BRS1-1-1 - Amino-Acid Availability & Prioritisation
(Neurotransmitter Protein Requirements)
1. Mission & Overview + Dietary Levers
Mission
Ensure meal-level protein supply delivers the amino-acid foundation neurotransmitter pathways depend on.
Intervention Dominance: Diet-Dominant — Dietary Requirements
Human dietary tracer appearance and source-specific plasma profiles are not brain neurotransmitter or ADHD outcomes. No head-to-head superiority over all lifestyle or optimisation routes is established. Prominence concerns the mission-specific supply process; it is not a nutrient-benefit ranking.
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Indispensable amino-acid supply
-
Tryptophan
-
Tyrosine
No separate cofactors or substrates are listed here.
No mapping established.
Overview
Food protein supplies indispensable amino acids—the amino acids the body cannot make in sufficient amounts—including phenylalanine and tryptophan. [1] [3] Phenylalanine can also be converted to tyrosine. [4] After a protein meal, dietary phenylalanine appears in the circulation. [6] Tyrosine and tryptophan are precursors later signalling can use for dopamine, noradrenaline and serotonin. [2] Protein that covers those amino acids is the supported dietary route. [1] [3]
- Benefits: These amino acids, including tyrosine made from phenylalanine, are how meal protein supplies the pool that dopamine, noradrenaline and serotonin pathways draw on. [4] [2] That capacity is not evidence that extra protein improves attention or mood. [1] [6]
- Implementation Notes: Indispensable amino-acid supply and tryptophan are the dietary requirements; food protein supplies these amino acids. [1] [3] Tyrosine is made from phenylalanine, so it is not classed as an indispensable amino acid. [4] No neurotransmitter-targeted intake dose is established. [1] [6] Each meal does not have to supply the full set. [5]
- Biological Relevance: Those amino acids still have to cross into the brain before they are used to make dopamine, noradrenaline or serotonin - see PM2.
2. Primary Biological Effects
↑ circulating indispensable amino-acid supply, including phenylalanine that can be converted to tyrosine
3. Intervention Levers
- Minced rather than intact beef in the tested older-adult meal
No PM-specific preparation protocol is currently selected. The qualified preparation experiment and pending intervention disposition remain in SF5 — Food texture and amino-acid appearance and its Evidence & Audit assessment.
No PM1-specific lifestyle intervention is selected after this assessment. Exercise, sleep and hydration findings remain available in Evidence & Audit; no demonstrated absence of broader benefit is implied.
4. Mechanistic Basis + Scientific Findings (SFs 6)
Phenylalanine-4-hydroxylase (PAH) contributes to endogenous tyrosine supply. The established reaction is documented in Scientific Principles. UniProt C1 and Rhea C2 establish reaction identity, not an independent dietary cofactor admission.
Summary
Later signalling can use tyrosine and tryptophan only after those amino acids are available in the circulation. A protein meal is what puts dietary phenylalanine there, and phenylalanine can be converted to tyrosine. Brain entry and neurotransmitter synthesis come after that. Oral tyrosine supply has also been measured as a circulating concentration response, not as brain delivery.
SF1 — Dietary protein and amino-acid availability
Gorissen et al. (2020) [6] pooled human trials of labelled whey, casein and milk protein. About half of the dietary phenylalanine appeared in the circulation over five hours. Casein delivered a smaller fraction than whey or milk, a larger dose delivered more, and the older subgroup showed a lower fraction appearing within the measurement window. That pooled association does not establish uniform age-related impairment. The measured endpoint is plasma phenylalanine, not brain dopamine, noradrenaline or serotonin.
Supporting evidence: SF1 — Dietary protein and amino-acid availability.
SF2 — Diet-wide amino-acid adequacy does not require identical complete meals
Mariotti and Gardner (2019) [1] found that adult vegetarian diets which include protein-rich plant foods can meet protein and amino-acid requirements. Moughan and Lim (2024) [3] score protein quality by digestible indispensable amino acids, not by grams alone. Marsh et al. (2013) [5] state that varied plant proteins across the diet can cover that set, so complementary proteins do not have to share every meal.
Supporting evidence: SF2 — Diet-wide amino-acid adequacy does not require identical complete meals.
SF3 — Phenylalanine conversion and endogenous tyrosine supply
Matthews (2007) [4] shows that humans convert phenylalanine to tyrosine, mainly in the liver. Tyrosine is normally dispensable because of that conversion, and it can become conditionally indispensable when phenylalanine is limited. The curated PAH reaction records identify this conversion without establishing a separate dietary tyrosine requirement. UniProt C1; Rhea C2.
