Effects of alpha-lactalbumin on emotional processing in healthy women

Diet quality and anxiety: a critical overview with focus on the gut microbiome

Anxiety disorders disproportionally affect females and are frequently comorbid with eating disorders. With the emerging field of nutritional psychiatry, focus has been put on the impact of diet quality in anxiety pathophysiology and gut microbiome underlying mechanisms. While the relationship between diet and anxiety is bidirectional, improving dietary habits could better facilitate the actions of pharmacological and psychological therapies, or prevent their use. A better understanding of how gut bacteria mediate and moderate such relationship could further contribute to develop personalized programs and inform probiotics and prebiotics manufacturing. To date, studies that look simultaneously at diet, the gut microbiome, and anxiety are missing as only pairwise relationships among them have been investigated. Therefore, this study aims at summarizing and integrating the existing knowledge on the dietary effects on anxiety with focus on gut microbiome. Findings on the effects of diet on anxiety are critically summarized and reinterpreted in relation to findings on (i) the effects of diet on the gut microbiome composition, and (ii) the associations between the abundance of certain gut bacteria and anxiety. This novel interpretation suggests a theoretical model where the relationship between diet and anxiety is mediated and/or modulated by the gut microbiome through multiple mechanisms. In parallel, this study critically evaluates methodologies employed in the nutritional field to investigate the effects of diet on anxiety highlighting a lack of systematic operationalization and assessment strategies. Therefore, it ultimately proposes a novel evidence-based approach that can enhance studies validity, reliability, systematicity, and translation to clinical and community settings.

Alpha-lactalbumin and sleep: A systematic review

Insufficient sleep is a growing global problem, with poor sleep associated with many negative health and performance outcomes. Previous reviews investigating the effect of diet on sleep have highlighted the amino acid tryptophan as a promising sleep-promoting nutrient, with the richest food source of tryptophan, ⍺-lactalbumin, requiring further investigation. Therefore, this systematic review aimed to review the existing evidence of association between ⍺-lactalbumin and sleep. Four electronic databases (CINAHL Complete, Embase, MEDLINE Complete, and SPORTDiscus with Full Text) were searched from database inception to March 2023, with primary research articles included if they contained α-lactalbumin as an independent variable, an outcome measure of sleep or sleepiness, and participants were ≥ 18 years old. Eight studies were reviewed, with four studies recruiting athletic populations (50%) and four recruiting healthy participants (50%). Sleep or sleepiness was measured objectively in six studies (75%), with two studies employing polysomnography and four utilizing actigraphy to assess sleep. Across the studies, 20-60 g of ⍺-lactalbumin was supplemented, with five studies (63%) observing a positive association between α-lactalbumin and sleep. Sleep-onset latency was the primary sleep metric improved following evening supplementation of α-lactalbumin (≤ 3.5 hr pre-sleep), with no studies observing any negative associations with sleep. Data from this review suggest that individuals that have difficulty initiating sleep may benefit most from pre-sleep α-lactalbumin supplementation. Further research is required to establish the effect that α-lactalbumin has on sleep architecture, through the use of more comprehensive sleep analysis tools such as portable electroencephalography or polysomnography, in combination with stringent dietary controls.

Effects of α-lactalbumin on strength, fatigue and psychological parameters: a randomised double-blind cross-over study

PURPOSE

The neurotransmitter serotonin has a strong effect on behaviour and motor control. Regarding motor control, serotonin contributes to the development of fatigue and is also involved in the ability of motor neurones to operate across a large range of forces (gain control). The consumption of tryptophan-rich supplements (such as α-lactalbumin) is of interest because this amino acid is the only precursor for brain serotonin synthesis. Therefore, the purpose of this study was to determine the effects of α-lactalbumin supplementation on neuromuscular performance.

METHODS

Using a randomised double-blind cross-over design, 16 healthy participants performed plantar flexor and handgrip maximal voluntary contractions, a 30-s submaximal handgrip contraction, and a plantar flexor fatigue protocol before and 90 min after consuming either 40 g of α-lactalbumin, an isonitrogenous beverage (Zein) or an isocaloric beverage (corn-starch). Sleepiness, mood, and cognition were assessed to evaluate any psychological effects.

RESULTS

α-Lactalbumin decreased force steadiness by 25% during the sustained submaximal handgrip contraction (p < 0.01) and induced greater fatigue (15% reduction in total torque-time integral, p = 0.01) during the fatigue protocol. These effects were not observed for the other control beverages. No effects were found for maximal or explosive strength, or psychological measurements.

