The serum concentrations of isoleucine, phenylalanine, tyrosine and alanine were significantly higher in South Asian men, while cross-sectional correlations of AAs with glycaemia and insulin resistance were similar in the two ethnic groups. However, most AAs were less strongly correlated with measures of obesity in the South Asian participants. Diabetes developed in 227 (35%) South Asian and 113 (14%) European men. Stronger adverse associations were observed between branched chain and aromatic AAs and incident diabetes in South Asian men. Tyrosine was a particularly strong predictor of incident diabetes in South Asian individuals, even after adjustment for metabolic risk factors, including obesity and insulin resistance (adjusted OR for a 1 SD increment, 1.47, 95% CI 1.17,1.85, p = 0.001) compared with Europeans (OR 1.10, 0.87, 1.39, p = 0.4; p = 0.045 for ethnicity × tyrosine interaction).

CONCLUSIONS/INTERPRETATION

Branched chain and aromatic AAs, particularly tyrosine, may be a focus for identifying novel aetiological mechanisms and potential treatment targets for diabetes in South Asian populations and may contribute to their excess risk of diabetes.

Effect of sleep deprivation on the human metabolome

Sleep restriction and circadian clock disruption are associated with metabolic disorders such as obesity, insulin resistance, and diabetes. The metabolic pathways involved in human sleep, however, have yet to be investigated with the use of a metabolomics approach. Here we have used untargeted and targeted liquid chromatography (LC)/MS metabolomics to examine the effect of acute sleep deprivation on plasma metabolite rhythms. Twelve healthy young male subjects remained in controlled laboratory conditions with respect to environmental light, sleep, meals, and posture during a 24-h wake/sleep cycle, followed by 24 h of wakefulness. Two-hourly plasma samples collected over the 48 h period were analyzed by LC/MS. Principal component analysis revealed a clear time of day variation with a significant cosine fit during the wake/sleep cycle and during 24 h of wakefulness in untargeted and targeted analysis. Of 171 metabolites quantified, daily rhythms were observed in the majority (n = 109), with 78 of these maintaining their rhythmicity during 24 h of wakefulness, most with reduced amplitude (n = 66). During sleep deprivation, 27 metabolites (tryptophan, serotonin, taurine, 8 acylcarnitines, 13 glycerophospholipids, and 3 sphingolipids) exhibited significantly increased levels compared with during sleep. The increased levels of serotonin, tryptophan, and taurine may explain the antidepressive effect of acute sleep deprivation and deserve further study. This report, to our knowledge the first of metabolic profiling during sleep and sleep deprivation and characterization of 24 h rhythms under these conditions, offers a novel view of human sleep/wake regulation.

L-Tryptophan: Biochemical, nutritional and pharmacological aspects

Tryptophan is important both for protein synthesis and as a precursor of niacin, serotonin and other metabolites. Tryptophan is an unusual amino acid because of the complexity of its metabolism, the variety and importance of its metabolites, the number and diversity of the diseases it is involved in, and because of its use in purified form as a pharmacological agent. This review covers the metabolism of tryptophan, its presence in the diet, the disorders associated with low tryptophan levels due to low dietary intake, malabsorption, or high rates of metabolism, the therapeutic effects of tryptophan and the side effects of tryptophan when it is used as a drug including eosinophilia myalgia syndrome.

The overnight effect of dietary energy balance on postprandial plasma free amino acid (PFAA) profiles in Japanese adult men

The plasma free amino acid (PFAA) profile is affected by various nutritional conditions, such as the dietary energy balance. Regarding the clinical use of PFAA profiling, it is of concern that differences in food ingestion patterns may generate systematic errors in a plasma amino acid profile and constitute a confounding factor in assessment. In this study, the overnight impact of the dietary energy balance on the postprandial plasma amino acid profile was investigated to elucidate in particular the effects of high protein meals typical in Japanese cuisine. We conducted diet-controlled, crossover trials in eleven healthy male volunteers aged 40-61 y. They consumed either a normal meal (meal N) or high protein meal (meal H) at dinner. Forearm venous blood was collected, and plasma amino acid concentrations were measured before dinner and the next morning. We found that a high protein meal in the evening that contained 40% energy would significantly increase the PFAA concentration the next morning, even more than 12 hours after the meal. Among amino acids, the most significant difference was observed in the branched-chain amino acids (BCAAs) and in some urea-cycle related compounds. If the subject consumed the high protein diet at dinner, the PFAA profile after overnight fasting might be still affected by the meal even 12 hours after the meal, suggesting that the PFAA profile does not reflect the subject's health condition, but rather the acute effect of high protein ingestion.

Relationship between postprandial metabolomics and colon motility in children with constipation

BACKGROUND

The metabolic pathways associated with colonic motility are unknown. To identify potential metabolic targets for treatment of constipation, we examined the metabolic profile before and after a meal challenge in a cohort of children with constipation and determined its relationship with postprandial colon motility patterns.

