Mood and cortisol responses following tryptophan-rich hydrolyzed protein and acute stress in healthy subjects with high and low cognitive reactivity to depression

Intestinal tryptophan metabolism in disease prevention and swine production

Tryptophan (Trp) is an essential amino acid that cannot be synthesized by animals. It has been characterized into two different isomers, levorotation-Trp (L-Trp) and dextrorotation-Trp (D-Trp), based on their distinct molecule orientation. Intestinal epithelial cells and gut microbiota are involved in metabolizing L-Trp in the gut via the activation of the kynurenine, serotonin, and indole pathways. However, knowledge regarding D-Trp metabolism in the gut remains unclear. In this review, we briefly update the current understanding of intestinal L/D-Trp metabolism and the function of their metabolites in modulating the gut physiology and diseases. Finally, we summarize the effects of Trp nutrition on swine production at different stages, including growth performance in weaned piglets and growing pigs, as well as the reproduction performance in sows.

Dietary tryptophan-rich protein hydrolysate can acutely impact physiological and psychological measures of mood and stress in healthy adults

BACKGROUND

Tryptophan is the precursor to the mood regulating neurotransmitter serotonin. Its brain bioavailability from food can be dependent on the dietary source. Egg protein hydrolysate (EPH), a dietary supplement rich in tryptophan, has previously shown to acutely impact cognition, mood and stress benefits at 2 g dose. No data exist on the acute effects of lower doses in a food matrix.

METHODS

This exploratory study tested the acute effects of low-doses EPH (0.5, 1 g) in a food matrix on cognition, mood and stress. The study employed a double-blinded randomized controlled parallel design in 45 participants with three arms. The effects of the interventions were measured after a multi-task cognitive stressor on blood biomarkers, self-reported mood states, performances of attention, autonomic parameters and, emotional reactivity responses from electroencephalographic recording.

RESULTS

As compared to the reference, the 1 g EPH dose increased tryptophan bioavailability from baseline, and, both doses improved heart rate variability parameters related to parasympathetic activation while showing differences in the late neural response to negative versus neutral emotions. Post-hoc analyses indicated a gender difference in the baseline tryptophan bioavailability and further examination suggested the change in mood rating depends on the interaction between gender and change from baseline of tryptophan bioavailability.

CONCLUSIONS

Overall, this study suggests that low levels of tryptophan rich EPH in a food matrix positively impact mood or stress in acute settings and adds to the body of evidence linking tryptophan and dietary sources thereof with these benefits. Confirmatory randomized controlled trials are needed to confirm these findings.Trial registration number: CER-VD N°2019-00218.

Stress and Kynurenine-Inflammation Pathway in Major Depressive Disorder

Major depressive disorder (MDD) is one of the most prevalent disorders and causes severe damage to people's quality of life. Lifelong stress is one of the major villains in triggering MDD. Studies have shown that both stress and MDD, especially the more severe conditions of the disorder, are associated with inflammation and neuroinflammation and the relationship to an imbalance in tryptophan metabolism towards the kynurenine pathway (KP) through the enzymes indoleamine-2,3-dioxygenase (IDO), which is mainly stimulated by pro-inflammatory cytokines and tryptophan-2,3-dioxygenase (TDO) which is activated primarily by glucocorticoids. Considering that several pathophysiological mechanisms of MDD underlie or interact with biological processes from KP metabolites, this chapter addresses and discusses the function of these mechanisms. Activities triggered by stress and the hypothalamic-pituitary-adrenal (HPA) axis and immune and inflammatory processes, in addition to epigenetic phenomena and the gut-brain axis (GBA), are addressed. Finally, studies on the function and mechanisms of physical exercise in the KP metabolism and MDD are pointed out and discussed.

Distinct Cecal and Fecal Microbiome Responses to Stress Are Accompanied by Sex- and Diet-Dependent Changes in Behavior and Gut Serotonin

Although diet- and stress-induced perturbations in the microbiome (biotic and abiotic factors) associate with changes in host behavior via the microbiota-gut-brain axis, few mechanisms have been identified. The identification of causative pathways by which the microbiome influences host behavior therefore would benefit from the application of evidence-based conceptual frameworks. One such causal framework is microbial endocrinology which is the study of neuroendocrine axes as avenues of bi-directional neurochemical-based host-microbe crosstalk. As such, we investigated the relationship between diet- and stress-induced alterations in behavior, regional gut serotonergic response, and concomitant changes in the cecal and fecal bacterial populations of male and female mice. Our results demonstrate that sex is a dominant factor in determining compositional changes in the gut microbiome in response to stress and diet modifications. Intestinal serotonergic responses to stress were observed in both sexes but dietary modifications uniquely affected region-specific changes in males and females. Likewise, behavioral alterations diverged between male and female mice. Together, these results demonstrate distinct sex-dependent relationships between cecal and fecal bacterial taxa and behavioral- and serotonergic-responses to stress and diet. The present study demonstrates the importance of including both male and female sexes in the examination of the microbiota-gut-brain axis. As different microbial taxa were identified to associate with the behavioral and gut serotonergic responses of male and female mice, certain bacterial species may hold sex-dependent functional relevance for the host. Future investigations seeking to develop microbiome-based strategies to afford host stress resilience should include sex-based differences in the microbiome.

Changes in kynurenine pathway metabolites after acute psychosocial stress in healthy males: a single-arm pilot study

Chronic stress is associated with an increased conversion of tryptophan (TRP) into kynurenine (KYN). However, only a few studies investigated KYN pathway metabolite concentrations following acute stress in healthy subjects. We hypothesized that TRP/KYN metabolism changes following acute stress, and that KYN pathway metabolites are associated with cortisol and subjective stress responses. In a single-arm pilot study, we explored whether KYN pathway metabolites concentrations were altered after acute stress induced by the Maastricht Acute Stress Test in healthy males (n = 56, mean age: 27 (SD = 4.5) years, BMI: 23 (SD = 1.8) kg/m²). In particular, we examined whether concentrations of TRP decreased, and KYN, kynurenic acid (KYNA), and the ratio of KYN to TRP (KYN:TRP) increased after acute stress. Furthermore, we assessed whether cortisol and subjective stress responses correlated with KYN pathway metabolite measures after stress induction, based on both the area under the curve with respect to the ground (AUCg) as well as the incremental area under the curve (AUCi). Concentrations of TRP, KYN, KYNA, and KYN:TRP were significantly lower after stress induction compared to pre-stress induction (all p < 0.01). AUCi and AUCg reflecting cortisol and subjective stress responses did not correlate with AUCi and AUCg reflecting KYN pathway metabolite responses. These preliminary results indicate that KYN pathway metabolites are lower after acute psychosocial stress induction. Moreover, although chronic stress and subsequent prolonged elevated cortisol concentrations and subjective stress stimulate the conversion of TRP into KYN, acute stress is not associated with such conversion up to 35 minutes after stress induction.