Supporting evidence: SF3 — Phenylalanine conversion and endogenous tyrosine supply. Established reaction identity: Scientific Principle — Phenylalanine hydroxylase reaction.
Scientific Principle — Downstream precursor identity is not a dietary efficacy result
Aquili (2020) [2] names tryptophan as the serotonin precursor and tyrosine as the dopamine precursor. Those names identify the amino acids in this pool. They do not show that a higher circulating supply raises brain serotonin or dopamine. Brain transport and downstream synthesis remain distinct from circulating provision.
Foundational provenance: Scientific Principle — Tyrosine and tryptophan precursor identities. Historical record: Scientific Principle — Downstream precursor identity is not a dietary efficacy result.
SF5 — Food texture and amino-acid appearance
Food structure can modify the time course and measured appearance of amino acids from an ingested protein source. In the matched beef-texture experiment, more dietary phenylalanine appeared in the circulation after mincing, but total plasma essential-amino-acid concentrations and muscle protein synthesis did not differ detectably. Dietary tracer appearance and total circulating concentration are different measurements; neither establishes greater brain precursor delivery. Pennings et al..
Supporting evidence: SF5 — Food texture and amino-acid appearance. The preparation SOP remains proposed, not admitted.
SF6 — Extrusion altered early amino-acid kinetics, not demonstrated total loss
Processing can alter the temporal response without demonstrating a change in total measured exposure. The tested extruded mycoprotein/pea blend changed selected early plasma amino-acid responses, while the integrated five-hour grouped responses were not significantly different. Unlike the beef experiment, this study did not use a dietary tracer; the endpoints must not be treated as interchangeable or as proof of equal absorption. Extrusion crossover.
Supporting evidence: SF6 — Extrusion altered early amino-acid kinetics, not demonstrated total loss. No extrusion-related SOP is admitted.
SF7 — Oral tyrosine and protein-containing meals contribute to plasma tyrosine
In eleven subjects, plasma tyrosine increased during a protein-containing dietary day and rose further with divided oral L-tyrosine. This supports provision to the circulating precursor pool. Plasma concentration does not measure dietary appearance flux, brain entry or catecholamine synthesis, and the small meal/supplement experiment does not establish a general food-effective dose or benefit from additional intake. [23]
Supporting evidence: SF7 — Oral tyrosine and protein-containing meals contribute to plasma tyrosine.
(Boundaries of the mechanism)
Competitive transport of amino acids across the blood–brain barrier is BRS1-FM1-PM2 — LAT1 Competitive Transport Modulation. Dopamine synthesis and signalling are BRS1-FM1-PM3 — Dopaminergic Signalling Regulation. Noradrenaline signalling is BRS1-FM1-PM4 — Noradrenergic Signalling. Serotonin signalling is BRS1-FM1-PM5 — Serotonergic Signalling Regulation.
(Integration within BRS1)
This mechanism supplies the circulating pool at the start of BRS1(FM1). Later mechanisms in that pathway draw on it. A shared key-constraint mapping is not established.
4.1 Scientific Findings (6)
Summary
Dietary protein supplies the circulating precursor pool; food structure and source can alter delivery kinetics without proving superior neurotransmitter function. Curated reaction identity, whole-diet adequacy and experimental intervention findings are distinguished below.
· Provisionally assessed · Evidence & Audit
Human tracer studies establish dietary delivery. Cross-study source/dose comparisons and variable age results require qualified interpretation.
What this means
Scope is circulating provision and the exact measured endpoint, not brain entry, neurotransmitter efficacy or a clinical recommendation.
Evidence confidence: · Provisionally assessed · Evidence & Audit
Finding ID: PM1-F1
Finding Statement: Dietary protein supplies phenylalanine to the human circulation, with delivery kinetics varying by the tested protein source, dose and meal context. The pooled age association is context-dependent, not proof that ageing uniformly impairs absorption or that greater availability increases brain neurotransmitters.
Synthesised Evidence Confidence: · Provisionally assessed · Evidence & Audit
Synthesis: The pooled dairy corpus establishes dietary tracer appearance but is not 18 independent research-group replications. Independent human source comparisons support context-dependent plasma responses. An individual exercise study and the newer six-source crossover did not show a uniform age-related decrement; plasma profiles and dietary tracer appearance are not identical measurements.
Synthesis Limitations: Mostly male dairy-tracer cohorts; between-study source/dose contrasts, nonrandomised age comparisons and different matrices limit generalisation. No brain transport, neurotransmitter or ADHD endpoint.
Evidence Considered:
- Study
- Pooled analysis of 18 randomised trials using intrinsically labelled whey, casein or milk protein.