CONCLUSIONS

40 g of α-lactalbumin increased handgrip force variability and reduced performance during fatiguing muscle contractions but did not influence brief maximal contractions or psychological parameters in healthy individuals. These findings support the hypothesis that the consumption of α-lactalbumin can increase motor neurone input-output gain and exacerbate central fatigue during sustained maximal exercise.

The Antidepressant Effect of Deoiled Sunflower Seeds on Chronic Unpredictable Mild Stress in Mice Through Regulation of Microbiota–Gut–Brain Axis

Objectives

Sunflower seeds provide tryptophan-rich proteins with the potential to protect against depression. Tryptophan is a precursor of serotonin and a substrate for the production of indole derivatives by gut microbiota. This study aimed to investigate the association between the depression-alleviating effects of deoiled and dechlorogenic sunflower seeds (DSFS) and regulation of gut microbiota.

Materials and Methods

Male C57BL/6J mice were fed a diet comprising a source of soy protein (normal and model control), DSFS or whey protein concentrate (positive control) for 7 weeks, and chronic stress-induced depression was induced.

Results

Feeding the DSFS diet prevented depression-like behaviors, intestinal barrier damage, elevated plasma corticosterone, and reduced hippocampal serotonin levels in mice. Meanwhile, Feeding the DSFS diet significantly altered the gut microbiota structure, characterized by elevated relative abundances of Ileibacterium valens, Ruminococcus flavefaciens, Clostridium scindens, and Olsenella massiliensis, which were inversely associated with depressive behaviors and markers of mucosal barrier damage. DSFS also altered the gut metabolite profile, prevented depression-induced gut L-tryptophan depletion, and upregulated its metabolite indoleacetaldehyde.

Conclusion

Feeding the DSFS diet prevented depression in mice by remodeling the gut microbiota and bacterial tryptophan metabolism.

Breast Milk: A Source of Functional Compounds with Potential Application in Nutrition and Therapy

Breast milk is an unbeatable food that covers all the nutritional requirements of an infant in its different stages of growth up to six months after birth. In addition, breastfeeding benefits both maternal and child health. Increasing knowledge has been acquired regarding the composition of breast milk. Epidemiological studies and epigenetics allow us to understand the possible lifelong effects of breastfeeding. In this review we have compiled some of the components with clear functional activity that are present in human milk and the processes through which they promote infant development and maturation as well as modulate immunity. Milk fat globule membrane, proteins, oligosaccharides, growth factors, milk exosomes, or microorganisms are functional components to use in infant formulas, any other food products, nutritional supplements, nutraceuticals, or even for the development of new clinical therapies. The clinical evaluation of these compounds and their commercial exploitation are limited by the difficulty of isolating and producing them on an adequate scale. In this work we focus on the compounds produced using milk components from other species such as bovine, transgenic cattle capable of expressing components of human breast milk or microbial culture engineering.

Dietary α-Lactalbumin protects against thioacetamide-induced liver cirrhosis by maintaining gut-liver axis function in rats

We tested the hypothesis that α-lactalbumin inhibits the disruption of intestinal barrier function and liver cirrhosis by restoring gut-liver axis function in thioacetamide (TAA) -treated rats. Rat diets were supplemented with α-lactalbumin replacing 50% of dietary protein. After consuming α-lactalbumin for one week, rats were intraperitoneally injected with TAA twice a week for 14 weeks. The α-lactalbumin-enriched diet significantly inhibited the elevation of plasma alanine aminotransferase, aspartate aminotransferase, and hyaluronic acids. The supplement significantly reduced plasma lipopolysaccharide levels and increased occludin mRNA level. Hepatic fibrosis and regenerative nodules was developed and intestinal villi were shortened by TAA; α-Lactalbumin attenuated these histopathological changes. These results indicated that α-lactalbumin improved intestinal barrier function, suppressing endotoxin levels. These data also suggested that α-lactalbumin ameliorated the impairment of the gut-liver axis by TAA, inhibiting the development of liver cirrhosis.