Stressed out and fed up: The effect of stress on maternal feeding behaviors and the moderating role of executive function

Stress is associated with a range of unhealthy eating habits, yet few studies have examined how stress may influence the intergenerational transmission of eating habits from parents to their children. Specifically, there is a lack of data regarding the role of stress on feeding practices. Moreover, most work investigating the associations between parental stress and their feeding behaviors has been correlational, limiting our understanding of causality. In the current study, we used an experimental design, induced high and low stress in mothers using a standard laboratory stressor, and observed mother-child interactions during a snack break. We also examined the potential role of maternal executive functioning (EF) for buffering the effects of stress on maternal feeding behaviors. Levels of maternal stress were manipulated with the Trier Social Stress Task (TSST) in a community sample (N = 80 dyads, Child M_age = 41.89 months, female = 43). We measured maternal EF with a series of computerized tasks. Maternal feeding behaviors were coded for controlling behaviors, which included pressuring and restricting behaviors. Results indicate a main effect of stress on controlling feeding behaviors, such that mothers in the high-stress condition exhibited higher levels of controlling behaviors. The effect of stress on controlling feeding behaviors was ameliorated among mothers with higher levels of EF after controlling for child age and income. Results provide causal evidence for the role of stress on feeding behaviors and suggest EF as a factor to be considered in the treatment and prevention of diet-related illnesses.

Egg intake moderates the rate of memory decline in healthy older adults

Eggs contain important compounds related to enhanced cognition, but it is not clear if egg consumption, as a whole, has a direct impact on memory decline in older adults. This study aimed to determine whether egg intake levels predict the rate of memory decline in healthy older adults after sociodemographic and dietary controls. We conducted a secondary analysis of data from 470 participants, age 50 and over, from the Biospsychosocial Religion and Health Study. Participants completed a food frequency questionnaire, which was used to calculate egg intake and divide participants into Low (<23 g/week, about half an egg), Intermediate (24-63 g/week, half to 1½ eggs) and High (≥63 g/week, about two or more eggs) tertiles. Participants were administered the California Verbal Learning Test - 2nd Edition (CVLT-II) Short Form in 2006-2007, and 294 of them were again tested in 2010-2011. Using linear mixed model analysis, no significant cross-sectional differences were observed in CVLT-II performance between egg intake levels after controlling for age, sex, race, education, body mass index, cardiovascular risk, depression and intake of meat, fish, dairy and fruits/vegetables. Longitudinally, the Intermediate egg group exhibited significantly slower rates of decline on the CVLT-II compared to the Low egg group. The High egg group also exhibited slower rates of decline, but not statistically significant. Thus, limited consumption of eggs (about 1 egg/week) was associated with slower memory decline in late life compared to consuming little to no eggs, but a dose-response effect was not clearly evident. This study may help explain discrepancies in previous research that did not control for other dietary intakes and risk factors.

The Influence of Social Support and Ability Perception on Coping Strategies for Competitive Stress in Soccer Players: The Mediating Role of Cognitive Assessment

Objectives: To explore the effect of social support and ability perception on stress coping strategies for competitive stress, and to reveal the mediating effects of primary and secondary evaluation, so as to further improve the theoretical model of stress coping in soccer players.

Methods: A total of 331 male athletes from 22 teams in the Chengdu Middle School Campus Football League were taken as survey samples, and surveys were conducted on their stress experience, social support, ability perception, cognitive assessment, and coping strategies for competition stress. SPSS 21.0 and AMOS 21.0 statistical analysis software were used. Descriptive statistics, correlation analysis, exploratory factor analysis (EFA), and confirmatory factor analysis (CFA) were used to process the obtained data.

Results: (1) Positive primary assessment acted as a full mediator in the relationship between social support and secondary assessments, and negative primary assessment acted as a partial mediator in the relationship between competence perception and secondary assessments; (2) Secondary assessment played a partial mediating role between positive primary assessment and positive coping strategies, and a full mediating role between negative primary assessment and positive coping strategies; (3) Secondary assessments played the mediator neither between social support and a coping strategy for stress nor competence perception and a coping strategy for stress; (4) Positive primary assessment, positive negative assessment, and secondary assessment all had significant positive benefits for positive coping. Still, the impact of positive primary assessment on positive coping was significantly better than negative primary assessment and secondary assessment.

Conclusion: The coping strategy for the competitive stress model proposed by this study has a very good fit for the causal model. It can be used to explain the observed data from soccer players in middle schools. The primary and secondary assessments play different roles in the model. The combination of problem focuses and emotional focus on the positive stress coping strategy is suitable in the field of competitive sports. Still, the relevant research results need to be further explored and verified in the future.

Decrease in Salivary Serotonin in Response to Probiotic Supplementation With Saccharomyces boulardii in Healthy Volunteers Under Psychological Stress: Secondary Analysis of a Randomized, Double-Blind, Placebo-Controlled Trial

BACKGROUND

Bacterial probiotics are thought to exert a serotonergic effect relevant to their potential antidepressant and pro-cognitive action, but yeast probiotics have not been tested. The aim of the present study was to determine whether 30-day supplementation with Saccharomyces boulardii affects the level of salivary serotonin under psychological stress and identify the factors associated with it.

METHODS

Healthy medical students were randomized to ingest Saccharomyces boulardii CNCM I-1079 or placebo before a stressful event. Salivary serotonin concentration was assessed before and at the end of supplementation. Moreover, obtained results were compared to psychological, biochemical, physiological and sociodemographic study participants data.

RESULTS

Data of thirty-two participants (22.8 ± 1.7 years of age, 16 males) was available for the main analysis. Supplementation with Saccharomyces boulardii decreased salivary serotonin concentration under psychological stress by 3.13 (95% CI 0.20 to 6.07) ng/mL, p = 0.037, as compared to placebo. Salivary serotonin was positively correlated with salivary metanephrine (β = 0.27, 95% CI 0.02 to 0.52, p = 0.031) and pulse rate (β = 0.28, 95% CI 0.05 to 0.50, p = 0.018), but insignificantly with anxiety, depression, eating attitudes and information retrieval.

CONCLUSIONS

Saccharomyces boulardii CNCM I-1079 may be distinct from bacterial probiotics in its salivary serotonergic effect, which appears positively linked to symapathoadrenal markers. The study requires cautious interpretation, and further investigation.

Characterization of the Metabolic, Clinical and Neuropsychological Phenotype of Female Carriers of the Premutation in the X-Linked FMR1 Gene

The X-linked FMR1 premutation (PM) is characterized by a 55-200 CGG triplet expansion in the 5'-untranslated region (UTR). Carriers of the PM were originally thought to be asymptomatic; however, they may present general neuropsychiatric manifestations including learning disabilities, depression and anxiety, among others. With age, both sexes may also develop the neurodegenerative disease fragile X-associated tremor/ataxia syndrome (FXTAS). Among carriers, females are at higher risk for developing immune disorders, hypertension, seizures, endocrine disorders and chronic pain, among others. Some female carriers younger than 40 years old may develop fragile X-associated primary ovarian insufficiency (FXPOI). To date, no studies have addressed the metabolic footprint - that includes mitochondrial metabolism - of female carriers and its link to clinical/cognitive manifestations. To this end, we performed a comprehensive biochemical assessment of 42 female carriers (24-70 years old) compared to sex-matched non-carriers. By applying a multivariable correlation matrix, a generalized bioenergetics impairment was correlated with diagnoses of the PM, FXTAS and its severity, FXPOI and anxiety. Intellectual deficits were strongly correlated with both mitochondrial dysfunction and with CGG repeat length. A combined multi-omics approach identified a down-regulation of RNA and mRNA metabolism, translation, carbon and protein metabolism, unfolded protein response, and up-regulation of glycolysis and antioxidant response. The suboptimal activation of the unfolded protein response (UPR) and endoplasmic-reticulum-associated protein degradation (ERAD) response challenges and further compromises the PM genetic background to withstand other, more severe forms of stress. Mechanistically, some of the deficits were linked to an altered protein expression due to decreased protein translation, but others seemed secondary to oxidative stress originated from the accumulation of either toxic mRNA or RAN-derived protein products or as a result of a direct toxicity of accumulated metabolites from deficiencies in critical enzymes.

