Brain Health: Neurodegeneration, Cognition & Mental Health

Citation model. Claims grounded in AllNutrition's trust-scored library carry an inline bracketed reference [n] linking to the References section, which lists each source's evidence level and AllNutrition trust score (0–1). Where an AllNutrition query returned an overall evidence_strength and consensus_level, those labels are surfaced in the Evidence Review so readers can calibrate confidence. Only sources actually returned by the tool are cited; no trust scores are invented.

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1. Introduction

Of all the organs nutrition touches, the brain is the one patients ask about with the most urgency and the least patience for nuance. "Will fish oil help my memory?" "Should I go keto for my mother's Alzheimer's?" "Is my diet causing my depression?" These are reasonable questions attached to an evidence base that is unusually heterogeneous in quality — ranging from one of the most rigorously proven diet-disease relationships in all of medicine (the ketogenic diet for drug-resistant epilepsy) to a booming field, "nutritional psychiatry," whose foundational trial is excellent but whose popular extrapolations often outrun the data.

This module surveys brain energetics, neuroinflammation, the gut-brain axis, and the blood-brain barrier (BBB) as the mechanistic scaffolding for three clinical domains: cognitive decline and dementia, neurodegenerative disease (Alzheimer's and Parkinson's), and mental health (principally depression). The organizing discipline, carried over from Module 01, is to keep observational dietary-pattern associations (Mediterranean and MIND diets, which are consistent and biologically plausible but rarely tested against dementia as a hard RCT endpoint) clearly separated from single-nutrient supplement trials (omega-3, B-vitamins, vitamin D), which are far more often null or context-dependent than the marketing around them suggests. A physician who finishes this module should be able to tell a family confidently what is established (keto for epilepsy, the biological plausibility and epidemiological consistency of Mediterranean-pattern eating for brain health), what is probable but incompletely proven (multidomain lifestyle intervention, anti-inflammatory dietary patterns and depression risk), and what remains genuinely uncertain (most single-nutrient supplementation for dementia prevention, the generalizability of the field's flagship depression trial).

2. Learning Objectives

By the end of this module, the learner will be able to:

1. Describe the neurovascular unit, cerebral glucose/ketone metabolism, and blood-brain barrier physiology, and explain how diet-related metabolic and inflammatory signals reach the brain.
2. Distinguish the strength of evidence for the Mediterranean/MIND dietary patterns (observational, consistent) from multidomain lifestyle RCTs (FINGER and successors, mixed replication) in dementia risk reduction.
3. Summarize randomized trial evidence for omega-3/DHA, B-vitamin/homocysteine-lowering, and vitamin D interventions on cognition, and explain why each is more nuanced than "supplement X prevents dementia."
4. Contrast the robust evidence for ketogenic diet therapy in drug-resistant epilepsy with the preliminary, guideline-discouraged evidence for ketogenic or ketone interventions in Alzheimer's disease.
5. Explain the "type 3 diabetes" hypothesis linking insulin resistance to Alzheimer's pathology, and describe the SMILES trial and the broader, still-maturing evidence base in nutritional psychiatry, including major confounding in ultra-processed-food-and-depression research.
6. Identify clinically relevant food-drug interactions in psychiatric and neurological care (notably MAOI-tyramine) and apply a calibrated, non-overstated framework when counseling patients on diet for brain health.

3. Scientific Foundations

3.1 Neuronal energetics and the glucose-to-ketone switch

The brain consumes roughly a fifth of resting energy expenditure despite being ~2% of body mass, almost entirely as glucose delivered via GLUT1 (across the BBB) and GLUT3 (neuronal). In Alzheimer's disease this system fails early: regional glucose hypometabolism is detectable on FDG-PET in cognitively normal, genetically at-risk (APOE-ε4) adults years before symptoms, and activity of key mitochondrial enzymes — pyruvate dehydrogenase complex (PDHC) and isocitrate dehydrogenase (IDH3) — falls by roughly 30% and 27% respectively in AD brain tissue [1][2]. This bioenergetic failure disproportionately harms synaptic transmission, the brain's most energy-hungry process, creating a feed-forward loop of declining synaptic activity and declining metabolic demand [2]. Astrocytes normally buffer this via the astrocyte-neuron lactate shuttle, but astrocytic support diminishes with aging [1]. This is the physiological rationale for ketogenic and ketone-based interventions: ketone bodies (beta-hydroxybutyrate) can supply neurons an alternative fuel when glucose transport and oxidation are impaired, and can improve mitochondrial ATP production and reduce reactive oxygen species [3][4]. Chronically elevated CSF lactate, by contrast, is a hallmark of AD and appears maladaptive rather than protective, illustrating that "alternative fuel" signaling in the aging brain is more complex than a simple glucose-versus-ketone binary [1].