- Population
- 602 participants, mean age 53 years. The age comparison used 82 young adults and 83 older adults.
- Result
- Dietary phenylalanine entered the circulation. Protein type, dose and age changed the fraction that appeared.
- Effect / Magnitude
- Mean appearance 50% ± 14% over five hours. Casein 45% ± 11%, whey 57% ± 10%, milk 65% ± 13%. Older adults 45% ± 10% versus young adults 51% ± 14%.
- Evidence Summary
- A protein meal delivers phenylalanine into the circulation, and the amount depends on the protein, the dose and age.
- Limitations
- Phenylalanine appearance is not the full indispensable set, not tryptophan, and not a brain or clinical endpoint.
- Evidence Source
- Bounded external search
- Reference
- [6]
- Study
- Independent Exeter programme; randomised double-blind six-period crossover, 12 young and 10 older adults, both sexes.
- Population
- Independent Exeter programme; randomised double-blind six-period crossover, 12 young and 10 older adults, both sexes.
- Result
- Source-specific plasma profiles; some non-animal sources produced higher essential-amino-acid responses than the tested milk beverage. Integrated responses did not show a uniform age decrement.
- Effect / Magnitude
- Source-specific endpoint and uncertainty: Small cohorts; composition and food matrix differ, so no isolated digestibility estimate or universal ranking follows.
- Evidence Summary
- Source-specific plasma profiles; some non-animal sources produced higher essential-amino-acid responses than the tested milk beverage. Integrated responses did not show a uniform age decrement.
- Limitations
- Small cohorts; composition and food matrix differ, so no isolated digestibility estimate or universal ranking follows. Independent of Maastricht pooled dairy corpus; age analyses and six visits within a person are not six independent replications.
- Evidence Source
- Bounded external search
- Reference
- [10]
- Study
- Young/older men, rest/exercise comparisons; 48 participants total.
- Population
- Young/older men, rest/exercise comparisons; 48 participants total.
- Result
- Dietary phenylalanine availability did not differ detectably with exercise although muscle incorporation increased.
- Effect / Magnitude
- Source-specific endpoint and uncertainty: Muscle utilisation is not circulating-pool enhancement; a nonsignificant contrast is not equivalence.
- Evidence Summary
- Dietary phenylalanine availability did not differ detectably with exercise although muscle incorporation increased.
- Limitations
- Muscle utilisation is not circulating-pool enhancement; a nonsignificant contrast is not equivalence. NCT00557388 is part of Gorissen2020; no double-counting.
- Evidence Source
- Bounded external search
- Reference
- [15]
Evidence Dependency:
- Shared sources with PM1-F1 and PM1-F2 are reused for distinct propositions, not independent replication. Pooled studies, thesis chapters and journal reports may overlap.
Mechanistic explanation: Dietary protein and amino-acid availability
Not scored · Evidence & Audit
Retain nutritional adequacy, but separate whole-diet coverage from acute food-specific kinetics.
What this means
Scope is circulating provision and the exact measured endpoint, not brain entry, neurotransmitter efficacy or a clinical recommendation.
Evidence confidence: Not scored · Evidence & Audit
Finding ID: PM1-F2
Finding Statement: Varied adult diets can provide digestible indispensable amino acids without requiring every meal to supply the full set. This nutritional-adequacy proposition does not establish an optimal neurotransmitter dose or demonstrate that all plant and animal foods have identical postprandial responses.
Synthesised Evidence Confidence: Not scored · Evidence & Audit
Synthesis: Existing vegetarian-diet and DIAAS reviews support adequacy across a varied diet. New human source and faba-bean studies qualify single-food composition/digestibility; they do not contradict adequate mixed diets. The recent systematic requirement review concerns quantitative requirements, not neurotransmitter enhancement.
Synthesis Limitations: Requirement reviews are not direct tests of neurotransmitter response or every possible plant diet. Energy sufficiency, variety, age and clinical context remain relevant.
Evidence Considered:
- Study
- Review of protein and amino-acid intakes from vegetarian and vegan diets in Western adults.
- Population
- Adults, including older adults, eating vegetarian or vegan diets. Children are discussed separately.
- Result
- Protein-rich plant foods can achieve protein and amino-acid adequacy in adults.
- Effect / Magnitude
- No single intake-response estimate. The result is adequacy against requirements, not a change in brain transmitters.
- Evidence Summary
- Dietary patterns can cover the indispensable amino acids this pool requires.
- Limitations
- Requirement coverage is not a plasma time course and not a neurotransmitter outcome.
- Evidence Source
- Inherited repository evidence
- Reference
- [1]
- Study
- Review of the digestible indispensable amino acid score a decade after its introduction.