A systematic review of the effect of L-tryptophan supplementation on mood and emotional functioning

L-tryptophan (TRP), one of the essential amino acids in humans, is a precursor of serotonin, and hence its intake is closely related to the suppression of depressed and anxious moods. We did a systematic review of RCTs to examine the effects of tryptophan intake on the mood of healthy adults by searching PubMed, the Cochrane Library, and Ichu-shi according to PRISMA guidelines. As a result, 11 RCTs met the criteria and were accepted. Four RCTs showed the effects of tryptophan intake on negative feelings and happy feelings in healthy individuals, with significant differences between the treatment and the control groups. This suggests that TRP intake may be an effective approach to decrease anxiety and increase positive mood in healthy individuals. On the other hand, the effectiveness of TRP for aggressive feelings was not recognized. Reviewing these 11 RCTs, we concluded that taking 0.14-3 g of TRP per day in addition to the usual meal can be expected to improve the mood of healthy individuals. In order to estimate the optimum amount of TRP intake more accurately, further studies need to be conducted with more appropriate settings of intake period, intake frequency, and intake method.

Increasing Dietary Carbohydrate as Part of a Healthy Whole Food Diet Intervention Dampens Eight Week Changes in Salivary Cortisol and Cortisol Responsiveness

It is largely unknown whether and how whole food diets influence psychological stress and stress system responsiveness. To better understand the effects of whole diets on stress system responsiveness, we examined randomized control trial effects of a whole food diet based on the Dietary Guidelines for Americans (DGA) on cortisol responsiveness. A randomized, double-blind, controlled 8-week intervention was conducted in overweight and obese women to examine differentiated effects between two diet intervention groups: one based on the 2010 DGA and the other one based on a typical American diet (TAD). During a test week that occurred at baseline and again after 8 weeks of the intervention, we assessed salivary cortisol collected at 14 selected times across the day, including upon awakening, at bedtime, and during a test visit, and administered a standardized social stress task (Trier Social Stress Test, TSST). There were no statistical differences between the diet groups in salivary cortisol at baseline or after 8 weeks. However, when considering differences in dietary carbohydrate, but not fat or protein, from the pre-intervention (habitual) to the intervention period, there was a significant (P = 0.0001) interaction between diet group, intervention week, saliva sample, and level of intervention-based change in carbohydrate consumption. This interaction was reflected primarily by an 8-week reduction in salivary cortisol during a period just prior to (log Δ −0.35 ± 0.12 nmol/L) and 30 (log Δ −0.49 ± 0.12 nmol/L), 60 (log Δ −0.50 ± 0.13 nmol/L), 90 (log Δ −0.51 ± 0.13 nmol/L), and 120 (log Δ −0.4476 ± 0.1231 nmol/L) min after the TSST in the DGA group having the highest increase (90th percentile) in carbohydrate consumption. In support of this finding, we also found significant (P < 0.05) and inverse linear associations between dietary carbohydrate and log salivary cortisol, with the strongest negative association (β: −0.004 ± 0.0015, P = 0.009) occurring at 30 min post-TSST, but only in the DGA group and at week 9 of the intervention. Together, increasing dietary carbohydrate as part of a DGA-based diet may reduce circulating cortisol and dampen psychological stress-related cortisol responsiveness.

Does aerobic exercise associated with tryptophan supplementation attenuates hyperalgesia and inflammation in female rats with experimental fibromyalgia?

The objective of this study was to verify the effects of aerobic exercise associated with tryptophan (TRP) supplementation on hyperalgesia, as well as on cortisol, IL-6 and TNF concentrations in female rats with experimental fibromyalgia (FM). Female Wistar rats (initial body weight: ~ 350 g; age: 12 months) were randomly divided into 5 groups: CON (Control); F (Fibromyalgia induced); FE (Fibromyalgia induced plus exercise); FES (Fibromyalgia induced plus exercise and TRP supplementation) and FS (Fibromyalgia induced plus TRP supplementation). Fibromyalgia was induced with two injections (20 μL) of acidic saline (pH 4.0) into the right gastrocnemius muscle with a 3-day interval. Control animals received the same doses of neutral saline (pH 7.4). The exercised animals underwent progressive low-intensity aerobic exercise (LIAE) on a treadmill (10–12 m/min, 30–45 min/day, 5 days/week) for three weeks. During this period, the supplemented animals received a TRP supplemented diet (210 g/week), while the others received a control diet. Mechanical hyperalgesia was evaluated weekly and serum cortisol and muscle IL-6 and TNF concentrations were assessed after three weeks of interventions. Experimental FM caused bilateral hind paw hyperalgesia and augmented serum cortisol and muscle IL-6 concentrations. After 3 weeks of interventions, LIAE alone reduced hyperalgesia (151%) and reduced serum cortisol concentrations (72%). Tryptophan supplementation itself diminished hyperalgesia (57%) and reduced serum cortisol concentrations (67%). Adding TRP supplementation to LIAE did not further reduce hyperalgesia significantly (11%), which was followed by an important decrease in muscle IL-6 concentrations (68%), though reduction in serum cortisol pulled back to 45%. Muscle TNF concentrations were not affected. In conclusion, the association of TRP supplementation to LIAE does not potentiate significantly the reduction of bilateral mechanical hyperalgesia promoted by LIAE in female rats with experimental FM, however an important decrease in IL-6 is evident.

Tryptophan Metabolic Pathways and Brain Serotonergic Activity: A Comparative Review

The essential amino acid L-tryptophan (Trp) is the precursor of the monoaminergic neurotransmitter serotonin (5-hydroxytryptamine, 5-HT). Numerous studies have shown that elevated dietary Trp has a suppressive effect on aggressive behavior and post-stress plasma cortisol concentrations in vertebrates, including teleosts. These effects are believed to be mediated by the brain serotonergic system, even though all mechanisms involved are not well understood. The rate of 5-HT biosynthesis is limited by Trp availability, but only in neurons of the hindbrain raphe area predominantly expressing the isoform TPH2 of the enzyme tryptophan hydroxylase (TPH). In the periphery as well as in brain areas expressing TPH1, 5-HT synthesis is probably not restricted by Trp availability. Moreover, there are factors affecting Trp influx to the brain. Among those are acute stress, which, in contrast to long-term stress, may result in an increase in brain Trp availability. The mechanisms behind this stress induced increase in brain Trp concentration are not fully understood but sympathetic activation is likely to play an important role. Studies in mammals show that only a minor fraction of Trp is utilized for 5-HT synthesis whereas a larger fraction of the Trp pool enters the kynurenic pathway. The first stage of this pathway is catalyzed by the hepatic enzyme tryptophan 2,3-dioxygenase (TDO) and the extrahepatic enzyme indoleamine 2,3-dioxygenase (IDO), enzymes that are induced by glucocorticoids and pro-inflammatory cytokines, respectively. Thus, chronic stress and infections can shunt available Trp toward the kynurenic pathway and thereby lower 5-HT synthesis. In accordance with this, dietary fatty acids affecting the pro-inflammatory cytokines has been suggested to affect metabolic fate of Trp. While TDO seems to be conserved by evolution in the vertebrate linage, earlier studies suggested that IDO was only present mammals. However, recent phylogenic studies show that IDO paralogues are present within the whole vertebrate linage, however, their involvement in the immune and stress reaction in teleost fishes remains to be investigated. In this review we summarize the results from previous studies on the effects of dietary Trp supplementation on behavior and neuroendocrinology, focusing on possible mechanisms involved in mediating these effects.