METHODS

In this prospective study, 187 metabolites were measured by liquid chromatography-mass spectrometry at multiple time points before and after a standardized meal in constipated children undergoing a colon manometry. Postprandial metabolite levels were compared with baseline and also correlated with multiple manometric measurements, including the number, frequency, and amplitude of pressure peaks as well as the motility index (MI).

KEY RESULTS

A total of 20 subjects were included (mean age 13.1 ± 3.4 years). No significant metabolite changes were observed at 10 min after the meal, whereas 16 amino acid and 22 lipid metabolites had significant (P < 0.005) postprandial changes, including decreases in methylhistamine, histamine, and GABA, by 60 min. Correlations were observed between normal and abnormal postprandial motility patterns and changes in specific metabolites, including glycerol, carnosine, alanine, asparagine, cytosine, choline, phosphocholine, thyroxine, and triiodothyronine. Interestingly, subjects without the normal postprandial increase in area under the curve (AUC), had markedly increased levels of kynurenic acid and adenosyl-homocysteine.

CONCLUSIONS & INFERENCES

This is the first study to examine postprandial metabolic changes in children and also to correlate changes in specific metabolites with colonic motility. The results suggest possible metabolic pathways associated with motility and identify potential targets for the treatment of constipation.

Vitamin B6 status and interferon-γ-mediated immune activation in primary hyperparathyroidism

OBJECTIVES

Primary hyperparathyroidism (PHPT) has been associated with low-grade inflammation and elevated risk of cardiovascular disease (CVD). In inflammatory conditions, interferon-γ (IFN-γ) activity is enhanced and a decreased circulating concentration of vitamin B6 is often observed. Such changes in IFN-γ activity or vitamin B6 levels have been associated with increased incidence of CVD. The aim of the study was to investigate systemic markers of IFN-γ-mediated immune activation, such as neopterin, the kynurenine-to-tryptophan ratio (KTR) and kynurenine pathway metabolites, as well as B6 vitamers in patients with PHPT.

DESIGN/SUBJECTS

A total of 57 patients with PHPT and a control group of 20 healthy blood donors were included in this study. PHPT patients who responded positively to parathyroidectomy were followed for 6 months. Forty-three patients participated in the longitudinal study in which blood samples were taken at inclusion and 1, 3 and 6 months after surgery.

RESULTS

Plasma concentrations of the B6 vitamers pyridoxal 5'-phosphate (PLP) (P = 0.007) and pyridoxal (P = 0.013) were significantly lower in the patient group compared to healthy control subjects. An increase in the KTR indicated that the kynurenine pathway of tryptophan metabolism was altered in PHPT patients (P = 0.015). During the initial 6 months after surgery, levels of PLP (P < 0.001) and anthranilic acid (P < 0.001) increased significantly, whereas neopterin decreased (P = 0.018).

CONCLUSIONS

The results of this study demonstrate altered levels of vitamin B6 and the KTR in PHPT patients, both of which may reflect cellular immune activation. These abnormalities should be considered in relation to the increased risk of CVD previously observed in patients with PHPT.

Large neutral amino acids: dietary effects on brain neurochemistry and function

The ingestion of large neutral amino acids (LNAA), notably tryptophan, tyrosine and the branched-chain amino acids (BCAA), modifies tryptophan and tyrosine uptake into brain and their conversion to serotonin and catecholamines, respectively. The particular effect reflects the competitive nature of the transporter for LNAA at the blood-brain barrier. For example, raising blood tryptophan or tyrosine levels raises their uptake into brain, while raising blood BCAA levels lowers tryptophan and tyrosine uptake; serotonin and catecholamine synthesis in brain parallel the tryptophan and tyrosine changes. By changing blood LNAA levels, the ingestion of particular proteins causes surprisingly large variations in brain tryptophan uptake and serotonin synthesis, with minimal effects on tyrosine uptake and catecholamine synthesis. Such variations elicit predictable effects on mood, cognition and hormone secretion (prolactin, cortisol). The ingestion of mixtures of LNAA, particularly BCAA, lowers brain tryptophan uptake and serotonin synthesis. Though argued to improve physical performance by reducing serotonin function, such effects are generally considered modest at best. However, BCAA ingestion also lowers tyrosine uptake, and dopamine synthesis in brain. Increasing dopamine function in brain improves performance, suggesting that BCAA may fail to increase performance because dopamine is reduced. Conceivably, BCAA administered with tyrosine could prevent the decline in dopamine, while still eliciting a drop in serotonin. Such an LNAA mixture might thus prove an effective enhancer of physical performance. The thoughtful development and application of dietary proteins and LNAA mixtures may thus produce treatments with predictable and useful functional effects.

Follow up of phenylketonuria patients

In recent years our understanding of the follow up policies for PKU has increased substantially. In particular, we now understand the importance of maintaining control of blood phenylalanine (phe) concentrations life-long to achieve the best long-term neuropsychological outcomes. The concordance with the follow up strategy remains a key challenge for the future, especially with respect to adolescents and young adults. The recent therapies could ease the burden of the dietary phe restriction for PKU patients and their families. The time may be right for revisiting the guidelines for follow up of PKU in order to address a number of important issues related to PKU management: promotion of breastfeeding to complementary feeding up to 2 years of age for prevention of early growth retardation and later overweight development, treatment advancements for metabolic control, blood phe and tyr variability, routine screening measures for nutritional biomarkers, neurocognitive and psychological assessments, bone pathology, understanding the challenges of compliance and transitioning into adulthood as an individual with PKU and addressing unmet needs in this population.