Applications for α-lactalbumin in human nutrition

α-Lactalbumin is a whey protein that constitutes approximately 22% of the proteins in human milk and approximately 3.5% of those in bovine milk. Within the mammary gland, α-lactalbumin plays a central role in milk production as part of the lactose synthase complex required for lactose formation, which drives milk volume. It is an important source of bioactive peptides and essential amino acids, including tryptophan, lysine, branched-chain amino acids, and sulfur-containing amino acids, all of which are crucial for infant nutrition. α-Lactalbumin contributes to infant development, and the commercial availability of α-lactalbumin allows infant formulas to be reformulated to have a reduced protein content. Likewise, because of its physical characteristics, which include water solubility and heat stability, α-lactalbumin has the potential to be added to food products as a supplemental protein. It also has potential as a nutritional supplement to support neurological function and sleep in adults, owing to its unique tryptophan content. Other components of α-lactalbumin that may have usefulness in nutritional supplements include the branched-chain amino acid leucine, which promotes protein accretion in skeletal muscle, and bioactive peptides, which possess prebiotic and antibacterial properties. This review describes the characteristics of α-lactalbumin and examines the potential applications of α-lactalbumin for human health.

Tryptophan supplementation and serotonin function: genetic variations in behavioural effects

The neurotransmitter serotonin has a role in affective disorders such as depression and anxiety, as well as sleep, cognitive function and appetite. This review examines the evidence that serotonin-related genotypes may moderate the behavioural effects of supplementation with the serotonin precursor amino acidl-tryptophan (TRP), on which synthesis of serotonin (or 5-hydroxytryptamine; 5-HT) depends. However, 95 % of serotonin is synthesised and used in the periphery, and TRP is also metabolised via non-5-HT routes such as the kynurenine pathway. Moreover, understanding of genotypes involved in regulation of serotonin raises questions over the generalisability of TRP effects on behaviour across individuals with varied serotonergic genotypes. To date, only differences between variants of the 5-HT transporter-linked promoter region (5-HTTLPR) have been investigated in relation to behavioural effects of TRP supplementation. Effects of 5-HTTLPR genotypes are usually compared between the alleles that are either high (L/L′) or low (S/S′) expressing of mRNA for the 5-HT transporter receptor. Yet, another key genetic variable is sex: in women, the S/S′ genotype predicts sensitivity to improved mood and reduced cortisol by TRP supplementation, during stressful challenges, whereas the L/L′ genotype protects against stress-induced mood deterioration. In men, the L/L′ genotype may confer risk of stress-induced increases in negative affect; there are insufficient data to assess effects on male S/S′ genotypes. However, better-powered studies to detect sex by genotype by stress by TRP interactions, as well as consideration of more genotypes, are needed before strong conclusions and recommendations for behavioural effects of TRP treatment can be reached.

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.

No effect of oral L-tryptophan or alpha-lactalbumin on total tryptophan levels in breast milk

Postpartum depression (PPD) is the most common complication of childbearing with a 13% prevalence rate. Sleep disturbances are also common, particularly during early postpartum. In theory, l-tryptophan could improve sleep and reduce depressed mood in early postpartum; however, the first step in clinical development of tryptophan for use in postpartum is to measure the effect of oral l-tryptophan on its concentrations in breast milk, which is presently unknown. The aims were to investigate the effect of oral l-tryptophan and alpha-lactalbumin, a protein with high tryptophan concentration, on total and free tryptophan levels in breast milk and plasma, and to compare free tryptophan levels in breast milk with those in common infant formulas. Thirty healthy breastfeeding women were randomly allocated to receive 2g or 4g of l-tryptophan, or, 20g or 40g of alpha-lactalbumin or no supplement. Free tryptophan levels were also measured in 12 different infant formulas. Total tryptophan in breast milk was unaffected by oral administration of l-tryptophan or alpha-lactalbumin (repeated measures of ANOVA (rANOVA), group effect: p=0.93). Both l-tryptophan and alpha-lactalbumin were associated with greater free tryptophan levels in breast milk (rANOVA, group effect: p<0.001) (representing 2% of total tryptophan), but these concentrations were within the range of commonly used infant formulas. In contrast to most sleep inducing medications, l-tryptophan does not affect its total concentration in breast milk. These results support further investigation of dietary l-tryptophan and alpha-lactalbumin as part of a dietary supplementation approach to address sleep disturbances in postpartum and reduce risk of PPD.

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.

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.