The association of omega-3 fatty acid levels with personality and cognitive reactivity

OBJECTIVE

Low omega (n)-3 polyunsaturated fatty acid (PUFA) levels have been found in patients with various major psychiatric disorders. This study aims to identify whether psychological vulnerabilities (personality and cognitive reactivity) underlying these psychiatric conditions are also associated with n-3 PUFA blood levels.

METHODS

Data was used from 2912 subjects (mean age 41.9 years, 66.4% female) from the Netherlands Study of Depression and Anxiety (NESDA). Five personality dimensions (NEO Five Factor Inventory) and cognitive reactivity measures (Leiden Index of Depression Sensitivity-Revised and Anxiety Sensitivity Index) were assessed. Plasma n-3 PUFA and docosahexaenoic acid (DHA) levels (as ratios against total fatty acids; mmol%) were assessed using a nuclear magnetic resonance platform.

RESULTS

Low n-3 PUFA and DHA levels were associated with high neuroticism (Standardized beta (Beta) = -0.045, 95% Confidence Interval (CI) = -0.079 to -0.010, p = 0.011; Beta = -0.058, 95%CI = -0.093 to -0.022, p = 0.001), low extraversion (Beta = 0.065, 95%CI = 0.031 to 0.099, p < 0.001; Beta = 0.074, 95%CI = 0.039 to 0.109, p < 0.001) and low conscientiousness (Beta = 0.060, 95%CI = 0.027 to 0.093, p < 0.001; Beta = 0.074, 95%CI = 0.039 to 0.108, p < 0.001). Low n-3 PUFA and DHA levels were related to high hopelessness/suicidality (Beta = -0.059, 95%CI = -0.096 to -0.023, p = 0.001; Beta = -0.078, 95%CI = -0.116 to -0.041, p < 0.001), but not with other cognitive reactivity measures. Directions of associations were generally consistent in subjects with and without a current depressive disorder.

CONCLUSION

Low n-3 PUFA and DHA levels are associated with personality (high neuroticism, low extraversion and low conscientiousness) and cognitive reactivity (high hopelessness/suicidality). Effect sizes were rather small, but in line with previous research on personality and chronic diseases. Future research should examine which lifestyle and/or biological pathways underlie these associations.

Association between habitual tryptophan intake and depressive symptoms in young and middle-aged women

BACKGROUND

The intake of tryptophan, the precursor of serotonin, is assumed to affect serotonin availability and depression onset. Nevertheless, a definitive relationship between dietary tryptophan intake and depressive symptoms has not been established. We examined the association between tryptophan intake and depressive symptoms screened in a group of 4272 first-year female dietetic students and 3651 their mothers.

METHODS

Dietary tryptophan intake during the preceding month was assessed with a validated, self-administered diet history questionnaire. Depressive symptoms were assessed with the Center for Epidemiologic Studies Depression Scale (CES-D) using two cutoff scores: CES-D score ≥ 16 and CES-D score ≥ 19 (the optimal cutoff score for Japanese people). The multivariate adjusted prevalence ratio (PR) and 95% confidence interval (CI) for depressive symptoms were calculated using Poisson regression analysis.

RESULTS

The prevalence of depressive symptoms (CES-D score ≥ 16) was 50.0% for young women and 26.5% for middle-aged women. The adjusted PR (95% CI) for depressive symptoms in the highest versus lowest quintile of tryptophan intake was 0.84 (0.75, 0.93) in young women (P for trend < 0.0001) and 0.83 (0.64, 1.01) in middle-aged women (P for trend < 0.0001). These associations were stable even when depressive symptoms were defined as a CES-D score ≥ 19.

LIMITATIONS

This is a cross-sectional study. Depressive symptoms were assessed using a self-reported questionnaire.

CONCLUSIONS

This cross-sectional study showed that a higher tryptophan intake was independently associated with a lower prevalence of depressive symptoms in young Japanese women.

Is There a Relationship between Vegetarianism and Seasonal Affective Disorder? A Pilot Study

BACKGROUND AND AIM

Seasonal patterns of food intake are found in healthy individuals and particularly in patients with seasonal affective disorder (SAD). One nutritional choice is a vegetarian diet.

METHODS

In a Finnish population study, FINRISK 2012, information about diet and SAD was collected. In a Dutch outpatient clinic, SAD patients were asked if they were vegetarian.

RESULTS

The percentage of SAD patients among Finnish vegetarians was 4 times higher than in the normal population. The percentage of vegetarians among the SAD patients in a Dutch outpatient clinic was 3 times higher than in the normal population. In the Dutch population, the seasonal loss of energy, in particular, is related to vegetarianism.

CONCLUSION

These findings suggest a possible link between vegetarianism and SAD.

Intake of tryptophan-enriched whey protein acutely enhances recall of positive loaded words in patients with multiple sclerosis

BACKGROUND & AIMS

Multiple sclerosis (MS) has physiological and/or immunological characteristics that diminish serotonin metabolism, a neurotransmitter associated with affective and cognitive functions. The aim was examine the acute and dose-dependent effects of a dietary tryptophan (TRP) enrichment on affective and cognitive functions in MS patients. We hypothesized that increased dietary availability of the amino acid TRP enhances serotonin concentrations and improves neuropsychological functions.

METHODS

In a double-blind, placebo-controlled, crossover study, MS patients with (n = 15) and without (n = 17) depressed mood ingested a whey protein mixture with 4 different amounts of TRP. Mood states, total plasma TRP and plasma TRP/ΣLNAA ratio were measured during each test session and cognitive tasks were conducted three hours after dietary intake.

RESULTS

A fast, transient and dose-dependent increase of total plasma TRP and TRP/ΣLNAA ratio was found. Ratings of negative mood decreased over time, independent of the TRP dose. Relative to whey-only, immediate word recall and delayed recognition improved after ingestion of the lowest added TRP dose and was mainly due to better recollection for positive loaded words. Executive functions were not affected by a difference in TRP availability.

CONCLUSIONS

A moderate addition of TRP to whey protein enhances memory processes without improving the mood state in MS. ccmo-registration number is NL32316.096.10.