Plasma free tryptophan revisited: what you need to know and do before measuring it

Plasma free tryptophan (Trp) is an important peripheral parameter widely used by psychopharmacologists to assess Trp entry into the brain for cerebral serotonin synthesis, although, along with total Trp, it can give much more information on Trp metabolism and disposition. Plasma free Trp is, however, a labile parameter easily influenced by a great many modulators, including fasting, food intake, many prescribed and over the counter medications, consumption of alcoholic and of common hot beverages, illicit drug use, some hormones, exercise and mild stressors. Interpretation of changes in plasma free Trp requires appropriate preparation of ultrafiltrates from freshly isolated plasma or serum, accurate analytical methodology and awareness of the multitude of physiological and pharmacological modulators of its concentration. This article highlights these points and makes recommendations aimed at avoiding pitfalls in studies involving this parameter.

L-Tryptophan: Basic Metabolic Functions, Behavioral Research and Therapeutic Indications

An essential component of the human diet, L-tryptophan is critical in a number of metabolic functions and has been widely used in numerous research and clinical trials. This review provides a brief overview of the role of L-tryptophan in protein synthesis and a number of other metabolic functions. With emphasis on L-tryptophan's role in synthesis of brain serotonin, details are provided on the research uses of L-tryptophan, particularly L-tryptophan depletion, and on clinical trials that have been conducted using L-tryptophan supplementation. The ability to change the rates of serotonin synthesis in the brain by manipulating concentrations of serum tryptophan is the foundation of much research. As the sole precursor of serotonin, experimental research has shown that L-tryptophan's role in brain serotonin synthesis is an important factor involved in mood, behavior, and cognition. Furthermore, clinical trials have provided some initial evidence of L-tryptophan's efficacy for treatment of psychiatric disorders, particularly when used in combination with other therapeutic agents.

Activation of liver tryptophan pyrrolase mediates the decrease in tryptophan availability to the brain after acute alcohol consumption by normal subjects

AIMS

We have previously suggested that acute ethanol consumption by normal subjects decreases the availability of circulating tryptophan (Trp) to the brain by activating liver Trp pyrrolase, the first and rate-limiting enzyme of the (major) kynurenine pathway of Trp degradation. The aim of the present study was to examine this hypothesis further by measuring plasma levels of kynurenine metabolites following alcohol consumption.

METHODS

After an overnight fast and a light breakfast, each of 10 healthy subjects received one of five drinks (placebo and doses of ethanol of 0.2, 0.4, 0.6 and 0.8 g/kg body weight in tonic water) on five different occasions. Blood samples were withdrawn 2 h later and plasma was analysed for concentrations Trp, competing amino acids (CAA) and kynurenine metabolites.

RESULTS

Along with the depletion of plasma Trp and the decrease in its availability to the brain, as expressed by the ratio of [Trp]/[CAA], plasma kynurenine was elevated by doses of ethanol of 0.2-0.8 g/kg body weight. The ratio% of [kynurenine]/[Trp], an index of the expression of Trp pyrrolase activity, was also increased by all doses of ethanol.

CONCLUSIONS

We conclude that activation of liver Trp pyrrolase mediates the depletion of plasma Trp and the decrease in its availability to the brain induced by acute ethanol consumption.

Laser Raman and infrared spectral studies of dl-phenylalaninium nitrate

The vibrational band assignments of dl-phenylalaninium nitrate in the crystalline state are made by recording the infrared and Raman spectra at room temperature. The presence of carbonyl (C=O) group has been identified. The prominent marker bands of the aromatic amino acid phenylalanine have been observed and the various modes of vibration have been assigned. The extensive intermolecular hydrogen bonding in the crystal has been identified by the shifting of bands due to the stretching and bending modes of the various functional groups. The nitrate group forms the anion. The stretching and bending wave numbers of the NO(3)(-) anion are different from those observed for free ion state and the degenerating mode of vibrations is also lifted. These reveal that the crystalline field has influenced the symmetry of the nitrate ion.