Food-derived serotonergic modulators: effects on mood and cognition

The most frequently described drugs in the treatment of mood disorders are selective serotonin reuptake and monoamine oxidase (MAO) inhibitors, enhancing serotonin levels in the brain. However, side-effects have been reported for these drugs. Because serotonin levels in the brain are dependent on the availability of the food-derived precursor tryptophan, foods such as chicken, soyabeans, cereals, tuna, nuts and bananas may serve as an alternative to improve mood and cognition. Here we discuss the effects of high- or low-tryptophan-containing food, as well as plant extracts with a modest monoamine reuptake and MAO-A inhibition functional profile, on mood and cognition in healthy and vulnerable human subjects and rodents. Together the studies suggest that there is an inverted U-shaped curve for plasma tryptophan levels, with low and too high tryptophan levels impairing cognition, and moderate to high tryptophan levels improving cognition. This relationship is found for both healthy and vulnerable subjects. Whereas this relationship may also exist for mood, the inverted U-shaped curve for plasma tryptophan levels and mood may be based on different tryptophan concentrations in healthyv.vulnerable individuals. Animal studies are emerging and allow further understanding of effects and the mode of action of food-derived serotonergic components on mood, cognition and mechanisms. Ultimately, insight into the concentrations of tryptophan and other serotonergic components in food having beneficial effects on mood and cognition in healthy, but particularly vulnerable, subjects may support well-being in our highly demanding society.

Novel nutritional treatment for manic and psychotic disorders: a review of tryptophan and tyrosine depletion studies and the potential of protein-based formulations using glycomacropeptide

RATIONALE

Current amino acid (AA) mixtures used in acute tryptophan (Trp) and tyrosine (Tyr) plus phenylalanine (Phe) depletion and loading tests are unpalatable and lack specificity. Specificity is improved by reducing content of branched-chain amino acids (BCAA) and palatability to a certain extent by dose reduction.

OBJECTIVES

This study aims to identify a palatable naturally occurring alternative(s) to amino acids with the desired BCAA content for use in the above tests.

METHODS

A palatable alternative lacking in Trp, Tyr and Phe has been identified in the whey protein fraction caseino-glycomacropeptide (c-GMP). The absence of these three aromatic amino acids renders GMP suitable as a template for seven formulations for separate and combined depletion or loading and a placebo control. The absence of Phe and Tyr enables GMP to provide a unique nutritional therapy of manic and psychotic disorders by inhibition of cerebral dopamine synthesis and release and possibly also by enhancing glutamatergic function, in general, and in patients resistant to anti-psychotic medication, in particular.

RESULTS

Seven GMP-based formulations for the above tests are proposed, two of which can be used in the above nutritional therapy and a third formulation as a placebo control in clinical trials.

CONCLUSIONS

Development of these formulations should advance the above research and diagnostic tests, open new avenues for neuroscience research on monoamine function, and improve the therapy of bipolar and psychotic disorders and enhance the quality of life of sufferers.

The effects of native whey and α-lactalbumin on the social and individual behaviour of C57BL/6J mice

Milk proteins are the main components of everyday feeding and demonstrate a promising potential to change the mental condition. However, the effects of milk proteins after prolonged use remain poorly understood. The aim of the present study was to compare the effects of two whey proteins (alpha-lactalbumin (alpha-lac) and native whey) with casein on social and individual behaviour in mice. During a 30 d-long dietary intervention, male C57BL/6J mice had ad libitum access to an experimental diet containing 17% (w/w) of one of three protein sources: a-lac, native whey or casein. Mice had voluntary access to a running wheel. Social behaviour (group and resident-intruder activity) was tested at baseline and at the end of the intervention. Half of each dietary group was then withdrawn from the diet and running wheel for 7 d, and social activity and individual behaviour tests (open field, elevated-plus maze, light–dark box and forced swimming) were performed, to evaluate anxiety and depression-like status. The study shows that the long-term ingestion of whey proteins may modulate behaviour when compared with casein. Diet enriched with a-lac exhibited anxiolytic and antidepressive activities while the whey diet improved sociability. The differences between the diet groups were pronounced under the running wheel and the withdrawal of the experimental diet, suggesting that the beneficial effects of the milk proteins are clearer in stressful situations. Diet-induced behavioural changes remained visible for a week after feeding, which suggests that the proteins of the milk whey fraction have prolonged efficacy on the mental state of mice.