3.2 Neuroinflammation and the dietary inflammatory index

Diet-derived pro-inflammatory signaling — from diets high in refined sugar, saturated fat, and ultra-processed ingredients — raises systemic markers (CRP, IL-6, TNF-α) that cross into the CNS and activate microglia. A high Dietary Inflammatory Index (DII) score is associated with a 47–50% higher risk of incident depression relative to the most anti-inflammatory diets across multiple independent cohorts, with a stronger association in women in at least one large cohort study [5][6][7]. Mechanistically, peripheral inflammation diverts tryptophan from serotonin synthesis toward the kynurenine pathway, generating neurotoxic metabolites (e.g., quinolinic acid), while also impairing hypothalamic-pituitary-adrenal (HPA) axis regulation and synaptic plasticity [6][7]. The same inflammatory signaling contributes to amyloid-beta accumulation and tau hyperphosphorylation in neurodegenerative disease, linking the depression and dementia literatures through a shared inflammatory pathway [7][8].

3.3 The gut-brain axis

Gut microbiota influence brain function through short-chain fatty acid (SCFA) production (notably butyrate, which reinforces both intestinal and blood-brain-barrier tight junctions), modulation of the vagus nerve, direct neurotransmitter synthesis (GABA, serotonin precursors) by specific bacterial strains, and regulation of systemic and neuro-inflammation [9][10]. "Psychobiotic" probiotic strains — Lactobacillus rhamnosus JB-1, Bifidobacterium longum 1714, Clostridium butyricum, among others — show antidepressant-like effects in randomized trials via HPA-axis dampening, cortisol reduction, and anti-inflammatory cytokine shifts, though effects are strain-specific and generally strongest as adjuncts to standard treatment rather than as monotherapy [9][11]. A Western diet, by contrast, depletes SCFA-producing taxa, increases circulating lipopolysaccharide (LPS), and produces measurable "leaky gut" that correlates with weakened BBB integrity and impaired hippocampal-dependent memory [10][12]. This gut-brain axis is examined in greater mechanistic depth in Module 26; here it functions as one of the primary conduits by which dietary pattern affects both depression risk and neurodegenerative disease.

3.4 The blood-brain barrier and neurovascular unit

The neurovascular unit — endothelial cells, pericytes, astrocytes, and tight-junction proteins (claudin-5, occludin) — controls what reaches brain parenchyma. Aging and Western-style diets reduce tight-junction protein expression, increasing BBB permeability and neuroinflammatory infiltration; saturated-fat- and sugar-heavy diets accelerate endothelial senescence and microvascular fragility, while fiber-driven SCFA production and diets such as Mediterranean/MIND appear protective of barrier integrity [12][13][14]. Time-restricted feeding preserved capillary density and BBB integrity in preclinical models, a proposed mechanism for lifestyle-based cognitive protection independent of weight change [3]. Notably, one exploratory human study found MIND diet adherence did not directly reduce gut-barrier permeability, but did moderate the downstream relationship between permeability and neuroinflammatory metabolites — evidence that dietary protection of the brain barrier system is real but partial and mechanistically incomplete [13].

3.5 Insulin resistance and the "type 3 diabetes" hypothesis

Type 2 diabetes roughly doubles Alzheimer's risk, and the combination of T2DM with the APOE-ε4 allele is associated with a substantially higher hazard than either alone [15][16]. The "type 3 diabetes" concept frames AD as a brain-specific insulin-resistant state: peripheral hyperinsulinemia saturates BBB insulin transporters, paradoxically starving the brain of insulin signaling; this disinhibits GSK-3β, driving tau hyperphosphorylation, while insulin-degrading enzyme (IDE) — shared between insulin and amyloid-beta clearance — preferentially degrades insulin under hyperinsulinemic conditions, allowing Aβ to accumulate [15][16]. Mitochondrial dysfunction and elevated ceramides further compound this energy-oxidation crisis [8][15]. Despite the mechanistic coherence, a large cohort study stratifying newly diagnosed T2DM patients by insulin sensitivity/secretion subtype found no statistically significant association between insulin-resistance subgroup and 10-year dementia incidence — a useful caution that mechanistic plausibility has outpaced clean epidemiological confirmation of the specific "type 3 diabetes" causal chain [17].