Milk proteins as a source of tryptophan-containing bioactive peptides

Tryptophan (W) is an essential amino acid which is primarily required for protein synthesis. It also acts as a precursor of key biomolecules for human health (serotonin, melatonin, tryptamine, niacin, nicotinamide adenine dinucleotide (NAD), phosphorylated NAD (NADP), quinolinic acid, kynureric acid, etc.). Among dietary proteins, milk proteins are particularly rich in W. W residues within milk proteins may be released by proteolytic/peptidolytic enzymes either as a free amino acid or as part of peptide sequences. Different W-containing peptides originating from milk proteins have been shown in vitro to display a wide range of bioactivities such as angiotensin converting enzyme (ACE) inhibition along with antioxidant, antidiabetic and satiating related properties. Free W has been shown in certain instances to have an effect on cognition and the aforementioned bioactive properties. However, a higher bioactive potency has generally been observed with specific W-containing peptides compared to free W. Since W is thermolabile, the impact of processing on the stability of W-containing peptides needs to be considered. Milk protein-derived W-containing peptides may have significant potential as natural health promoting agents in humans.

How are neuroticism and depression related to the psychophysiological stress response to acute stress in healthy older people?

Neuroticism and depressive symptomatology have been related to a heightened and diminished physiological stress response, which may partly explain their negative relationship with health and wellbeing. Identifying factors that may increase disease vulnerability is especially relevant in older people, whose physiological systems decline. With this in mind, we investigated the influence of neuroticism and depression on the psychophysiological stress response in healthy older people (from 55 to 76years old). A total of 36 volunteers were exposed to a stressful task (Trier Social Stress Test, TSST), while 35 volunteers performed a control non-stressful task. The physiological stress response was assessed through measures of cortisol, alpha-amylase, heart rate (HR). Our results showed that, neuroticism was not related to physiological stress response. However, depression was related to higher cortisol response and lower HR reactivity in the stress condition. In summary, emotional states such as depressive mood seem to amplify the cortisol stress response and reduce the cardiovascular response, whereas more stable dispositions such as neuroticism did not affect stress response in older people. These findings confirm, in healthy older people, the adverse effects of depression, acting on different subsystems of the stress response.

A randomized controlled trial to test the effect of multispecies probiotics on cognitive reactivity to sad mood

BACKGROUND

Recent insights into the role of the human microbiota in cognitive and affective functioning have led to the hypothesis that probiotic supplementation may act as an adjuvant strategy to ameliorate or prevent depression.

OBJECTIVE

Heightened cognitive reactivity to normal, transient changes in sad mood is an established marker of vulnerability to depression and is considered an important target for interventions. The present study aimed to test if a multispecies probiotic containing Bifidobacterium bifidum W23, Bifidobacterium lactis W52, Lactobacillus acidophilus W37, Lactobacillus brevis W63, Lactobacillus casei W56, Lactobacillus salivarius W24, and Lactococcus lactis (W19 and W58) may reduce cognitive reactivity in non-depressed individuals.

DESIGN

In a triple-blind, placebo-controlled, randomized, pre- and post-intervention assessment design, 20 healthy participants without current mood disorder received a 4-week probiotic food-supplement intervention with the multispecies probiotics, while 20 control participants received an inert placebo for the same period. In the pre- and post-intervention assessment, cognitive reactivity to sad mood was assessed using the revised Leiden index of depression sensitivity scale.

RESULTS

Compared to participants who received the placebo intervention, participants who received the 4-week multispecies probiotics intervention showed a significantly reduced overall cognitive reactivity to sad mood, which was largely accounted for by reduced rumination and aggressive thoughts.

CONCLUSION

These results provide the first evidence that the intake of probiotics may help reduce negative thoughts associated with sad mood. Probiotics supplementation warrants further research as a potential preventive strategy for depression.

Chronic treatment with a tryptophan-rich protein hydrolysate improves emotional processing, mental energy levels and reaction time in middle-aged women

Common pharmacological treatments of mood disorders aim to modulate serotonergic neurotransmission and enhance serotonin levels in the brain. Brain serotonin levels are dependent on the availability of its food-derived precursor essential amino acid tryptophan (Trp). We tested the hypothesis that delivery of Trp via food may serve as an alternative treatment, and examined the effects of a Trp-rich, bioavailable dietary supplement from egg protein hydrolysate on cognitive and emotional functions, mood state, and sleep quality. In a randomised, placebo-controlled, parallel trial, fifty-nine mentally and physically healthy women aged 45-65 years received placebo (n 30) or the supplement (n 29) (both as 0.5 g twice per d) for 19 d. Emotional processing was significantly changed by supplementation, exhibiting a shift in bias away from negative stimuli. The results for the Affective Go/No-Go Task exhibited a slowing of responses to negative words, suggesting reduced attention to negative emotional stimuli. The results for the Facial Emotional Expression Rating Task also supported a shift away from attention to negative emotions and a bias towards happiness. An increase in arousal-like symptoms, labelled 'high energy', shorter reaction times and a slight benefit to sustained attention were observed in the treated subjects. Finally, when the supplement was taken 60-90 min before bedtime, a feeling of happiness before going to bed was consistently reported. In summary, daily consumption of a low-dose supplement containing bioavailable Trp may have beneficial effects on emotional and cognitive functions.

Disorder-specific cognitive profiles in major depressive disorder and generalized anxiety disorder

BACKGROUND

This investigation examines differences in cognitive profiles in subjects with major depressive disorder (MDD) and generalized anxiety disorder (GAD).

METHODS

Data were used from subjects with current MDD (n = 655), GAD (n = 107) and comorbid MDD/GAD (n = 266) diagnosis from the Netherlands Study of Depression and Anxiety (NESDA). The Composite Interview Diagnostic Instrument was used to diagnose MDD and GAD. Cognitive profiles were measured using the Leiden Index of Depression Sensitivity, the Anxiety Sensitivity Index, and the Penn State Worry Questionnaire.

RESULTS

Results showed that differences in cognitive profiles between single MDD and single GAD subjects were present: scores on hopelessness/suicidality and rumination were significantly higher in MDD than GAD, whereas anxiety sensitivity for physical concerns and pathological worry were higher in GAD than MDD. The cognitive profile of comorbid MDD/GAD showed more extreme depression cognitions compared to single disorders, and a similar anxiety profile compared to single GAD subjects.

CONCLUSIONS

Despite the commonalities in cognitive profiles in MDD and GAD, there are differences suggesting that MDD and GAD have disorder-specific cognitive profiles. Findings of this investigation give support for models like the cognitive content-specificity model and the tripartite model and could provide useful handles for treatment focus.

Association between mood and diet quality in subjects with metabolic syndrome participating in a behavioural weight-loss programme: a cross-sectional assessment

BACKGROUND/OBJECTIVE

The interplay between individual's mood fluctuations and nutrition has important health implications. However, little information is available on the relationship between dietary intake and mood state in a population with metabolic syndrome (MetS). The aim of the present study was to evaluate the association between dietary intake and mood state in subjects with MetS.

METHODS

This cross-sectional study was based on the baseline data of 84 volunteers (mean age 49 ± 1 years) recruited into the Metabolic Syndrome Reduction in Navarra-Spain (RESMENA-S) study. Mood state was determined using a mood thermometer visual analogue scale. The dietary intake was assessed with a 48-hours weighted food record, from which a Healthy Eating Index (HEI) score was obtained. Anthropometrical measurements and biochemical parameters were also analysed.