Approaches to quantifying protein metabolism in response to nutrient ingestion

The investigation of protein metabolism under various nutritional and physiological conditions has been made possible by the use of indirect, principally tracer-based methods. Most studies were conducted at the whole-body level, mainly using steady-state isotopic techniques and equations based on simple two-pool models, in which amino acids are either free or protein bound. Because whole-body methods disregard regional contributions to protein metabolism, some regional approaches have tried to distinguish the distribution of protein kinetics in the different tissues. The organ-balance tracer technique, involving the arteriovenous catheterization of regions or organs with concomitant isotopic tracer infusion, distinguishes between amino acid uptake and release in the net amino acid balance and measures protein synthesis and degradation under steady-state conditions. Last, the importance has become clear of the difference in dietary and endogenous amino acids recycled from proteolysis for anabolic and catabolic pathways. In humans, the dual tracer technique, which consists of the simultaneous oral/enteral administration and intravenous infusion of different tracers of the same amino acid, allows an estimate of the splanchnic uptake of amino acids administered. Furthermore, the whole-body retention of labeled dietary nitrogen after the ingestion of a single protein meal has enabled a clearer understanding of the metabolic fate of dietary amino acids. Based on such data, a newly developed compartmental model provides a simulation of the regional distribution and metabolism of ingested nitrogen in the fed state by determining its dynamic fate through free and protein-bound amino acids in both the splanchnic and peripheral areas in humans.

Phenylketonuria: tyrosine supplementation in phenylalanine-restricted diets

Treatment of phenylketonuria (PKU) consists of restriction of natural protein and provision of a protein substitute that lacks phenylalanine but is enriched in tyrosine. Large and unexplained differences exist, however, in the tyrosine enrichment of the protein substitutes. Furthermore, some investigators advise providing extra free tyrosine in addition to the tyrosine-enriched protein substitute, especially in the treatment of maternal PKU. In this article, we discuss tyrosine concentrations in blood during low-phenylalanine, tyrosine-enriched diets and the implications of these blood tyrosine concentrations for supplementation with tyrosine. We conclude that the present method of tyrosine supplementation during the day is far from optimal because it does not prevent low blood tyrosine concentrations, especially after an overnight fast, and may result in largely increased blood tyrosine concentrations during the rest of the day. Both high tyrosine enrichment of protein substitutes and extra free tyrosine supplementation may not be as safe as considered at present, especially to the fetus of a woman with PKU. The development of dietary compounds that release tyrosine more slowly could be beneficial. We advocate decreasing the tyrosine content of protein substitutes to approximately 6% by wt (6 g/100 g protein equivalent) at most and not giving extra free tyrosine without knowing the diurnal variations in the blood tyrosine concentration and having biochemical evidence of a tyrosine deficiency. We further advocate that a better daily distribution of the protein substitute be achieved by improving the palatability of these products.

Meal-induced changes in tryptophan:LNAA ratio: effects on craving and binge eating

This study investigated the effects of meals varying in macronutrient composition on plasma tryptophan/large neutral amino acid (tryp:LNAA) ratios and subsequent appetite and mood in women defined as "food cravers." Nine women consumed one of each of a high protein, high carbohydrate and mixed meal on three separate days. Blood samples and appetite and mood ratings were taken before and at intervals up to 150 min after meal consumption. The first subsequent ad libitum food intake was recorded in diaries. The tryp:LNAA ratio increased significantly after the carbohydrate meal compared to protein and mixed meals. No significant correlations between change in tryp:LNAA ratio and mood or macronutrient intake at the ad libitum eating episode were observed. There was a negative correlation between tryp:LNAA ratio and desire to binge eat (p=0.03) and a trend towards a negative correlation between tryp:LNAA ratio and craving for carbohydrate-rich foods (p=0.07). Participants whose ad libitum eating episode was categorized as a binge had a trend (p=0.06) toward lower plasma tryp:LNAA ratio than those who did not binge. Regression analysis showed that the effects of change in tryp:LNAA ratio on desire to binge eat was independent of meal type and changes in insulin and glucose concentrations. These findings suggest that reducing plasma tryp:LNAA ratio, via consumption of a protein-rich meal, may mediate the desire to binge eat in susceptible women.

Measuring protein synthesis by mass isotopomer distribution analysis (MIDA)

The measurement of protein kinetics by isotopic techniques has been hindered by the long-standing difficulty of accurately measuring the isotope content of the biosynthetic precursor pool (aminoacyl-tRNA in tissues). Mass isotopomer distribution analysis (MIDA) is a stable isotope-mass spectrometric (MS) technique for measuring biosynthetic precursor enrichments from measurements on a polymeric product, based on combinatorial probabilities of labeled and unlabeled monomeric subunits. Proteins contain complex isotopomer patterns as a result of their relatively high molecular mass, however, so that resolution of the individual mass isotopomers in the polymeric product (an analytic requirement for MIDA) is technically difficult. An approach for measuring protein synthesis by MIDA is described and tested here: First, in vitro, using a synthetic peptide present in human serum albumin; and then, in vivo, for albumin synthetic rate in rats. A peptide contained in human serum albumin (SVVLLLR) and theoretically recoverable from trypsin/chymotrypsin proteolysis was synthesized by solid-phase peptide synthesis using known mixtures of natural abundance and [5,5, 5-2H3]leucine. Additionally, enriched and natural abundance peptides were mixed in vitro to simulate in vivo biosynthesis and to address problems of instrument accuracy, precision, and data management. The mass isotopomer patterns of the synthetic peptides were analyzed using electrospray ionization (ESI) with both magnetic sector and quadrupole mass analyzers. The resolution of the magnetic sector was superior to that of the quadrupole instrument, but accuracy and precision in the measurement of mass isotopomer abundances and kinetic parameters were comparable and both gave values close to those predicted. Next, rats were infused with [5,5,5-2H3]leucine intravenously, and a leucine-rich peptide was isolated and purified from trypsin-digested rat serum albumin (RHPDYSVSLLLR, 1456 Da) and then analyzed by ESI-MS using a magnetic sector instrument. Precursor pool enrichments and fractional synthetic rates (0.45 +/- 0.03 day-1, t1/2 = 1.53 +/- 0.09 days) were calculated. Biosynthetic rates of rat serum albumin were congruent with previously published values. In summary, measurement of protein synthesis and precursor pool enrichments by MIDA is technically feasible and practical in vivo using proteolytically derived peptides and ESI-MS analysis.