4. Clinical Relevance

Cognitive decline, dementia, and depression are among the most common reasons patients and families seek dietary guidance from physicians, and among the domains most vulnerable to overclaiming — by supplement marketers, by well-meaning clinicians extrapolating from mechanism, and increasingly by the "nutritional psychiatry" movement itself. A clinician who cannot distinguish the robust epilepsy-ketogenic-diet literature from the preliminary Alzheimer's-ketogenic-diet literature, or the SMILES trial's genuine signal from its overextension into "diet cures depression" messaging, risks both under-using a proven tool (multidomain lifestyle intervention, diet quality as an adjunct in depression) and over-promising benefit from unproven supplements. Calibrated counseling here — matching claim strength to evidence strength — is itself a form of harm reduction, protecting patients from costly, sometimes medically risky supplement regimens while still offering the genuinely actionable lifestyle levers the evidence supports.

5. Evidence Review

Established (high confidence):

• Ketogenic diet therapy for drug-resistant epilepsy achieves ≥50% seizure reduction in roughly 37–55% of children and ~43% of adolescents/adults, with generalized epilepsy responding better than focal (53% vs 14%); this is a mainstream, guideline-supported therapy requiring dietitian supervision for micronutrient risk. AllNutrition evidence_strength: strong, consensus_level: moderate [4][18].
• Mediterranean/MIND dietary pattern adherence is consistently, observationally associated with lower risk of cognitive decline, dementia, and Alzheimer's disease (approximate figures cited across reviews: 18% lower cognitive decline risk, 11% lower dementia risk, 30% lower AD risk), and with slower biological/brain aging in cohort and some RCT sub-studies (PREDIMED). AllNutrition evidence_strength: strong, consensus_level: mixed — consistent direction across designs, but causal RCT evidence on hard dementia endpoints remains limited [19][20][21].

Probable:

• Multidomain lifestyle intervention (FINGER model) improved global cognition, executive function, and processing speed in an at-risk Finnish cohort, but replication has been inconsistent: MAPT and PreDIVA did not replicate the effect, J-MINT (Japan) showed no cognitive benefit, while Maintain Your Brain and some Asian-cohort adaptations did show benefit, generally tracking adherence. AllNutrition evidence_strength: strong, consensus_level: moderate [22][23].
• A pro-inflammatory diet (high Dietary Inflammatory Index) is associated with meaningfully higher depression risk, and anti-inflammatory dietary patterns with lower risk, replicated across university-student, middle-aged, and older cohorts. AllNutrition evidence_strength: strong, consensus_level: mixed [5][6][7].
• Insulin resistance/type 2 diabetes as a risk factor for Alzheimer's disease ("type 3 diabetes" framing) is mechanistically well-supported (IDE competition, tau hyperphosphorylation, BBB insulin transport saturation), though direct epidemiological confirmation of the causal chain is mixed. AllNutrition evidence_strength: moderate, consensus_level: moderate [15][16][17].
• Psychobiotic probiotics as adjunctive therapy for depression and anxiety, with strain-specific, generally modest effects on mood scales and cortisol, mediated via HPA-axis and inflammatory pathways. AllNutrition evidence_strength: strong, consensus_level: moderate [9][11].

Emerging:

• Exogenous ketone supplementation shows modest but statistically significant cognitive improvement across healthy adults and MCI/AD populations in a recent systematic review/meta-analysis, potentially via ketone signaling effects on cerebral blood flow rather than fuel substitution alone — but this is a distinct, more positive signal than whole-diet ketogenic therapy for dementia, which guidelines currently discourage (see Controversial, below). AllNutrition evidence_strength: strong, consensus_level: moderate [3][10].
• Combined nutrient interventions (e.g., DHA + folic acid, multinutrient formulations) show more consistent cognitive benefit than single-nutrient supplementation in network meta-analysis, suggesting synergy is more important than any one "magic nutrient" [24][25].
• Time-restricted feeding for cerebrovascular/BBB preservation is a promising preclinical mechanism awaiting human confirmation [3].