- Population
- Not a new human trial. The score is applied to foods and diets.
- Result
- Quality depends on digestible indispensable amino acids.
- Effect / Magnitude
- No neurotransmitter effect size.
- Evidence Summary
- Coverage of those amino acids is the quality claim this mechanism can use.
- Limitations
- A scoring review does not measure circulating or brain amino acids.
- Evidence Source
- Inherited repository evidence
- Reference
- [3]
- Study
- Review of protein in vegetarian diets.
- Population
- People eating vegetarian diets.
- Result
- Completeness can be reached across the day rather than inside every meal.
- Effect / Magnitude
- No meal-level neurotransmitter measurement.
- Evidence Summary
- Each meal does not have to supply the full indispensable set.
- Limitations
- The review does not test brain precursor availability.
- Evidence Source
- Inherited repository evidence
- Reference
- [5]
- Study
- Systematic review of studies January 2000-May 2024; duplicate screening and risk-of-bias appraisal.
- Population
- Systematic review of studies January 2000-May 2024; duplicate screening and risk-of-bias appraisal.
- Result
- Evidence gaps in exact requirement estimates do not negate indispensable-amino-acid biology.
- Effect / Magnitude
- Source-specific endpoint and uncertainty: Not a PM-specific intake prescription, postprandial tracer experiment or neurotransmitter trial.
- Evidence Summary
- Evidence gaps in exact requirement estimates do not negate indispensable-amino-acid biology.
- Limitations
- Not a PM-specific intake prescription, postprandial tracer experiment or neurotransmitter trial. Review plus included studies are not independent replications.
- Evidence Source
- Bounded external search
- Reference
- [20]
- Study
- Healthy-human single-food tracer/intubation study, NCT05047757.
- Population
- Healthy-human single-food tracer/intubation study, NCT05047757.
- Result
- Individual amino-acid digestibility and limiting-amino-acid content differ; a single food score is not a whole-diet inadequacy diagnosis.
- Effect / Magnitude
- Source-specific endpoint and uncertainty: Ileal digestibility, systemic appearance and brain transport are distinct endpoints.
- Evidence Summary
- Individual amino-acid digestibility and limiting-amino-acid content differ; a single food score is not a whole-diet inadequacy diagnosis.
- Limitations
- Ileal digestibility, systemic appearance and brain transport are distinct endpoints. Different endpoint and protocol; no replication credit for a dairy-source comparison and no independence score assigned.
- Evidence Source
- Bounded external search
- Reference
- [19]
- Study
- Independent Exeter programme; randomised double-blind six-period crossover, 12 young and 10 older adults, both sexes.
- Population
- Independent Exeter programme; randomised double-blind six-period crossover, 12 young and 10 older adults, both sexes.
- Result
- Source-specific plasma profiles; some non-animal sources produced higher essential-amino-acid responses than the tested milk beverage. Integrated responses did not show a uniform age decrement.
- Effect / Magnitude
- Source-specific endpoint and uncertainty: Small cohorts; composition and food matrix differ, so no isolated digestibility estimate or universal ranking follows.
- Evidence Summary
- Source-specific plasma profiles; some non-animal sources produced higher essential-amino-acid responses than the tested milk beverage. Integrated responses did not show a uniform age decrement.
- Limitations
- Small cohorts; composition and food matrix differ, so no isolated digestibility estimate or universal ranking follows. Independent of Maastricht pooled dairy corpus; age analyses and six visits within a person are not six independent replications.
- Evidence Source
- Bounded external search
- Reference
- [10]
Evidence Dependency:
- Shared sources with PM1-F1 and PM1-F2 are reused for distinct propositions, not independent replication. Pooled studies, thesis chapters and journal reports may overlap.
Mechanistic explanation: Diet-wide amino-acid adequacy does not require identical complete meals
Not scored · Evidence & Audit
Established conversion chemistry; dietary admission and downstream catecholamine effects remain separate decisions.
What this means
Scope is circulating provision and the exact measured endpoint, not brain entry, neurotransmitter efficacy or a clinical recommendation.
Evidence confidence: Not scored · Evidence & Audit
Finding ID: PM1-F3
Finding Statement: Phenylalanine-4-hydroxylase (PAH) converts L-phenylalanine to L-tyrosine. This endogenous route contributes to tyrosine supply but does not make tyrosine absent from foods or establish an independent requirement for extra dietary tyrosine.
Synthesised Evidence Confidence: Not scored · Evidence & Audit
Synthesis: UniProt P00439 and Rhea 20273 establish reaction identity; the Matthews human kinetic review remains linked for physiological context. No new intake-response or clinical conclusion is inferred.