Tyrosine improves cognitive performance and reduces blood pressure in cadets after one week of a combat training course

The effects of the amino acid tyrosine on cognitive task performance were studied on a group of 21 cadets during a demanding military combat training course. In addition, the effects on mood, blood pressure and the norepinephrine metabolite MHPG were determined. Ten subjects received five daily doses of a protein-rich drink containing 2 g tyrosine, and 11 subjects received a carbohydrate rich drink with the same amount of calories (255 kcal). Assessments were made both immediately prior to the combat course and on the 6th day of the course. The group supplied with the tyrosine-rich drink performed better on a memory and a tracking task than the group supplied with the carbohydrate-rich drink. In addition, the supplementation of tyrosine decreased systolic blood pressure. No effects on mood were found. These findings suggest that supplementation with tyrosine may, under operational circumstances characterized by psychosocial and physical stress, reduce the effects of stress and fatigue on cognitive task performance.

Serotonin-immune interactions in detoxified chronic alcoholic patients without apparent liver disease: activation of the inflammatory response system and lower plasma total tryptophan

The aims of the present study were to examine (1) the inflammatory response system (IRS), through measurements of serum interleukin-6 (IL-6), soluble IL-6 receptor (sIL-6R), sgp130 (the soluble form of the IL-6 transducer signal protein), CC16 (Clara Cell protein; an endogenous anti-cytokine), IL-1R antagonist (IL-1RA), IL-8 and sCD14; and (2) the availability of plasma total tryptophan to the brain in chronic alcoholic patients without apparent liver disease (AWLD). Detoxified AWLD patients had significantly lower plasma tryptophan and serum CC16 and significantly higher serum IL-1RA and IL-8 concentrations than normal volunteers. There were significant correlations between the availability of tryptophan to the brain and serum IL-6, IL-8 and IL-1RA (all negative) and CC16 (positive). The results suggest that (1) there is, in detoxified AWLD patients, an activation of the monocytic arm of cell-mediated immunity and a lowered anti-inflammatory capacity of the serum; and that (2) lower availability of plasma tryptophan to the brain in detoxified AWLD patients is related to activation of the IRS. Lower CC16 may be one factor predisposing chronic alcoholic patients toward infectious disorders.

Effect of a protein-rich meal on urinary and salivary free amino acid concentrations in human subjects

The aim of the present study was to investigate whether in healthy volunteers acute changes in plasma free amino acid composition after a protein-rich test meal are reflected in the urinary and salivary concentrations of the corresponding amino acids. The ingestion of a protein-rich meal elicited a significant increase of plasma and urine amino acid concentrations. The postprandial salivary amino acid excretion showed only minor changes. For several amino acids (alanine, arginine, asparagine, glycine, threonine and valine) significant relations were observed between the increase in concentration of these amino acids in venous plasma and urine. In whole saliva, only threonine and valine showed a significant relationship with the corresponding plasma concentration. Our data suggest that the urinary amino acid excretion of several amino acids has the potential for estimating short-term changes in plasma concentrations. Determination of salivary amino acid concentrations seems less appropriate for this purpose.

Time of day and glucose tolerance status affect serum short-chain fatty acid concentrations in humans