Controversial:

• Ketogenic diet or MCT/ketone supplementation as a treatment for established Alzheimer's disease or MCI. The mechanistic rationale (bypassing impaired glucose metabolism) is strong, and small pilot trials are heterogeneous-to-positive, but the largest MCT RCT (>400 participants, 26 weeks) was null, and the 2024 ESPEN dementia guideline explicitly recommends against routine use, citing malnutrition risk in a frail population and lack of convincing clinical benefit (Grade B). AllNutrition evidence_strength: strong, consensus_level: moderate [3][26].
• B-vitamin/homocysteine lowering (VITACOG and successors) for cognitive protection. In MCI patients with elevated baseline homocysteine (≥11.3 µmol/L), 2 years of folate/B12/B6 produced a ~50% reduction in brain atrophy rate and memory gains — but the effect appears to require both elevated baseline homocysteine and adequate omega-3 status, and trials in normal-homocysteine populations or established AD are consistently null or even show increased adverse events. AllNutrition evidence_strength: strong, consensus_level: moderate [27][28].
• Omega-3/DHA supplementation for cognitive decline prevention. Positive signals cluster in APOE-ε4 carriers, MCI, and low-baseline-omega-3 individuals; the largest, best-controlled trial (365 participants, 24 months, high-dose DHA with confirmed CSF target engagement) found no cognitive or brain-volume benefit despite successfully raising brain DHA levels, and the VITAL trial (>4,000 participants) was also null. AllNutrition evidence_strength: strong, consensus_level: mixed [24][29].
• Vitamin D supplementation for dementia prevention. Observational associations (low vitamin D ↔ higher dementia/tau burden) are fairly consistent, but RCTs are contradictory — some positive at 800 IU/day, most higher-quality large trials (e.g., 400 IU/day in >4,000 women) null, and one large institutionalized-elderly study found no association between vitamin D status and cognitive decline at all. Routine supplementation for dementia prevention is not currently a guideline-endorsed indication outside of correcting frank deficiency. AllNutrition evidence_strength: strong, consensus_level: mixed [30][31].
• The generalizability of the SMILES trial and "nutritional psychiatry" as a field. SMILES demonstrated that a structured dietary counseling intervention improved depression outcomes versus social-support control, and this and related trials (including brief commercial-meal-delivery pilots) show real, if modest, signal for diet-quality improvement as a depression adjunct. However, critical reanalyses of Mediterranean-diet-and-depression cross-sectional data note very small effect sizes (e.g., explaining ~1.3% of variance in one university-student cohort) and caution that population messaging has outpaced trial-level certainty; large confirmatory RCTs (e.g., MEDIMIND) are still underway. AllNutrition evidence_strength: moderate, consensus_level: mixed [32][33][34].
• Ultra-processed food (UPF) intake and depression/mental health. The association is one of the more consistent findings in nutritional psychiatry, replicated across national and cohort samples, but every source explicitly flags that reverse causality (distress driving UPF consumption) and socioeconomic confounding cannot be excluded from current observational designs. AllNutrition evidence_strength: moderate, consensus_level: mixed [35][36][37].

Unsupported / overstated:

• Treating any single supplement (a specific omega-3 dose, a specific B-vitamin regimen, vitamin D alone) as a proven, general-population dementia-prevention or depression-cure strategy. The consistent pattern across this module's evidence is that benefit, where present, is concentrated in specific subgroups (deficient, high-risk-genotype, or elevated-biomarker individuals) rather than the general population [24][27][30].
• Extrapolating epilepsy-level ketogenic-diet efficacy to Alzheimer's disease; the ESPEN guideline explicitly counsels against this extrapolation given the different risk-benefit profile in a frail, malnutrition-prone population [26].

6. Practical Clinical Applications

When to consider a nutrition-based intervention:

• Drug-resistant epilepsy (children and adults): ketogenic diet therapy is an evidence-based option, ideally managed by a dietitian-led ketogenic diet team with micronutrient supplementation and metabolic monitoring [4][18].
• At-risk older adults for cognitive decline: counsel Mediterranean/MIND-pattern eating as a low-risk, plausibly beneficial lifestyle measure, and consider referral to or modeling of a multidomain program (diet + exercise + cognitive training + vascular risk management) in appropriately resourced settings, setting expectations based on the mixed FINGER-replication literature [19][22][23].
• MCI or early cognitive impairment with confirmed elevated homocysteine and adequate omega-3 status: B-vitamin supplementation (folate/B12/B6) is a reasonable, evidence-informed adjunct; check baseline homocysteine and B12/folate status first rather than empirically dosing everyone [27][28].
• Depression, particularly with poor baseline diet quality: structured dietary counseling toward a Mediterranean-type pattern is a reasonable adjunct to, not a replacement for, standard psychiatric care; omega-3 (500–2000 mg/day EPA/DHA) as adjunct to antidepressants has trial support, particularly with sertraline [24][32][33].
• Insulin resistance/T2DM with cognitive concerns: optimizing glycemic control and insulin sensitivity is a reasonable, mechanistically supported neuroprotective strategy even though the epidemiological causal chain to dementia is not fully confirmed [15][17].

When not to recommend / to counsel caution:

• Do not recommend ketogenic diets or MCT/ketone supplementation as a primary treatment for established dementia or Alzheimer's disease outside of a research protocol; current guidelines explicitly advise against this given malnutrition risk in frail elderly patients and lack of convincing benefit [26].
• Do not promise cognitive benefit from high-dose omega-3 or vitamin D supplementation in cognitively normal, nutritionally replete adults; the largest trials in this population are null [24][29][30][31].
• Avoid presenting Mediterranean-diet-depression associations as proven causal cures; frame as an evidence-supported adjunct with a modest, still-being-quantified effect size [32][33].

Drug and nutrient interactions:

• MAOIs and tyramine: the classic "cheese effect" hypertensive crisis risk remains real for aged cheeses, cured meats, soy sauce/miso, and tap beer; however, published evaluations of common dietary-restriction lists (including AI-generated ones) found significant inconsistency and over-restriction — verify guidance against a validated clinical reference rather than generic lists, and note that distilled spirits and fresh, unaged foods are generally lower risk than commonly assumed [38].
• Serotonergic supplements (St. John's Wort) plus SSRIs/SNRIs/MAOIs: risk of serotonin syndrome; screen for supplement use in any patient on serotonergic psychiatric medication [32][38].
• Ketogenic diet and hepatic drug metabolism: ketosis may alter cytochrome P450 activity, relevant for patients on polypharmacy or with hepatic comorbidity when a ketogenic diet is used therapeutically (e.g., for epilepsy) [38].
• Omega-3 at high doses and anticoagulation: bleeding risk with concurrent anticoagulant/antiplatelet therapy; use caution at doses above ~2–3 g/day [24].

7. Clinical Pearls

• Ketogenic diet for epilepsy and ketogenic diet for Alzheimer's are not the same evidence tier — one is standard of care, the other is guideline-discouraged outside research.
• "The MCI patient with elevated homocysteine" is the phenotype in whom B-vitamin therapy has trial support — not every older adult with memory complaints.
• A null high-dose DHA trial that successfully raised brain DHA levels is a powerful teaching point: target engagement does not guarantee clinical benefit.
• The SMILES trial is real and well-designed, but "diet cures depression" is a media extrapolation the trial itself does not support at that strength.
• Ultra-processed-food-depression associations are consistent but not yet causally proven; reverse causation (depression driving poor eating) is a live, unresolved competing explanation.
• Ask about herbal/psychobiotic supplement use in every patient on a serotonergic psychiatric medication — interactions are underrecognized.

8. Common Misconceptions

• "Fish oil prevents Alzheimer's." The largest, best-controlled trials in general and at-risk populations are null; benefit, where seen, clusters in specific subgroups (APOE-ε4 carriers, MCI, low baseline omega-3) [24][29].
• "If keto stops seizures, it should reverse Alzheimer's." Different disease, different risk-benefit calculus, and current guidelines advise against routine use in dementia [26].
• "Diet quality alone can substitute for antidepressant or psychotherapy treatment of major depression." The strongest trials in nutritional psychiatry test diet as an adjunct, not a replacement, and effect sizes in some observational literature are described by critical reanalyses as very small [32][33].
• "Low vitamin D definitely causes cognitive decline, so everyone should supplement." Observational association is consistent; RCT evidence for prevention is inconsistent and supplementation is not a guideline-endorsed general-population dementia-prevention strategy [30][31].
• "MAOI dietary restriction lists are all equally reliable." Published evaluation found significant inconsistency, including in AI-generated advice — verify against validated clinical pharmacology references [38].