Synthesis Limitations: Curated enzyme annotation does not quantify whole-body dietary contribution or human brain catecholamine flux. Do not automatically add every PAH cofactor as a PM1-specific dietary requirement.
Evidence Considered:
- Study
- Overview of human phenylalanine and tyrosine tracer kinetics.
- Population
- Human tracer studies in people with ordinary hydroxylation and in disorders that block it.
- Result
- Phenylalanine is converted to tyrosine. The conversion depends on phenylalanine availability.
- Effect / Magnitude
- Kinetic rates are reviewed. No dietary dose for a brain catecholamine change is given.
- Evidence Summary
- Dietary phenylalanine can supply tyrosine through a conversion that has been measured in humans.
- Limitations
- Conversion kinetics are not brain dopamine or noradrenaline synthesis.
- Evidence Source
- Inherited repository evidence
- Reference
- [4]
Evidence Dependency:
- Shared sources with PM1-F1 and PM1-F2 are reused for distinct propositions, not independent replication. Pooled studies, thesis chapters and journal reports may overlap.
Mechanistic explanation: Phenylalanine conversion and endogenous tyrosine supply
Scientific Principle: Tyrosine and tryptophan precursor identities
· Provisionally assessed · Evidence & Audit
Supports SOP: Minced rather than intact beef in the tested older-adult meal
Texture affected source-specific tracer delivery, not every circulating or functional outcome.
What this means
Scope is circulating provision and the exact measured endpoint, not brain entry, neurotransmitter efficacy or a clinical recommendation.
Evidence confidence: · Provisionally assessed · Evidence & Audit
Finding ID: PM1-F5
Finding Statement: In a randomised crossover study of ten older men, 135 g minced beef produced greater six-hour dietary phenylalanine appearance than the same quantity of steak. Total plasma essential-amino-acid concentrations and muscle protein synthesis did not differ detectably between preparations.
Synthesised Evidence Confidence: · Provisionally assessed · Evidence & Audit
Synthesis: The matched-food crossover supports a preparation effect on dietary tracer appearance. Null total-concentration and muscle outcomes prevent a generic better-protein or neurotransmitter interpretation. The thesis and publication describe one dataset.
Synthesis Limitations: One small older-male trial; no independent replication of the exact matched-beef protocol was established in this assessment. No claim that all foods should be minced or that this improves attention.
Evidence Considered:
- Study
- Randomised crossover; ten older men, mean age 74 years; two visits at least 14 days apart.
- Population
- Randomised crossover; ten older men, mean age 74 years; two visits at least 14 days apart.
- Result
- More dietary phenylalanine appeared after mincing. Total plasma essential-amino-acid concentrations and muscle synthesis did not differ detectably.
- Effect / Magnitude
- Six-hour dietary phenylalanine appearance: minced 61% ± 3% versus steak 49% ± 3% (means ± SEM), P < 0.01; 12 percentage-point difference. No paired confidence interval calculated or inferred.
- Evidence Summary
- More dietary phenylalanine appeared after mincing. Total plasma essential-amino-acid concentrations and muscle synthesis did not differ detectably.
- Limitations
- Small single trial; mean estimates and standard errors available, paired effect interval not extracted; no equivalence claim for null outcomes. Single empirical dataset; thesis and journal article are the same experiment, not replications.
- Evidence Source
- Bounded external search
- Reference
- [9]
Evidence Dependency:
- Shared sources with PM1-F1 and PM1-F2 are reused for distinct propositions, not independent replication. Pooled studies, thesis chapters and journal reports may overlap.
Mechanistic explanation: Food texture and amino-acid appearance
· Provisionally assessed · Evidence & Audit
Preserve both temporal differences and the null integrated endpoint.
What this means
Scope is circulating provision and the exact measured endpoint, not brain entry, neurotransmitter efficacy or a clinical recommendation.
Evidence confidence: · Provisionally assessed · Evidence & Audit
Finding ID: PM1-F6
Finding Statement: In a randomised crossover of nine healthy young adults, the tested high-moisture-extruded mycoprotein/pea blend delayed selected early plasma amino-acid responses relative to the dry blend. Total five-hour grouped amino-acid availability was not significantly different; the study does not establish poorer overall nutrition for all meat alternatives.
Synthesised Evidence Confidence: · Provisionally assessed · Evidence & Audit
Synthesis: The human beverage experiment and in-vitro analyses address different endpoints. Selected phenylalanine/tyrosine peaks changed, while grouped integrated responses were statistically inconclusive. Composition, matrix and sampling constrain interpretation.