RESULTS

At baseline, a positive association between mood thermometer and HEI was observed. Among the 10 HEI components, vegetables, fruits, calories from lipids, saturated fatty acids, and dietary variety were related with higher mood. Moreover, those participants who consumed more water, fibre, vitamin B6, ascorbic acid, tryptophan, magnesium, and selenium have higher mood.

DISCUSSION

In conclusion, an association between both the overall dietary pattern and isolated nutrients with mood state was observed. The analyses of both dietary patterns and specific nutrients are important to determine the association between mental disorders and dietary intake.

Effects of daily intake of yoghurt enriched with bioactive components on chronic stress responses: a double-blinded randomized controlled trial

Chronic stress has a negative influence on health. The aim was to determine stress reducing effects of yoghurt enriched with bioactive components as compared to normal yoghurt. High-trait anxiety individuals (n = 67) aged 18-63 years participated in a randomized, placebo-controlled, double-blinded intervention with parallel groups. They received either yoghurt enriched with alpha-lactalbumin, casein tripeptides and B vitamins (active) or isoenergetic standard yoghurt (control). To detect changes in psychological and physiological stress, State-Trait Anxiety Inventory, Profile of Mood States, salivary cortisol, inflammatory markers, blood pressure, heart rate variability (HRV) and actigraphy were monitored. We observed higher ratings of vigor (p = 0.047) and reduced feeling of inefficiency (p = 0.048) in the active group. HRV (baseline adjusted mean 49.1 ± 2.3 ms) and recovery index (106.6 ± 33.4) were higher in the active group than in controls (42.5 ± 2.2 ms and 80.0 ± 29.3) (p = 0.046 and p = 0.02, respectively). In conclusion, daily intake of yoghurt enriched with bioactive components may aid in stress coping.

Effects of acute treatment with a tryptophan-rich protein hydrolysate on plasma amino acids, mood and emotional functioning in older women

RATIONALE

Effective functioning of the neurotransmitter serotonin is important for optimal cognitive and emotional function. Dietary supplements able to increase availability to the brain of the precursor amino acid, tryptophan (TRP), and thereby enhance serotonin synthesis, can have measurable impact on these psychological processes.

OBJECTIVES

This study involves a randomised controlled trial of a TRP-rich egg-white protein hydrolysate (DSM Nutritional Products Ltd., Switzerland) on plasma amino acids, cognition, mood and emotional processing in older women.

METHODS

Following a baseline test day without treatment, 60 healthy women aged 45-65 years received drinks containing either 2 or 4 g of TRP-rich protein hydrolysate product or 3.11 g casein hydrolysate as a control. One hour later, they undertook a 2-h battery of cognitive and emotional tests.

RESULTS

The TRP-rich protein hydrolysate produced the expected dose-dependent increase in the ratio of plasma TRP to competing large neutral amino acids. TRP-rich protein hydrolysate (2 g only) prevented both the decline in wellbeing and increase in fatigue seen over the test session in the control group. This treatment dose resulted in a significant shift in emotional processing towards positive words and reduced negative bias in assessing negative facial expressions. Effects on cognition were small and not statistically reliable and are not reported here. However, there was no evidence for any adverse effects.

CONCLUSIONS

Consumption of a low dose of TRP-rich protein hydrolysate may have beneficial effects on emotional function that could promote feelings of wellbeing, possibly conferring resistance to deterioration in mood in healthy subjects or depressive episodes.

Biological and psychological markers of stress in humans: focus on the Trier Social Stress Test

Validated biological and psychological markers of acute stress in humans are an important tool in translational research. The Trier Social Stress Test (TSST), involving public interview and mental arithmetic performance, is among the most popular methods of inducing acute stress in experimental settings, and reliably increases hypothalamic-pituitary-adrenal axis activation. However, although much research has focused on HPA axis activity, the TSST also affects the sympathetic-adrenal-medullary system, the immune system, cardiovascular outputs, gastric function and cognition. We critically assess the utility of different biological and psychological markers, with guidance for future research, and discuss factors which can moderate TSST effects. We outline the effects of the TSST in stress-related disorders, and if these responses can be abrogated by pharmacological and psychological treatments. Modified TSST protocols are discussed, and the TSST is compared to alternative methods of inducing acute stress. Our analysis suggests that multiple readouts are necessary to derive maximum information; this strategy will enhance our understanding of the psychobiology of stress and provide the means to assess novel therapeutic agents.

Chrononutrition against oxidative stress in aging

Free radicals and oxidative stress have been recognized as important factors in the biology of aging and in many age-associated degenerative diseases. Antioxidant systems deteriorate during aging. It is, thus, considered that one way to reduce the rate of aging and the risk of chronic disease is to avoid the formation of free radicals and reduce oxidative stress by strengthening antioxidant defences. Phytochemicals present in fruits, vegetables, grains, and other foodstuffs have been linked to reducing the risk of major oxidative stress-induced diseases. Some dietary components of foods possess biological activities which influence circadian rhythms in humans. Chrononutrition studies have shown that not only the content of food, but also the time of ingestion contributes to the natural functioning of the circadian system. Dietary interventions with antioxidant-enriched foods taking into account the principles of chrononutrition are of particular interest for the elderly since they may help amplify the already powerful benefits of phytochemicals as natural instruments with which to prevent or delay the onset of common age-related diseases.

Breakfast high in whey protein or carbohydrates improves coping with workload in healthy subjects

Dietary components may affect brain function and influence behaviour by inducing the synthesis of neurotransmitters. The aim of the present study was to examine the influence of consumption of a whey protein-containing breakfast drink v. a carbohydrate drink v. control on subjective and physiological responses to mental workload in simulated work. In a randomised cross-over design, ten healthy subjects (seven women, median age 26 years, median BMI 23 kg/m(2)) participated in a single-blinded, placebo-controlled study. The subjects performed demanding work-like tasks after having a breakfast drink high in protein (HP) or high in carbohydrate (HC) or a control drink on separate sessions. Subjective states were assessed using the NASA Task Load Index (NASA-TLX), the Karolinska sleepiness scale (KSS) and the modified Profile of Mood States. Heart rate was recorded during task performance. The ratio of plasma tryptophan (Trp) to the sum of the other large neutral amino acids (LNAA) and salivary cortisol were also analysed. The plasma Trp:LNAA ratio was 30 % higher after the test drinks HP (median 0·13 (μmol/l)/(μmol/l)) and HC (median 0·13 (μmol/l)/(μmol/l)) than after the control drink (median 0·10 (μmol/l)/(μmol/l)). The increase in heart rate was smaller after the HP (median 2·7 beats/min) and HC (median 1·9 beats/min) drinks when compared with the control drink (median 7·2 beats/min) during task performance. Subjective sleepiness was reduced more after the HC drink (median KSS - 1·5) than after the control drink (median KSS - 0·5). There were no significant differences between the breakfast types in the NASA-TLX index, cortisol levels or task performance. We conclude that a breakfast drink high in whey protein or carbohydrates may improve coping with mental tasks in healthy subjects.