9. Summary

Brain health nutrition spans one of medicine's most secure diet-disease relationships (ketogenic diet therapy for drug-resistant epilepsy) and one of its most actively contested emerging fields (nutritional psychiatry). Mechanistically, cerebral glucose/ketone metabolism, neuroinflammation, the gut-brain axis, and blood-brain-barrier integrity converge to explain why dietary pattern plausibly affects both cognitive decline and mood. Mediterranean and MIND dietary patterns show the most consistent observational protection against cognitive decline and dementia, though hard-endpoint RCT confirmation remains limited; multidomain lifestyle intervention (FINGER) showed a genuine signal that has not uniformly replicated. Single-nutrient supplementation — omega-3, B-vitamins, vitamin D — shows benefit concentrated in specific deficient or high-risk subgroups rather than the general population, and large, well-controlled trials are disproportionately null. The "type 3 diabetes" hypothesis linking insulin resistance to Alzheimer's is mechanistically compelling but not yet epidemiologically airtight. In mental health, the SMILES trial and the broader gut-brain-axis/psychobiotic literature provide genuine, moderate-strength evidence for diet as a depression adjunct, while ultra-processed-food-depression associations remain confounded by reverse causation and socioeconomic factors that current study designs cannot fully exclude. The clinician's task is to offer the genuinely supported levers — Mediterranean-pattern eating, glycemic control, targeted correction of documented deficiency, structured dietary counseling alongside standard psychiatric care — while resisting the field's persistent pull toward overclaiming.

10. References

Ordered by evidence strength / relevance. Evidence level and AllNutrition trust score (0–1) as returned by the tool.