Synthesis Limitations: Single small trial, no dietary tracer, numerous secondary endpoints and laboratory reconstituted products. Not proof of equal total absorption or a reason to avoid all processed plant foods.
Evidence Considered:
- Study
- Randomised double-blind counterbalanced crossover; nine young adults, five men/four women; minimum five-day separation.
- Population
- Randomised double-blind counterbalanced crossover; nine young adults, five men/four women; minimum five-day separation.
- Result
- Extrusion delayed early responses and reduced selected peaks, including phenylalanine and tyrosine. Total five-hour grouped amino-acid availability was not significantly different.
- Effect / Magnitude
- Phenylalanine peak: dry blend 72 ± 3 versus extruded 58 ± 3 micromol/L, P=0.020; time to peak 32 ± 4 versus 83 ± 20 minutes, P=0.037 (means ± SEM). Total five-hour grouped amino-acid iAUC: no statistically significant difference; no equivalence bounds inferred.
- Evidence Summary
- Extrusion delayed early responses and reduced selected peaks, including phenylalanine and tyrosine. Total five-hour grouped amino-acid availability was not significantly different.
- Limitations
- Small single dataset; no tracer, many endpoints, uncertainty on paired differences; laboratory reconstituted products not every commercial meat alternative. Distinct study but same Exeter programme as nonanimal2024; not an independent replication of its six-source comparison.
- Evidence Source
- Bounded external search
- Reference
- [12]
Evidence Dependency:
- Shared sources with PM1-F1 and PM1-F2 are reused for distinct propositions, not independent replication. Pooled studies, thesis chapters and journal reports may overlap.
Mechanistic explanation: Extrusion altered early amino-acid kinetics, not demonstrated total loss
Supports oral supply to the circulating precursor pool.
What this means
A Type A supply proposition for this PM, distinct from LAT1 transport, brain synthesis or treatment.
Evidence confidence: Not yet scored
Finding ID: PM1-F7
Finding Statement: In the reported human experiment, plasma tyrosine increased over a protein-containing dietary day and rose further during oral tyrosine administration.
Synthesised Evidence Confidence: Not yet scored
Synthesis: Plasma tyrosine was measured in eleven subjects during protein-containing meals, with and without divided supplemental L-tyrosine.
Synthesis Limitations: Small human meal/supplement study. Plasma concentration is not dietary appearance flux, brain entry or catecholamine synthesis. Endogenous phenylalanine conversion remains an alternative; no general food-effective dose or extra-intake benefit. Primary abstract retrieved; full methods and risk-of-bias appraisal remain incomplete, so no numerical SEC is assigned.
Evidence Considered:
- Study
- Human dietary-day and oral tyrosine comparison.
- Population
- Eleven subjects.
- Result
- Higher plasma tyrosine during meals and a further supplement-associated rise.
- Effect / Magnitude
- No food-dose or brain-effect magnitude inferred.
- Evidence Summary
- Oral supply contributes to the circulating pool.
- Limitations
- Small human meal/supplement study. Plasma concentration is not dietary appearance flux, brain entry or catecholamine synthesis. Endogenous phenylalanine conversion remains an alternative; no general food-effective dose or extra-intake benefit.
- Evidence Source
- Bounded external search
- Reference
- [23]
Mechanistic explanation: Oral tyrosine and protein-containing meals contribute to plasma tyrosine
5. BRS Pathways and Connections
5.1 BRS Pathways
BRS1-FM1-PM1 — Amino-Acid Availability & Prioritisation ↓ BRS1-FM1-PM2 — LAT1 Competitive Transport Modulation ↓ BRS1-FM1-PM3 — Dopaminergic Signalling Regulation ↓ BRS1-FM1-PM4 — Noradrenergic Signalling
BRS1-FM1-PM1 — Amino-Acid Availability & Prioritisation ↓ BRS1-FM1-PM2 — LAT1 Competitive Transport Modulation ↓ BRS1-FM1-PM5 — Serotonergic Signalling Regulation
5.2 Cross-BRS Mechanism Relationships
Primary Mechanisms in other Biological Regulatory Systems that directly interact with, constrain or support this mechanism.
- BRS2(FM1) — Methylation Cycle Efficiency — Methylation uses methionine, another indispensable amino acid supplied by dietary protein. That is a shared amino-acid source, not a control this mechanism exerts on the methylation cycle.
5.3 Local BRS Mechanism Relationships
Related Primary Mechanisms within the same Biological Regulatory System that collectively support the integrated biological function.
- BRS1-FM1-PM2 - LAT1 Competitive Transport Modulation — The tyrosine and tryptophan in this circulating pool still have to enter the brain. That entry is competitive transport, not this supply step.