Short-chain fatty acids (SCFA) are derived from endogenous (metabolism of fat, carbohydrate, and amino acids) and exogenous (colonic fermentation) sources. To see how time of day and glucose tolerance status influenced serum SCFA concentrations, we determined serum SCFA throughout the day in 22 subjects with impaired glucose tolerance (IGT) and 10 young and eight middle-aged normal controls. On 1 day, insulin sensitivity was assessed as the steady-state plasma glucose (SSPG) level achieved during intravenous infusion of glucose insulin, and somatostatin. On another day, plasma glucose and insulin and serum SCFA levels were measured 12 times over 12 hours with subjects eating a standard diet. SSPG in young controls (5.5 +/- 1.1 mmol/L) was less than in middle-aged controls (9.3 +/- 1.6 mmol/L), which in turn was less than in IGT subjects (13.7 +/- 0.6 mmol/L; P < .01). Mean plasma glucose in IGT subjects was greater than in normal controls, and mean plasma insulin in IGT subjects was higher than in young controls but similar to the levels in middle-aged controls. Mean 12-hour serum acetate in young controls (143 +/- 13 mumol/L) was greater than in middle-aged controls (104 +/- 11 mumol/L) and IGT subjects (113 +/- 5 mumol/L; P < .05). Mean 12-hour serum propionate in young controls (3.8 +/- 0.5 mumol/L) was less than in IGT subjects (5.4 +/- 0.3 mumol/L; P < .01), with middle-aged controls being intermediate (4.6 +/- 0.3 mumol/L). Both young (1.6 +/- 0.3 mumol/L) and middle-aged (1.0 +/- 0.2) controls had lower mean butyrate than IGT subjects (3.1 +/- 0.4 mumol/L; P < .05). Levels of all three SCFA varied significantly during the day, tending to decrease after breakfast and increase transiently after lunch and dinner. It is concluded that both time of day and glucose tolerance status affect serum SCFA levels in nondiabetic humans. The results suggest that serum acetate is derived primarily from colonic fermentation, serum butyrate primarily from endogenous fatty acid metabolism, and serum propionate from both exogenous and endogenous sources.

Plasma amino acid ratios related to brain serotonin synthesis in response to food intake in bulimia nervosa

Fifteen bulimic women (BN) and 19 healthy female controls (CO) were studied. The subjects were cross-over treated with either fluoxetine (FXT) or placebo during 4 days. They received, in randomized order, a breakfast containing pure carbohydrate (CHO) or a protein-rich (PROT) breakfast following day 3 and 4 of each treatment period. Twenty-nine different food items were offered for lunch. The fasting serum glucose and insulin concentrations and the fasting plasma tryptophan (Trp)/large neutral amino acid (LNAA) ratio were slightly higher in BN. The changes of these metabolic parameters in response to a CHO or PROT breakfast were similar in both groups. Across breakfast type, the plasma (Trp)/(LNAA) ratio at 120 min after breakfast was higher in BN. Total caloric intake at lunchtime was less in BN. In CO, less carbohydrate was selected at lunchtime following the CHO breakfast, an effect that was abolished by FXT. Breakfast type or FXT did not have any apparent effect on food intake at lunchtime in BN. This might indicate that bulimic subjects are less sensitive to serotoninergic stimuli than control subjects.

Influences of dietary and intraduodenal lipid on alertness, mood, and sustained concentration

The effects of intraduodenal and dietary lipid on alertness, mood and performance in a task requiring sustained attention were investigated in two studies. The first experiment compared the effect of duodenal infusion of either 100 g/l Intralipid (8.36 kJ/min) or isotonic saline (9 g NaCl/l) in paired studies carried out on two non-consecutive days on five male volunteers. Two consecutive 3 h infusions, one of lipid, the other saline, were given blind on each day using a crossover design. Analysis of variance indicated that lipid significantly reduced alertness (P < 0.05) and affected the speed and accuracy of performance in a sustained attention task (P < 0.05). A second experiment compared the effects on eight male volunteers of two isoenergetic lunches of similar appearance, taste and protein content but differing fat and carbohydrate (CHO) contents (fat energy:CHO, 64:18 v. 7:76). Alertness was lower (P < 0.05) and responses to stimuli in a sustained attention task were slower after the high-fat meal than after the low-fat meal (P < 0.05). In conclusion, infusion of lipid into the small intestine, and the substitution of fat for carbohydrate while keeping energy and protein constant in a lunch, both cause an enhanced postprandial decline in alertness and concentration. This may be related to the presence of lipid in the small intestine.

Efficiency of enteral nitrogen support in surgical patients: small peptides v non-degraded proteins

In a prospective study, 12 intensive care patients, after abdominal surgery, received three alternate six-day courses of two enteral diets with identical nitrogen (0.3 g N/kg per day) and energy (60 kcal/kg per day) supply. The protein hydrolysate (PH) diet contained enzyme-hydrolysed casein and lactoserum (60% small peptides), while the non-degraded protein (NDP) diet contained a nitrogen source of similar amino acid composition, but in the form of non-degraded proteins. The patients were randomised to receive either PH-NDP-PH or NDP-PH-NDP. Parameters reflecting protein metabolism were assessed in the plasma, urine, and stomal effluent on days 1, 6, 12, and 18, three hours after stopping the nutrition (t0), and one hour after restarting it (t1). Comparisons of t1 and t0 values showed that 13 amino acids (including the eight essential amino acids) increased significantly with the protein hydrolysate diet, but only two increased with the non-degraded protein diet. Similarly, with protein hydrolysate, insulin-aemia at t1 was significantly higher than at t0 and correlated with plasma leucine, phenylalanine, alanine, and lysine concentrations. In addition, significant improvements in plasma albumin, transferrin, and retinol binding protein concentrations were seen with protein hydrolysate, together with a significant decrease in the plasma phenylalanine/tyrosine ratio and urinary 3-methylhistidine excretion. We conclude that in patients in intensive care after abdominal surgery enteral support containing small peptides is more effective than an equivalent diet containing whole proteins in restoring plasma amino acid and protein levels.

