Benefits
Mental and physical fatigue in ME/CFS (Cassileth 2022 open-label)
Cassileth 2022 (PMC9238249) non-randomized controlled trial in 76 ME/CFS patients showed AVERAGE 22.5-27.9% reduction in Chalder Fatigue Scale at 6 weeks vs historical placebo (Likert scoring, P<0.005). Both physical and mental fatigue improved. 1000 mg TID dose more effective than 500 mg BID. Limited by open-label design and historical placebo control — but ME/CFS is treatment-resistant condition with few options.
Long COVID fatigue (REGAIN 2024 mixed RCT results)
REGAIN trial (n=69 long COVID patients): PRIMARY ENDPOINT (Chalder Fatigue Questionnaire) was NOT MET — no significant difference between OAA and placebo on primary fatigue measure. SECONDARY ENDPOINTS: OAA group showed significantly greater improvements in DSQ-SF-measured fatigue and total symptom burden at day 21. MIXED RESULTS overall — fails primary outcome but shows benefit on secondary measures. Honest interpretation: insufficient evidence to confirm efficacy in long COVID despite earlier promising open-label data. Suggests effects may be modest or measure-specific.
TCA cycle intermediate / energy metabolism support
Mechanistic basis: oxaloacetate is a key TCA cycle intermediate — combines with acetyl-CoA to form citrate, kicking off energy production from substrates. Theoretical mechanism for fatigue relief in mitochondrial-dysfunction contexts (ME/CFS, long COVID, post-viral syndromes). Clinical translation incomplete despite biochemical plausibility.
Animal lifespan extension (preclinical)
Preclinical work in C. elegans showed oxaloacetate extended lifespan via AMPK/FOXO pathway activation. Mouse studies showed oxaloacetate mimics caloric restriction effects. Foundational interest in oxaloacetate as longevity supplement based on these animal findings. Human longevity translation has not been demonstrated.
Cognitive enhancement (preclinical/early)
Animal studies show oxaloacetate may protect against neurodegeneration and improve cognitive function in stress models. Mechanism via TCA cycle support and reduced glutamate excitotoxicity. Some preliminary human data in early Alzheimer's research but limited rigorous trials.
Mechanism of action
TCA (Krebs) cycle intermediate
Oxaloacetate combines with acetyl-CoA (from carbohydrate, fat, or protein metabolism) via citrate synthase to form citrate — the first step of TCA cycle. Each TCA cycle turn requires oxaloacetate regeneration. Theoretical mechanism: supplementing oxaloacetate could 'top up' TCA cycle capacity in conditions of mitochondrial dysfunction.
Gluconeogenesis intermediate
Oxaloacetate is also a key intermediate in gluconeogenesis (glucose synthesis from non-carbohydrate precursors). May contribute to glucose metabolism modulation. Relevance to clinical effects unclear.
Glutamate scavenging / excitotoxicity protection
Oxaloacetate combines with glutamate via aspartate aminotransferase (AST) to form aspartate + α-ketoglutarate. This pathway can reduce extracellular glutamate concentrations — relevant to glutamate excitotoxicity in neurological conditions. Mechanism for theoretical neuroprotective effects in stroke and traumatic brain injury research.
AMPK activation / caloric restriction mimetic
Animal evidence suggests oxaloacetate activates AMPK pathway and FOXO transcription factors — mimicking caloric restriction effects on lifespan. Mechanism for preclinical longevity findings. Clinical translation uncertain at typical supplemental doses.
NAD+/NADH ratio modulation
Oxaloacetate participates in malate-aspartate shuttle that transfers reducing equivalents across mitochondrial membrane. May modulate NAD+/NADH ratio — a key cellular energy/aging signal. Mechanism interesting but clinical relevance not established.
Clinical trials
Randomized double-blind placebo-controlled trial (Cassileth et al. 2024, PMC12313680). NCT05840237. Sponsor: Terra Biological LLC.
69 long COVID patients meeting ME/CFS-like criteria randomized to 2,000 mg/day anhydrous enol-oxaloacetate or placebo (white rice flour) for 42 days. Primary outcome: Chalder Fatigue Questionnaire (CFQ). Secondary: DSQ-SF, RAND-36 quality of life, DANA Brain Vital cognition, UP Time.
PRIMARY ENDPOINT NOT MET — no significant difference in CFQ-measured fatigue reduction between OAA and placebo. SECONDARY ENDPOINTS: OAA group showed SIGNIFICANTLY GREATER improvements in DSQ-SF-measured fatigue and total symptom burden at day 21. MIXED RESULTS — fails primary outcome but shows benefit on alternative measures. Honest interpretation: insufficient evidence of robust efficacy; effects may be modest or measure-specific. Important to acknowledge primary outcome failure.