- BRS1-FM1-PM3 - Dopaminergic Signalling Regulation — Dopamine synthesis uses tyrosine after brain entry, including tyrosine made from phenylalanine. This mechanism supplies that precursor. It does not carry out the synthesis.
- BRS1-FM1-PM4 - Noradrenergic Signalling — Noradrenaline synthesis uses the same tyrosine after brain entry. This mechanism supplies the circulating precursor and does not regulate noradrenaline signalling.
- BRS1-FM1-PM5 - Serotonergic Signalling Regulation — Serotonin synthesis uses tryptophan from this pool. This mechanism supplies that indispensable amino acid and does not carry out serotonin synthesis.
7. Phenome Connections
These mappings are translational relationships, not single-mechanism outcome claims. Phenomes are emergent functional patterns supported by multiple interacting PMs across the BRAIN Framework.
Each Phenome relationship has two independent ratings. They are not combined or averaged.
Biology → Phenome Relationship Strength
How direct and important is this biological mechanism expected to be to the Phenome within the BRAIN model?
Evidence Confidence
How strongly does the adjudicated evidence support this particular biology → Phenome relationship?
- Biology → Phenome Relationship Strength: Low–Medium
- Evidence Confidence: Low–Medium
- Rationale: Meal protein supplies circulating phenylalanine, and phenylalanine can be converted to tyrosine. Tyrosine and tryptophan are precursors later catecholamine and serotonin pathways can use. These studies do not measure attention.
- Biology → Phenome Relationship Strength: Low–Medium
- Evidence Confidence: Low–Medium
- Rationale: Phenylalanine from dietary protein can be converted to tyrosine, the dopamine precursor. That supply is not a measurement of motivation or drive, and it is not dopaminergic signalling.
- Biology → Phenome Relationship Strength: Low
- Evidence Confidence: Low
- Rationale: Tryptophan is an indispensable amino acid and the serotonin precursor. Coverage of that amino acid is not a measurement of emotional regulation, and serotonin signalling is a later step.
Stage 2A/2B dietary-target assessment — 23 October 2026
ENRICHED. Meal-derived amino-acid appearance and circulating precursor availability.
Rechecked the 135 g minced-beef/steak crossover. Admit only the preparation-specific phenylalanine-delivery SOP in older men, retaining unchanged muscle-protein-synthesis findings. Individual EAA composition is food research, not nine new PM admissions. Tyrosine remains an existing biochemical candidate; the aggregate pool identity still needs reconciliation.
Assessment update: Earlier no-selected-SOP wording records the prior assessment; the qualified texture protocol added in this update is now independently assessed.
New implementation: 0 dietary-input admissions (0 completed Unset candidates), 1 practices, 0 biochemical participants, 0 unscored Findings. Existing accepted inputs, source assessments, mission, KCs, Phenome relationships and scores are retained.
Source-to-claim boundary: Assessment source. Stop after adjudicating the stated material candidate and tracing supported delivery. Keep uncertain specificity, formulation, anatomical or measurement links explicit; no negative evidence is inferred from incomplete retrieval.
8. References
- [1] Mariotti and Gardner (2019) — Dietary Protein and Amino Acids in Vegetarian Diets
- [2] Aquili (2020) — Tryptophan and Tyrosine as Serotonin and Dopamine Precursors
- [3] Moughan and Lim (2024) — Digestible Indispensable Amino Acid Score (DIAAS)
- [4] Matthews (2007) — Phenylalanine and Tyrosine Kinetics in Humans
- [5] Marsh et al. (2013) — Protein and Vegetarian Diets
- [6] Gorissen et al. (2020) — Dietary Protein and Circulating Phenylalanine
- [7] Food-processing systematic review and meta-analysis (2026)
- [8] Matthews et al. (2025): protein quality beyond DIAAS
- [9] Pennings et al. (2013): minced beef versus steak
- [10] Non-animal protein-source crossover (2024)
- [11] Dairy/vegetable blend versus single proteins (2019)
- [12] High-moisture extrusion crossover (2024)
- [13] Gorissen et al. (2014): carbohydrate coingestion
- [14] Milk fat with micellar casein (2017)
- [15] Pennings et al. (2011): exercise before protein
- [16] Res et al. (2012): protein before sleep
- [17] Even versus skewed protein distribution (2022)
- [18] Free amino acids versus intact milk protein (2021)
- [19] True ileal amino-acid digestibility of faba bean (2024)
- [20] Burstad et al.: systematic requirement review (2025)
- [21] Xin et al. (2026): exercise-induced dehydration and whey
- [22] Pennings et al. (2013) — Minced beef is more rapidly digested and absorbed than beef steak, resulting in greater postprandial protein retention in older men.