Tryptophan-morphine interactions and postoperative pain

Patients undergoing abdominal surgery were infused with saline or the 5-hydroxytryptamine (5-HT) precursor tryptophan starting in the operating room and continuing for three hours in the recovery room. There was a nonsignificant trend for patients who received tryptophan to have higher pain scores. In the saline-treated patients, plasma tryptophan was below the range for normal healthy subjects, and there was a strong positive relationship between plasma tryptophan and morphine requirements. These data, taken together with animal data obtained using the formalin pain test, suggest that a 5-HT system in the brain can antagonize the dissociative state produced by morphine, which helps patients to tolerate pain. When plasma tryptophan falls below normal levels, brain 5-HT falls and morphine requirements are reduced. While tryptophan may potentiate spinal 5-HT function to decrease nociceptive afference in some circumstances, there may be clinical conditions in which the use of tryptophan is contraindicated.

The effect of protein or carbohydrate breakfasts on subsequent plasma amino acid levels, satiety and nutrient selection in normal males

Normal subjects were fed protein or carbohydrate breakfasts. Both meals were in the form of a chocolate pudding and had similar sensory qualities. At lunchtime subjects were allowed to select from a buffet. The protein breakfast had a greater satiating power than the carbohydrate breakfast, but there was no difference in overall selection of protein or carbohydrate at lunchtime. However, the carbohydrate breakfast did decrease selection of apple, the only pure carbohydrate food available at lunchtime. In a second experiment changes in plasma amino acid levels were studied after subjects received carbohydrate breakfasts containing 0, 4, 8 or 12% protein, or a danish pastry. Only the 0% protein breakfast increased tryptophan availability to the brain. These experiments were performed to test the hypothesis that alterations in brain 5-hydroxytryptamine, brought about by dietary alterations in brain tryptophan, regulate selection of protein and carbohydrate. The results suggest that this mechanism was not operating in our experiments.

Neutral amino acid plasma levels in healthy subjects: effect of complex carbohydrate consumed along with protein

Six healthy fasting females each received, on different days, 0, 25, or 50 g of complex carbohydrate in the form of white spaghetti containing 11-12% protein along with 200 ml water. Blood was collected before and at intervals for 4 hours after the spaghetti ingestion and assayed for plasma levels of large, neutral amino acids (LNAA), insulin and glucose. The area under the curve for the increase of serum insulin was four times greater after the 50-g dose compared to the 25-g dose of carbohydrate, but the respective areas under the curves for the increases of plasma glucose were identical. The plasma ratio tryptophan/LNAA varied significantly and increased 10% above basal level and 25-30% above control level after either carbohydrate dose, but only the difference for the 50-g dose was significant. Although the main effect for plasma ratio tyrosine/LNAA was also significant, the increases of this ratio above control level were marginal. The main effect for the dose of complex carbohydrate for valine, isoleucine and leucine was significant, and the areas above the curves for the decreases of individual branched-chain amino acids were of the same size after the two doses. Plasma tyrosine, phenylalanine and tryptophan showed no significant variation. The study has shown that consumption of complex carbohydrate along with 11-12% protein (the recommended dietary concentration) slightly increases the plasma ratio tryptophan/LNAA for 4 hours, and that the effect is practically maximal after ingestion of 25 g of the test meal.

Dietary effects on mood and performance

Of 20 young students recruited at a college for nutrition, 10 followed a diet for a period of 3 weeks and 10 were assigned to a control condition. One subject in the control group dropped out. The diet consisted of approximately 70 g protein and 25 g carbohydrate at breakfast and 10 g protein and 100 g carbohydrate at dinner. In between, a protein luncheon was consumed. On the last day of the 3-week period repeated measurements of mood and performance were made, i.e. after breakfast and after dinner. Consequently, the same measurements were made 2 months later to serve as covariates in the analyses to control for base-line differences of the two groups. It was predicted that, in the morning, the performance and the vigour of the diet group would improve whereas, in the evening, performance would become worse and subjects would feel more sleepy. However, the diet group was found to have a higher anger score in the morning (probably due to the unattractive nature of the diet) and a tendency to have a higher fatigue score in the evening compared with the controls. In addition, the diet group performed better in the morning on finger tapping, compared with the control group. With respect to memory scanning, the diet group performed more slowly in the morning in comparison with the control group. From these conflicting results, it was concluded that dietary composition had no effect on mood and behaviour.

Acute effect of protein or carbohydrate breakfasts on human cerebrospinal fluid monoamine precursor and metabolite levels

Patients with normal pressure hydrocephalus who had three lumbar punctures during 1 week ingested either water, a protein breakfast, or a carbohydrate breakfast 2.5 h before each of the lumbar punctures. The CSF was analyzed for biogenic amine precursors and metabolites. The protein meal raised CSF tyrosine levels, a finding consistent with animal data, but did not alter those of tryptophan or any of the biogenic amine metabolites. The carbohydrate meal increased CSF 3-methoxy-4-hydroxyphenylethylene glycol, an unexplained finding. The carbohydrate meal did not affect CSF tryptophan, tyrosine, 5-hydroxyindoleacetic acid, or homovanillic acid. Our results support the idea that in humans protein or carbohydrate meals do not alter plasma amino acid levels sufficiently to cause appreciable changes in CNS tryptophan levels or 5-hydroxytryptamine synthesis.

