Three different clients, one week, same opening line: “I’ve done all the blood tests, changed my diet, tried every supplement… but I still can’t think straight.”
One was a teacher who couldn’t remember her students’ names. Another was a software developer who’d re-read the same line of code five times and still couldn’t process it. The third was a new mum who described her brain as “full of cotton wool.”
All had been told their thyroid was fine. Iron was decent. Vitamin D sorted. B12 adequate. And yet, they were all struggling to finish sentences, losing their train of thought mid-conversation, and forgetting why they’d walked into a room.
What changed when we looked deeper? The Organic Acids Test (OAT) consistently revealed functional issues that standard pathology simply doesn’t measure. Not because blood tests are useless, but because they’re only showing part of the picture.
In this article, I’ll share what the OAT actually tests, what I’ve learned from ordering dozens of them over the years, the specific markers I look at for brain fog, and whether it’s worth considering if your cognitive function is still struggling despite doing “all the right things.”
What Is an Organic Acids Test (And Why It’s Different from Standard Blood Work)?
The simple explanation: An Organic Acids Test is a urine test that measures the byproducts (metabolites) of various biochemical pathways in your body.
Think of it like this. Your body is constantly running complex chemical reactions: breaking down food for energy, making neurotransmitters, detoxifying substances, managing inflammation. Each of these processes leaves behind small molecular “footprints” that get excreted in urine. The OAT measures these footprints.
What it reveals that blood tests don’t:
- Functional capacity of your mitochondria (the energy powerhouses of your cells)
- Neurotransmitter production (dopamine, serotonin, noradrenaline)
- Gut bacteria activity (including yeast overgrowth and bacterial dysbiosis)
- Nutrient cofactor status (whether you’re actually using vitamins properly at a cellular level)
- Detoxification efficiency and oxidative stress load
Why urine matters here: Unlike blood tests, which show what’s circulating in your bloodstream right now, organic acids in urine reflect what your cells are actually doing with nutrients over time. It’s the difference between checking your bank balance (blood test) versus reviewing your transaction history (OAT).
The brain fog connection
Your brain is the most energy-demanding organ in your body. It represents about 2% of your body weight but uses roughly 20% of your total energy. When cellular energy production (ATP), neurotransmitter synthesis, or methylation pathways are compromised, cognitive function takes the hit first.
If your mitochondria aren’t working efficiently, if you’re not making enough dopamine, if your gut bacteria are producing neurotoxic compounds, or if chronic inflammation is creating oxidative stress… your brain simply doesn’t have what it needs to function clearly.
Standard blood tests won’t pick up these functional bottlenecks. They’re looking for disease. The OAT looks for dysfunction before it becomes disease.
(And if you’re already dealing with significant focus issues, you might find my article on supplements for ADHD, focus and brain fog helpful as a companion to this discussion.)
The Brain Fog Markers I Look at Most Often on an OAT
When a client comes to me with persistent brain fog, here are the specific sections of the OAT report I examine first:
1. Mitochondrial function markers (Citric Acid Cycle intermediates)
These include markers like citrate, aconitate, isocitrate, alpha-ketoglutarate, succinate, fumarate, and malate.
What they mean: How efficiently your cells are producing energy (ATP) through the Krebs cycle. This is the fundamental energy-generating system in every cell of your body.
Brain fog link: If mitochondria aren’t functioning properly, your brain literally doesn’t have enough fuel to maintain focus, memory, or processing speed. You might feel physically tired too, but the cognitive symptoms often hit harder and earlier.
Real example: I had a client whose OAT showed elevated citrate and alpha-ketoglutarate. This pattern pointed to B vitamin deficiencies (specifically B2, B3, and B5) blocking energy production at specific steps in the cycle. Her brain fog had been dismissed as “stress” for two years. Within six weeks of targeted B vitamin support and addressing her gut absorption issues, she described it as “someone lifted a veil.”
KEY POINT: Mitochondrial Dysfunction and Brain Fog
Your brain cells (neurons) are packed with mitochondria because they need constant, reliable energy. When mitochondrial function is impaired, you don’t just feel tired – you experience:
- Difficulty concentrating
- Slow processing speed
- Poor short-term memory
- Mental fatigue after cognitive tasks
- “Wired but tired” feeling
The OAT can reveal where in the energy production pathway things are getting stuck, allowing for much more targeted intervention than generic “energy support.”
2. Neurotransmitter metabolites
The OAT measures breakdown products of key neurotransmitters:
- HVA (homovanillate): Reflects dopamine turnover
- VMA (vanilmandelate): Reflects noradrenaline activity
- 5-HIAA: Reflects serotonin metabolism
- Quinolinate: A neurotoxic compound that can interfere with neurotransmitter function
What they show: Whether your brain is making enough of the chemicals needed for motivation, focus, mood stability, and mental clarity.