The effect of tryptophan on the cortisol response to social stress is modulated by the 5-HTTLPR genotype

OBJECTIVE

The S'/S' (S/S, S/Lg and Lg/Lg) variant of the serotonin (5-HT) transporter gene linked polymorphic region (5-HTTLPR) is associated with less efficient neurotransmission and may be more reactive to 5-HT manipulations. We tested the effects of l-tryptophan supplements on the cortisol response induced by a social stressor in S'/S' and L'/L' (La/La) carriers.

METHODS

In a double-blind parallel design, 25 S'/S' carriers and 21 L'/L' carriers were randomised to take l-tryptophan (2.8g/d) or placebo supplements for six days. At day 7 participants were exposed to the Trier Social Stress Test. Salivary cortisol and subjective mood states were monitored before, during and after the stress procedure.

RESULTS

S'/S' carriers who took l-tryptophan supplements had a significantly lower cortisol response to stress than S'/S' carriers who took placebo. Tryptophan had no effect on cortisol in L'/L' carriers and no effect on subjective mood states in either genotype group.

CONCLUSION

Tryptophan attenuates the cortisol response to acute social stress depending on 5-HTTLPR genotype. S'/S' carriers may indeed be more reactive to 5-HT manipulations.

Intrauterine growth retarded progeny of pregnant sows fed high protein:low carbohydrate diet is related to metabolic energy deficit

High and low protein diets fed to pregnant adolescent sows led to intrauterine growth retardation (IUGR). To explore underlying mechanisms, sow plasma metabolite and hormone concentrations were analyzed during different pregnancy stages and correlated with litter weight (LW) at birth, sow body weight and back fat thickness. Sows were fed diets with low (6.5%, LP), adequate (12.1%, AP), and high (30%, HP) protein levels, made isoenergetic by adjusted carbohydrate content. At -5, 24, 66, and 108 days post coitum (dpc) fasted blood was collected. At 92 dpc, diurnal metabolic profiles were determined. Fasted serum urea and plasma glucagon were higher due to the HP diet. High density lipoprotein cholesterol (HDLC), %HDLC and cortisol were reduced in HP compared with AP sows. Lowest concentrations were observed for serum urea and protein, plasma insulin-like growth factor-I, low density lipoprotein cholesterol, and progesterone in LP compared with AP and HP sows. Fasted plasma glucose, insulin and leptin concentrations were unchanged. Diurnal metabolic profiles showed lower glucose in HP sows whereas non-esterified fatty acids (NEFA) concentrations were higher in HP compared with AP and LP sows. In HP and LP sows, urea concentrations were 300% and 60% of AP sows, respectively. Plasma total cholesterol was higher in LP than in AP and HP sows. In AP sows, LW correlated positively with insulin and insulin/glucose and negatively with glucagon/insulin at 66 dpc, whereas in HP sows LW associated positively with NEFA. In conclusion, IUGR in sows fed high protein:low carbohydrate diet was probably due to glucose and energy deficit whereas in sows with low protein:high carbohydrate diet it was possibly a response to a deficit of indispensable amino acids which impaired lipoprotein metabolism and favored maternal lipid disposal.

Lack of effect of high-protein vs. high-carbohydrate meal intake on stress-related mood and eating behavior

Background

Consumption of meals with different macronutrients, especially high in carbohydrates, may influence stress-related eating behavior. We aimed to investigate whether consumption of high-protein vs. high-carbohydrate meals influences stress-related mood, food reward, i.e. 'liking' and 'wanting', and post-meal energy intake.

Methods

Participants (n = 38, 19m/19f, age = 25 ± 9 y, BMI = 25.0 ± 3.3 kg/m²) came to the university four times, fasted, once for a stress session receiving a high-protein meal, once for a rest session receiving a high-protein meal, once for a stress session receiving a high-carbohydrate meal and once for a rest session receiving a high-carbohydrate meal (randomized cross-over design). The high-protein and high-carbohydrate test meals (energy percentage protein/carbohydrate/fat 65/5/30 vs. 6/64/30) matched for energy density (4 kJ/g) and daily energy requirements (30%). Stress was induced using an ego-threatening test. Pre- and post-meal 'liking' and 'wanting' (for bread, filling, drinks, dessert, snacks, stationery (non-food alternative as control)) was measured by means of a computer test. Following the post-meal 'wanting' measurement, participants received and consumed their wanted food items (post-meal energy intake). Appetite profile (visual analogue scales), mood state (Profile Of Mood State and State Trait Anxiety Inventory questionnaires), and post-meal energy intake were measured.

Results

Participants showed increased feelings of depression and anxiety during stress (P < 0.01). Consumption of the test meal decreased hunger, increased satiety, decreased 'liking' of bread and filling, and increased 'liking' of placebo and drinks (P < 0.0001). Food 'wanting' decreased pre- to post-meal (P < 0.0001). The high-protein vs. high-carbohydrate test meal induced lower subsequent 'wanting' and energy intake (1.7 ± 0.3 MJ vs. 2.5 ± 0.4 MJ) only in individuals characterized by disinhibited eating behavior (factor 2 Three Factor Eating Questionnaire, n = 16), during rest (P ≤ 0.01). This reduction in 'wanting' and energy intake following the high-protein meal disappeared during stress.

Conclusions

Consumption of a high-protein vs. high-carbohydrate meal appears to have limited impact on stress-related eating behavior. Only participants with high disinhibition showed decreased subsequent 'wanting' and energy intake during rest; this effect disappeared under stress. Acute stress overruled effects of consumption of high-protein foods.

Trial registration

The study was registered in the Dutch Trial Register (NTR1904). The protocol described here in this study deviates from the trial protocol approved by the Medical Ethical Committee of the Maastricht University as it comprises only a part of the approved trial protocol.

General, Specific and Unique Cognitive Factors Involved in Anxiety and Depressive Disorders

Comorbidity among anxiety and depressive disorders is the rule rather than the exception. The Integrative Hierarchical Model proposes that each of these disorders contains general (common to all), specific (common to some) and unique components. However, research into this model is limited and hampered by small (clinical) sample sizes. The aim of the present study is to investigate the incremental validity of the cognitive constructs Anxiety Sensitivity, Pathological Worry and Cognitive Reactivity to sad mood over and above the personality traits neuroticism and extraversion. Symptomatic (N = 1,111) and remitted (N = 834) patients were selected from the 2,981 participants of the Netherlands Study of Depression and Anxiety (NESDA). Results revealed both specific and unique cognitive components of anxiety and depression. Across symptomatic and remitted groups, Anxiety Sensitivity was specific to social anxiety disorder and panic disorder, Aggression Reactivity was a unique component of dysthymia, and Rumination on Sadness was unique to major depressive disorder. We conclude that cognitive constructs have additional value in understanding anxiety and depressive disorders. Moreover, they prove to be more than mere epiphenomena of current disorders.