Non-randomized open-label controlled trial (Cassileth et al. 2022). PMC9238249.
76 ME/CFS patients (73.7% women, median age 47) and 43 long COVID patients given anhydrous enol-oxaloacetate at varying doses (500-3000 mg/day) for 6 weeks. Compared to historical placebo (Chalder Fatigue Score Likert scoring).
ME/CFS patients showed average 22.5-27.9% fatigue reduction at 6 weeks vs historical placebo (P<0.005). Both physical and mental fatigue significantly improved. Higher doses (1000 mg TID) more effective than lower doses (500 mg BID). LIMITATIONS: open-label, non-randomized, historical placebo (not concurrent control). Foundational hypothesis-generating evidence that motivated REGAIN RCT. Effects in REGAIN were less robust than in this open-label trial.
Preclinical lifespan study (Williams DS, Cash A, Hamadani L, Diemer T 2009, Aging Cell 8(6):765-768, doi:10.1111/j.1474-9726.2009.00527.x).
C. elegans worms with oxaloacetate supplementation. Lifespan and AMPK/FOXO pathway activation measured.
Oxaloacetate EXTENDED lifespan in C. elegans via AMPK/FOXO pathway activation. Foundational preclinical evidence supporting interest in oxaloacetate as longevity intervention. Mechanism may relate to caloric restriction mimetic effects. Direct human translation has NOT been demonstrated; animal lifespan studies do not predict human longevity supplementation effects.
About this ingredient
Oxaloacetate (OAA, 2-oxosuccinic acid, oxaloacetic acid) is a 4-carbon dicarboxylic acid that is one of the most important metabolic intermediates in living cells — functioning in TCA (Krebs) cycle, gluconeogenesis, malate-aspartate shuttle, and amino acid metabolism. Found endogenously in every cell. Despite biological centrality, oxaloacetate is HIGHLY CHEMICALLY UNSTABLE in solution — decarboxylates rapidly to pyruvate, especially at neutral pH and elevated temperature.
This instability has historically prevented effective oral supplementation. ANHYDROUS ENOL-OXALOACETATE (AEO) — stabilized form developed by Alan Cash at Terra Biological LLC, marketed as benaGene (100 mg) for general supplementation and as Oxaloacetate CFS / 'medical food' for ME/CFS and long COVID. Anhydrous enol form is stable as solid, releases active oxaloacetate after dissolution.
Background interest in oxaloacetate accelerated after Cash and colleagues' 2009 C. elegans lifespan study (Williams 2009) demonstrating AMPK/FOXO-mediated longevity effects. Animal studies in mice showed caloric restriction-mimetic effects — leading to interest in oxaloacetate as 'longevity supplement.' Clinical research focus shifted to MITOCHONDRIAL FATIGUE conditions: ME/CFS (myalgic encephalomyelitis/chronic fatigue syndrome) and LONG COVID — both characterized by post-exertional malaise, profound fatigue, cognitive dysfunction.
Hypothesis: TCA cycle support might address mitochondrial dysfunction underlying these conditions. EVIDENCE: 2/5 reflects: (1) Cassileth 2022 PMC9238249 OPEN-LABEL ME/CFS trial showing 22-28% fatigue reduction (n=76, but historical placebo control), (2) REGAIN 2024 PMC12313680 RCT in long COVID — PRIMARY ENDPOINT NOT MET but secondary measures favorable, (3) Williams 2009 C. elegans lifespan study foundational, (4) animal mouse caloric restriction mimetic data, (5) clear biochemical mechanism (TCA cycle intermediate).
LIMITED BY: REGAIN's primary endpoint failure — most rigorous trial showed less robust effects than open-label predecessors; translation from C. elegans/mice to humans uncertain; small sample sizes; relatively short trial durations. SAFETY: Generally good at studied doses; long-term safety beyond 6 weeks not extensively characterized.
Best positioned as: (a) ME/CFS / LONG COVID adjunct for those willing to try novel approaches in treatment-resistant conditions (with appropriate epistemic humility about evidence quality), (b) GENERAL FATIGUE adjunct in mitochondrial-dysfunction contexts, (c) LONGEVITY supplement at lower doses (100-300 mg) for those interested in caloric restriction mimetic hypothesis, (d) NOT a primary therapy for ME/CFS or long COVID — these conditions need comprehensive medical care, (e) anhydrous enol-stabilized formulation (benaGene-type) preferred for stability. Honest framing: oxaloacetate is mechanistically interesting and shows hint of efficacy in fatigue conditions, but the most rigorous trial (REGAIN 2024) failed primary endpoint despite secondary measure improvements. Reasonable adjunct in treatment-resistant fatigue conditions where conventional options are limited; not a confirmed therapy.
Animal lifespan extension data does not translate to human longevity claims at this stage.