Dietary L-tryptophan supplementation with reduced large neutral amino acids enhances feed efficiency and decreases stress hormone secretion in nursery pigs under social-mixing stress

Tryptophan (Trp), the rate-limiting substrate of serotonin [5-hydroxytryptoamine (5-HT)] synthesis in the brain, competes with large neutral amino acids (LNAA) to cross the blood-brain barrier. This study was designed to evaluate the effect of L-Trp supplementation on nursery pigs experiencing social-mixing stress and fed diets varying in LNAA concentrations. Forty-eight individually housed barrows at 6 wk of age were randomly allotted to 4 dietary treatments based on a 2 × 2 factorial arrangement, with L-Trp supplementation (0 or 0.6%) and LNAA concentrations (4.5 or 3.8%) as the 2 main factors. Pigs were fed the diets for 7 d. On d 4, pigs within a treatment were paired in a new pen to create social-mixing stress and behavior was recorded for 24 h. Body weight was measured on d 0, 4, 5, and 7. Saliva and blood were collected on d 4 and 7. On d 7, pigs were killed to obtain hypothalami. During the entire period excluding the mixing day (d 5), L-Trp supplementation improved (P < 0.01) feed efficiency of pigs and lowering the LNAA further enhanced (P < 0.05) the effects of L-Trp. Supplementation of 0.6% L-Trp increased (P < 0.001) hypothalamic 5-HT and 5-hydroxyindoleacetic acid. The salivary cortisol concentration was reduced (P < 0.05) by lowering the LNAA. Collectively, lowering the LNAA further enhanced the improvement of feed efficiency by L-Trp supplementation of nursery pigs under social-mixing stress in association with reduced stress hormones, indicating that reducing LNAA in the diet can facilitate the effect of L-Trp on the stress response of pigs.

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.

Effect of different tryptophan sources on amino acids availability to the brain and mood in healthy volunteers

RATIONALE

Reduced brain serotonin function is acknowledged as a vulnerability factor for affective disturbances. Since the production of serotonin is limited by the availability of its plasma dietary amino acid precursor tryptophan (TRP), the beneficial effects of tryptophan-rich alpha-lactalbumin whey protein (ALAC) have recently been studied. The effects of ALAC remain rather modest, and alternative protein sources of tryptophan may be more effective.

OBJECTIVES

We tested whether hydrolyzed protein (HPROT) has greater effects on the plasma TRP/large neutral amino acids (LNAA) ratio and mood than intact ALAC protein in healthy volunteers.

MATERIALS AND METHODS

In a double-blind, randomized cross-over study, plasma amino acids and mood were repeatedly measured in 18 healthy subjects before and after intake of ALAC and HPROT as well as after placebo protein, pure tryptophan, and a tryptophan-containing synthetic peptide. Except for the placebo protein, all interventions contained 0.8 g TRP.

RESULTS

Significantly faster and greater increases in plasma TRP/LNAA were found after HPROT than after ALAC. In addition, the effects of HPROT on plasma TRP/LNAA were comparable with the effects of the tryptophan-containing synthetic peptide and even exceeded the effect of pure tryptophan. Sixty minutes after intake, mood was improved only following intake of HPROT and pure tryptophan, whereas longer-lasting mood effects were only found after intake of HPROT.

CONCLUSIONS

The use of a tryptophan-rich hydrolyzed protein source may be more adequate to increase brain tryptophan and 5-HT function compared with intact alpha-lactalbumin protein or pure tryptophan.

Dietary amino acids and brain serotonin function; implications for stress-related affective changes

Stress-related mood deterioration and affective disorders, such as depression, are among the leading causes of disease burden throughout the world, and are associated with severe medical consequences and mortality. Research has shown the involvement of dysfunctional brain serotonin (5-HT) biochemistry as a vulnerable biological factor in the onset of mood disturbances. Since the production of brain serotonin is limited by the availability of its plasma dietary amino acid precursor tryptophan, different foods and dietary amino acids that influence tryptophan availability are thought to alter affective behavior by changing brain 5-HT synthesis. Most dietary manipulation studies, however, reveal only modest affective changes, and note that these particularly occur in stress-prone or affected (sub-clinical) subjects. The current paper briefly summarizes evidence for the involvement of diminished brain serotonin function in affective disorders, discusses how this can be assessed and influenced by dietary manipulation procedures, and also notes how beneficial effects of dietary brain serotonin manipulation on affective behavior may be mediated by stress-induced brain serotonin vulnerability.