1. ESPEN guideline on nutrition and hydration in dementia – Update 2024. Clinical Nutrition (2024). Guideline — trust 0.907.
2. Exploring ceramide as a novel biomarker and therapeutic target for Alzheimer's disease. Frontiers in Neuroscience (2026). Review — trust 0.9.
3. Time-restricted feeding rejuvenates cerebrovascular function and preserves cognition during aging. Research Square (2026). Observational/preprint — trust 0.863.
4. The efficacy and safety of ketogenic diet therapy among adolescents and adults with drug resistant epilepsy: A systematic review and meta-analysis. Seizure: European Journal of Epilepsy (2026). Systematic review — trust 0.86.
5. Dietary inflammatory potential in depressive symptoms in older Chinese people in Hong Kong: a cohort study. Frontiers in Nutrition (2026). Observational — trust 0.812.
6. Dietary inflammatory potential and depression in middle-aged and older adults. Journal of Affective Disorders (2025). Observational — trust 0.738.
7. Dietary Inflammatory Index and Depressive Symptoms in Chinese University Students: 3-Year Longitudinal Cohort Study. Journal of Medical Internet Research (2026). Observational — trust 0.75.
8. Metabolic Drivers of Alzheimer's Disease: Integrating brain hypometabolism, insulin resistance, and systemic dysregulation. Frontiers in Neuroendocrinology (2026). Review — trust 0.748.
9. A systematic review on gut microbiota consortium in the management of depression: Preclinical and clinical evidence. Psychoneuroendocrinology (2025). Systematic review — trust 0.877.
10. Effect of exogenous ketone bodies on cognition across health and disease: a systematic review and meta-analysis. Frontiers in Nutrition (2026). Systematic review — trust 0.842.
11. Neurobiological effects of microbial treatments within psychiatry: a systematic review. Frontiers in Psychiatry (2026). Systematic review — trust 0.842.
12. Western Diet and Cognitive Decline: A Hungarian Perspective. Nutrients (2025). Review — trust 0.715.
13. MIND-NL diet adherence moderates the relation of low-grade systemic inflammation with neuroinflammatory metabolites and cognitive functioning. Journal of Neuroinflammation (2026). Observational — trust 0.758.
14. Nutrition and gut–brain axis: opposing effects of dietary fiber and Western-style diets on Alzheimer's disease. Current Opinion in Clinical Nutrition and Metabolic Care (2026). Review — trust 0.7.
15. The Effect of Metabolic Syndrome on Alzheimer's Disease: Physical Activity as a Preventive and Therapeutic Measure. Brain Sciences (2026). Review — trust 0.85.
16. A convergence of global epidemics: diabetes as a modulator of neurodegenerative and neuro-inflammatory disorders. Frontiers in Neurology (2026). Review — trust 0.662.
17. Dementia Risk According to Indices of Insulin Sensitivity and Beta-Cell Function in Individuals With Newly Diagnosed Type 2 Diabetes: A Cohort Study. European Journal of Neurology (2026). Observational — trust 0.787.
18. Ketogenic diet therapies for the treatment of drug-resistant epilepsy in children and adults: A systematic review. PLOS ONE (2026). Systematic review — trust 0.713.
19. The role of the MIND diet in prevention and treatment of Alzheimer's disease: A literature review. Wiadomości Lekarskie Medical Advances (2026). Review — trust 0.627.
20. Effect of extra virgin olive oil on mild cognitive impairment and dementia in older adults: a systematic review and meta-analysis of clinical trials. Clinical Nutrition ESPEN (2026). Systematic review — trust 0.797.
21. Impact of Olive Oil Fatty Acids and Bioactive Compounds on Cognitive Function in Adults: A Systematic Review. Foods (2026). Systematic review — trust 0.762.
22. Multidomain interventions for healthy aging: From neuroplasticity to population health. Archives of Gerontology and Geriatrics (2025). Review — trust 0.723.
23. Baseline characteristics of the SINGER multidomain dementia prevention randomized controlled trial. Alzheimer's & Dementia (2026). RCT — trust 0.853.
24. Nutritional supplements and cognition in healthy aging and mild cognitive impairment patients: a systematic review and network meta-analysis. The Journal of Prevention of Alzheimer's Disease (2026). Systematic review — trust 0.79.
25. Marine-derived PUFAs and peptides for aging-related memory deficits. Frontiers in Nutrition (2026). Review — trust 0.613.
26. ESPEN guideline on nutrition and hydration in dementia – Update 2024 [ketogenic-therapy recommendation]. Clinical Nutrition (2024). Guideline — trust 0.907.
27. Vitamin deficiencies and Alzheimer's disease: evidence and implications for supplementation. Frontiers in Nutrition (2026). Review — trust 0.733.
28. Accelerated epigenetic aging as a modifier of homocysteine-associated cognitive decline: Findings from NHANES. Alzheimer's & Dementia (2026). Observational — trust 0.802.
29. CNS target engagement of high-dose DHA supplementation in older adults at risk for dementia: a randomised, double-blind, placebo-controlled trial. eBioMedicine (2026). RCT — trust 0.825.
30. Vitamin D and brain health: A systematic review. Clinical Nutrition Open Science (2026). Systematic review — trust 0.842.
31. Vitamin D Deficiency in Institutionalized Older Adults: Associations with Supplementation Practices but Not with Cognitive Decline or Dementia. Nutrients (2026). Observational — trust 0.752.
32. Biological Role of Nutrients, Food and Dietary Patterns in the Prevention and Clinical Management of Major Depressive Disorder. Nutrients (2022). Review — trust 0.677.
33. How strong is the evidence that the Mediterranean diet is an important factor in depressive symptomatology: A critical analysis. Nutrition (2026). Review — trust 0.703.
34. Meals that heal: a randomized controlled trial testing the feasibility of commercial meal delivery as a convenient dietary intervention for depression. Scientific Reports (2026). RCT — trust 0.853.
35. Ultra processed foods at the planetary nutrition nexus with implications for mental health. Discover Public Health (2026). Review — trust 0.727.
36. High ultra-processed food intake is associated with altered brain perfusion, depressive symptomatology, and increased inflammatory profile. Journal of Affective Disorders (2025). Observational — trust 0.737.
37. Consumption of ultra-processed foods and health status: a systematic review and meta-analysis. British Journal of Nutrition (2021). Systematic review — trust 0.755.
38. Inconsistent MAOI Dietary Guidance From Major AI Chatbots: A Brief Clinical Evaluation. Journal of Clinical Psychiatry (2026). Review — trust 0.75.

Supporting sources also surfaced: Adherence to the Mediterranean and MIND Diets and Parkinson's Disease Incidence in Women, E3N cohort (Annals of Neurology 2026, observational, trust 0.787); When bad turns good: cholesterol and LDL in Parkinson's disease systematic review (Neurological Sciences 2026, systematic review, trust 0.842); The Role of Diet in Parkinson's Disease (JPD 2024, review, trust 0.702); Bioactive Compounds in Coffee review (Molecules 2026, review, trust 0.705); Decoding psychotropic-induced metabolic disturbances: gut-brain axis review (Frontiers in Nutrition 2026, review, trust 0.715).