Influence of consumption of a high-protein vs. high-carbohydrate meal on the physiological cortisol and psychological mood response in men and women

Consumption of meals with different macronutrient contents, especially high in carbohydrates, may influence the stress-induced physiological and psychological response. The objective of this study was to investigate effects of consumption of a high-protein vs. high-carbohydrate meal on the physiological cortisol response and psychological mood response. Subjects (n = 38, 19 m/19f, age =25 ± 9 yrs, BMI  = 25.0 ± 3.3 kg/m²) came to the university four times, fasted, for either condition: rest-protein, stress-protein, rest-carbohydrate, stress-carbohydrate (randomized cross-over design). Stress was induced by means of a psychological computer-test. The test-meal was either a high-protein meal (En% P/C/F 65/5/30) or a high-carbohydrate meal (En% P/C/F 6/64/30), both meals were matched for energy density (4 kJ/g) and daily energy requirements (30%). Per test-session salivary cortisol levels, appetite profile, mood state and level of anxiety were measured. High hunger, low satiety (81 ± 16, 12 ± 15 mm VAS) confirmed the fasted state. The stress condition was confirmed by increased feelings of depression, tension, anger, anxiety (AUC stress vs. rest p < 0.02). Consumption of the high-protein vs. high-carbohydrate meal did not affect feelings of depression, tension, anger, anxiety. Cortisol levels did not differ between the four test-sessions in men and women (AUC nmol·min/L p > 0.1). Consumption of the test-meals increased cortisol levels in men in all conditions (p < 0.01), and in women in the rest-protein and stress-protein condition (p < 0.03). Men showed higher cortisol levels than women (AUC nmol·min/L p < 0.0001). Consumption of meals with different macronutrient contents, i.e. high-protein vs. high-carbohydrate, does not influence the physiological and psychological response differentially. Men show a higher meal-induced salivary cortisol response compared with women.

Effect of hydrolysed egg protein on brain tryptophan availability

Serotonin synthesis critically depends on plasma levels of tryptophan (TRP). Earlier studies have shown that for mood and cognitive benefits to occur, the ratio between TRP and other large neutral amino acids (LNAA) has to be increased by approximately 40 %. The present study investigated the dose-dependent effects of a TRP-rich hydrolysed protein (egg-protein hydrolysate, EPH) on the plasma TRP:LNAA. Moreover, it was investigated whether EPH could increase TRP:LNAA in the presence of 2 g of milk protein (MP). In a randomised double-blind crossover design, plasma amino acids were measured every 30 min for 3·5 h after ingestion of a drink containing either three different doses of 4, 8 and 12 g EPH containing 270, 560 or 800 mg of TRP, respectively, the combination of 4 g EPH and 2 g MP (74 mg TRP), or 4 g MP (148 mg TRP) in twenty healthy subjects with a mean age of 52 years. All three EPH doses caused significant increases of TRP:LNAA above 40 % at 30, 60 and 90 min after consumption in a dose-dependent manner. Compared with the 4 g EPH, the increase in TRP:LNAA in the 4 g EPH with 2 g MP condition was significantly lower at 60 min (63 v. 44 %, P < 0·001) and did not differ significantly at 90 min (58 v. 53 %, P>0·05). The present study showed that a low dose of 4 g EPH with even the addition of 2 g MP was sufficient to increase the ratio of TRP:LNAA above 40 %. Thus, EPH offers a viable ingredient to increase TRP availability.

Towards a neuroimaging biomarker of depression vulnerability

Major depressive disorder (MDD) is a pervasive and debilitating illness, with a recurrent course and chronic prognosis. Although effective treatments for MDD exist, there is a pressing need to characterize relapse vulnerability in order to design effective prophylactic care. To date, heterogeneity within depression neuroimaging research has made it difficult to establish a reliable biomarker of disorder susceptibility. In this paper, we review neuroimaging evidence for the assessment of MDD vulnerability, theorizing that current findings can be broadly distinguished between those indicating the presence of depressive episodes and those indicating MDD vulnerability during symptom remission. We argue that unlike the amygdala hyperactivity and prefrontal hypoactivity observed during MDD episodes, prefrontal hyperactivity may be a characteristic of dysphoric cognition during symptom remission that indicates MDD vulnerability and relapse risk. Drawing on current research of normative emotion regulation, we describe a potential test of MDD vulnerability, employing emotional challenge paradigms that induce cognitive reactivity — the increased endorsement of negative self-descriptions during a transient dysphoric mood. Relative to a normative model of prefrontal function, the neuroimaging assessment of cognitive reactivity may provide a reliable indicator of MDD vulnerability, advancing the field of biomarker research as well as the delivery of preventative treatment on an individual basis.

Tryptophan metabolism, from nutrition to potential therapeutic applications

Tryptophan is an indispensable amino acid that should to be supplied by dietary protein. Apart from its incorporation into body proteins, tryptophan is the precursor for serotonin, an important neuromediator, and for kynurenine, an intermediary metabolite of a complex metabolic pathway ending with niacin, CO(2), and kynurenic and xanthurenic acids. Tryptophan metabolism within different tissues is associated with numerous physiological functions. The liver regulates tryptophan homeostasis through degrading tryptophan in excess. Tryptophan degradation into kynurenine by immune cells plays a crucial role in the regulation of immune response during infections, inflammations and pregnancy. Serotonin is synthesized from tryptophan in the gut and also in the brain, where tryptophan availability is known to influence the sensitivity to mood disorders. In the present review, we discuss the major functions of tryptophan and its role in the regulation of growth, mood, behavior and immune responses with regard to the low availability of this amino acid and the competition between tissues and metabolic pathways for tryptophan utilization.

Psychological stress-induced, IDO1-dependent tryptophan catabolism: implications on immunosuppression in mice and humans

It is increasingly recognized that psychological stress influences inflammatory responses and mood. Here, we investigated whether psychological stress (combined acoustic and restraint stress) activates the tryptophan (Trp) catabolizing enzyme indoleamine 2,3-dioxygenase 1(IDO1) and thereby alters the immune homeostasis and behavior in mice. We measured IDO1 mRNA expression and plasma levels of Trp catabolites after a single 2-h stress session and in repeatedly stressed (4.5-days stress, 2-h twice a day) naïve BALB/c mice. A role of cytokines in acute stress-induced IDO1 activation was studied after IFNγ and TNFα blockade and in IDO1^−/− mice. RU486 and 1-Methyl-L-tryptophan (1-MT) were used to study role of glucocorticoids and IDO1 on Trp depletion in altering the immune and behavioral response in repeatedly stressed animals. Clinical relevance was addressed by analyzing IDO1 activity in patients expecting abdominal surgery. Acute stress increased the IDO1 mRNA expression in brain, lung, spleen and Peyer's patches (max. 14.1±4.9-fold in brain 6-h after stress) and resulted in a transient depletion of Trp (−25.2±6.6%) and serotonin (−27.3±4.6%) from the plasma measured 6-h after stress while kynurenine levels increased 6-h later (11.2±9.3%). IDO1 mRNA up-regulation was blocked by anti-TNFα and anti-IFNγ treatment. Continuous IDO1 blockade by 1-MT but not RU486 treatment normalized the anti-bacterial defense and attenuated increased IL-10 inducibility in splenocytes after repeated stress as it reduced the loss of body weight and behavioral alterations. Moreover, kynurenic acid which remained increased in 1-MT treated repeatedly stressed mice was identified to reduce the TNFα inducibility of splenocytes in vitro and in vivo. Thus, psychological stress stimulates cytokine-driven IDO1 activation and Trp depletion which seems to have a central role for developing stress-induced immunosuppression and behavioral alteration. Since patients showed Trp catabolism already prior to surgery, IDO is also a possible target enzyme for humans modulating immune homeostasis and mood.