- [23] Melamed et al. (1980) — Plasma tyrosine in normal humans: effects of oral tyrosine and protein-containing meals
PM-local source records
- Food-processing systematic review and meta-analysis (2026). DOI: 10.1016/j.tifs.2026.105725. Original source. Access checked 2026-10-18. Publisher search abstract reports no pooled amino-acid-bioavailability effect; full text unavailable through publisher/Scite. No pooled estimate or risk-of-bias table assumed read.
- Matthews et al. (2025): protein quality beyond DIAAS. DOI: 10.1016/j.tjnut.2025.07.005. Original source. Access checked 2026-10-18. Open author institutional PDF: scope, metrics and processing discussion examined.
- Pennings et al. (2013): minced beef versus steak. DOI: 10.3945/ajcn.112.051201. Original source. Access checked 2026-10-18. Published abstract plus full experimental chapter 6 in the author institutional thesis; final published quantitative result cross-checked against author-shared publication.
- Non-animal protein-source crossover (2024). DOI: 10.1017/S0007114524000163. Original source. Access checked 2026-10-18. Scite full-text Methods and Results, including randomisation, washout, assays, power and multiplicity; published Cambridge PDF checked.
- Dairy/vegetable blend versus single proteins (2019). DOI: 10.3390/nu11112613. Original source. Access checked 2026-10-18. Scite full-text design, analytical methods and outcome definitions examined.
- High-moisture extrusion crossover (2024). DOI: 10.1016/j.tjnut.2024.05.018. Original source. Access checked 2026-10-18. Scite full-text human methods, composition, power/statistics and results examined.
- Gorissen et al. (2014): carbohydrate coingestion. DOI: 10.1210/jc.2013-3970. Original source. Access checked 2026-10-18. Published PubMed abstract examined; full methods not fully recovered in this pass.
- Milk fat with micellar casein (2017). DOI: 10.1016/j.clnu.2015.12.011. Original source. Access checked 2026-10-18. Publisher/PubMed abstract and institutional metadata recovered; no full-method risk-of-bias claim.
- Pennings et al. (2011): exercise before protein. DOI: 10.3945/ajcn.2010.29649. Original source. Access checked 2026-10-18. Published abstract and full institutional thesis chapter 2 examined.
- Res et al. (2012): protein before sleep. DOI: 10.1249/MSS.0b013e31824cc363. Original source. Access checked 2026-10-18. Published abstract retrieved; author-provided thesis and related older-adult study used for recovery leads, not substituted for full appraisal.
- Even versus skewed protein distribution (2022). DOI: 10.3390/nu14214442. Original source. Access checked 2026-10-18. Open article discovery, abstract and accessible publisher PDF sections checked; not a complete quantitative reanalysis.
- Free amino acids versus intact milk protein (2021). Original source. Access checked 2026-10-18. Complete published PubMed abstract; full methods not appraised.
- True ileal amino-acid digestibility of faba bean (2024). Original source. Access checked 2026-10-18. Full published abstract examined; detailed methods not scored.
- Burstad et al.: systematic requirement review (2025). DOI: 10.1016/j.ajcnut.2025.04.017. Original source. Access checked 2026-10-18. Publisher abstract and AHRQ/NCBI report discovery recovered. Journal full text unavailable through Scite; no quantitative tables assumed read.
- Xin et al. (2026): exercise-induced dehydration and whey. DOI: 10.3390/nu18193267. Original source. Access checked 2026-10-18. Publisher-indexed abstract, design and protocol excerpts recovered; direct HTML/PDF attempts failed. Do not claim full results or methods appraisal.
Curated biochemical references
- [C1] UniProtKB, Phenylalanine-4-hydroxylase (PAH), human, accession P00439, entry version 269 (2 September 2026); accessed 2026-10-18. Authoritative record. Return to Scientific Principle.
- [C2] Rhea 20273, phenylalanine hydroxylation reaction; accessed 2026-10-18. Authoritative reaction. Return to Scientific Principle.
Scientific Lesson
Dietary tracer appearance identifies amino acids arriving from the ingested food. Total plasma concentration also reflects endogenous turnover, tissue uptake and clearance. A higher tracer appearance or earlier peak is therefore not automatically a larger usable brain precursor supply, and neither establishes attention or mood benefit. SF1 — Dietary protein and amino-acid availability, SF5 — Food texture and amino-acid appearance, SF6 — Extrusion altered early amino-acid kinetics, not demonstrated total loss.
No validated structured conversion route is currently projected for this PM. This does not remove or reclassify its existing dietary inputs.
Mapping state: admitted-food-targets-resolved.