Macronutrient relationships with meal patterns and mood in the spontaneous feeding behavior of humans

The role of protein, carbohydrate and fat ingestion on self-rated mood and subsequent food intake was investigated using self-reports of spontaneous food intake. Eight male and 30 female undergraduate students were instructed to list everything they ate, when they ate it, and their mood at the time of ingestion. They were asked to make these entries in a diary throughout a nine day period. Mood was rated at the beginning of each meal on three seven point scales; elated-depressed, tired-energetic, and anxious-tranquil. The amount of protein, carbohydrate, and fat as well as the total amount of food energy in each meal and the intermeal intervals (IMIs) prior to and following the meals were calculated with a computerized analysis. The energy content and the amount of each of the macronutrients contained in the stomach at the beginning and end of each meal was estimated with a mathematical model. These data were then intercorrelated using bivariate and multivariate techniques. Momentary self-rated mood was not found to be related to prior macronutrient intake nor was it predictive of subsequent intake. Long term macronutrient intake, averaged over the nine recording days, was found to be related to the averaged mood of the subjects. Although no significant relationships were found between the absolute amounts of the macronutrients ingested and mood, significant correlations were found between the proportion of each macronutrient in the diet and the overall self-rated mood.(ABSTRACT TRUNCATED AT 250 WORDS)

The composition of lunch determines afternoon plasma tryptophan ratios in humans

It is well established that the ratio of the plasma tryptophan concentration to those of the other large neutral amino acids determines the transport of tryptophan into the brain. Brain tryptophan levels, in turn, control production of the neurotransmitter serotonin. Protein-rich meals, when consumed in the morning after an overnight fast, have been shown to decrease the plasma tryptophan ratio, while carbohydrate-rich meals have the opposite effect. We now show that these meals have similar effects when consumed for lunch, even if they are preceded by a small breakfast meal.

Profiling of amino acids in body fluids and tissues by means of liquid chromatography

The needs of urgent diagnoses and the needs emerging from acute forms of diseases have directed progress in amino acid profiling to modern, rapid, automated analyses that can be done at reasonable cost. The first step in this direction was the short programmes of classical ion-exchange chromatography. At the beginning of this review we attempted to survey methods of sample preparation and sample treatment, as these are frequently neglected stages where artefacts or erroneous results may arise. There are basically the following approaches in amino acid profiling by liquid chromatographic techniques. For preliminary screening of a large number of samples in clinical routine planar procedures are the methods of choice, as they allow large numbers of samples to be handled with minimum effort and at very reasonable cost. For more precise profiling, particularly where quantitative data are essential, one can choose between some of the modern procedures for separating underivatized amino acids using modern equipment for cation-exchange chromatography, by making use of a stepped series of lithium citrate buffers with ninhydrin, o-phthalaldehyde or 4-fluoro-7-nitrobenzo-2,1,3-oxadiazole detection. Ninhydrin detection is preferred in those situations where the demands on sensitivity are not high. Where, however, only small amounts of samples are available or high sensitivity is required, one of the latter two methods is preferred. The o-phthalaldehyde procedure is not suitable for the detection of secondary amines and, if these are of interest, then diazole derivatization is to be preferred. At present, however, the ninhydrin and o-phthalaldehyde detection procedures are the most popular. The other choice is to use one of the sophisticated HPLC systems equipped with fluorescence detection and to separate amino acids as derivatives. Here o-phthalaldehyde and 4-fluoro-7-nitrobenzo-2,1,3-oxadiazole derivatives offer the most versatile possibilities. Automation and computerization have penetrated both categories of liquid column separation and are applied to automated sample delivery, automated and computerized gradient formation and quantitation of the data obtained. The tables of metabolic disorders of amino acids and the roles of different amino acids in these disorders should provide preliminary information for clinical chemists.

Breakfast meal composition influences plasma tryptophan to large neutral amino acid ratios of healthy lean young men

The effect of a carbohydrate, a 20% protein, or a carbohydrate +0.3% tryptophan TRP breakfast on plasma large neutral amino acid ratios was studied in 6 healthy men. The carbohydrate-rich meal produced shifts in plasma amino acid concentrations such that plasma TRP/LNAA ratios increased from 0.13 to 0.15 (p less than 0.04) and the protein meal decreased the ratio from 0.14 to 0.11 (p less than 0.04) after 1 hour. Addition of 0.3% TRP to the carbohydrate-rich meal increased plasma TRP/LNAA ratios more than 2-fold. The TRP containing meal was thus the only one likely to influence brain 5-HT synthesis, although the difference between the plasma TRP/LNAA ratios after carbohydrate and protein breakfasts suggests that the brain may distinguish, by synthesizing more or less 5-HT, the composition of breakfast meals.