Brain fog link: Low dopamine turnover often shows up as lack of motivation, poor concentration, inability to start or finish tasks, and that “can’t be bothered” feeling even when you want to care. Low serotonin can contribute to low mood, which absolutely affects cognitive clarity. High quinolinate suggests neuroinflammation, which directly impairs thinking.
Real example: One of my clients had low HVA (dopamine metabolite) and elevated quinolinate. This combination suggested both dopamine deficiency and neuroinflammation contributing to her persistent “fuzzy head.” She’d been prescribed antidepressants twice, which hadn’t helped. Addressing gut inflammation, supporting dopamine precursors, and reducing neuroinflammatory triggers made a dramatic difference within 10 weeks.
3. Methylation markers
The main one here is FIGLU (formiminoglutamate).
What it indicates: How well your body is using vitamin B12 and folate for methylation – a process critical for neurotransmitter production, DNA repair, detoxification, and managing inflammation.
Brain fog link: Poor methylation means sluggish detoxification, inefficient neurotransmitter recycling, and increased inflammation. All of these contribute to cognitive dysfunction.
This is relevant whether or not you have MTHFR gene variations. (If you’re curious about MTHFR, I’ve written a detailed explanation here.) The OAT shows whether methylation is actually working, regardless of your genes.
4. Gut bacteria markers
These include:
- Arabinose and tartaric acid: Indicate yeast (Candida) overgrowth
- HPHPA: Suggests overgrowth of certain Clostridia bacteria species
What they reveal: Whether you have an overgrowth of yeast or specific bacterial strains that produce neurotoxic byproducts.
Brain fog link: These metabolites can cross into circulation and directly interfere with neurotransmitter function. Arabinose, for instance, can inhibit enzymes needed for energy production. HPHPA can interfere with dopamine synthesis. They’re literally clouding your thinking from the inside.
Real example: I had a client with sky-high arabinose who’d been dismissed by multiple doctors as “just stressed” and “probably depressed.” She wasn’t depressed. She had severe yeast overgrowth producing neurotoxic metabolites. We addressed it with a targeted antifungal protocol and dietary changes. Her brain fog lifted within three weeks. She cried during our follow-up because she’d been told for so long that it was “all in her head.”
It was in her head. Just not in the way they meant.
5. Oxidative stress and detoxification markers
Key markers include:
- 8-hydroxy-2-deoxyguanosine (8-OHdG): Indicates oxidative damage to DNA
- Pyroglutamate: Suggests glutathione depletion (your body’s master antioxidant)
What they indicate: How much oxidative damage is occurring in your cells and whether your body has enough antioxidants (especially glutathione) to manage it.
Brain fog link: Chronic oxidative stress leads to neuroinflammation, which directly impairs cognitive function. Your brain is particularly vulnerable to oxidative damage because it’s high in fat, uses a lot of oxygen, and has relatively modest antioxidant defenses compared to other organs.
If you’re dealing with profound exhaustion alongside brain fog, this article on fixing fatigue naturally covers the oxidative stress connection in more detail.
What I Actually Do With OAT Results (The Practical Bit)
Getting the test results is one thing. Knowing what to do with them is another.
Here’s my process:
Step One: Cross-reference with symptoms and health history
The OAT doesn’t work in isolation. I’m looking at:
- How the markers correlate with the client’s specific symptoms
- Their health timeline (when did things start, what else changed)
- Medication history (some medications affect these pathways)
- Dietary patterns
- Stress load and sleep quality
- Previous interventions (what’s already been tried)
An elevated marker might mean something different for someone with a history of gut infections versus someone who’s been on long-term antibiotics versus someone with chronic stress and poor sleep.
Step Two: Prioritise interventions based on patterns
I don’t throw 20 supplements at someone all at once. We work systematically, addressing the biggest bottlenecks first.
Common interventions based on patterns:
For mitochondrial dysfunction:
- Activated B complex (B2, B3, B5 especially)
- CoQ10 (ubiquinol form for better absorption)
- Magnesium glycinate
- L-carnitine
- Alpha-lipoic acid
(More on this in my article about mitochondrial energy support.)
For neurotransmitter imbalances:
- Amino acid precursors: tyrosine for dopamine, 5-HTP or tryptophan for serotonin
- Cofactors: vitamin B6 (P5P form), zinc, magnesium
- Sometimes herbal support depending on the pattern
For methylation issues:
- Methylcobalamin (active B12)
- Methylfolate (active folate)
- Betaine (TMG) for additional methyl donor support
- Addressing any gut absorption issues
For gut dysbiosis:
- Antimicrobials (herbal or prescription depending on severity): oregano, caprylic acid, berberine, or pharmaceutical antifungals if needed
- Probiotics (specific strains based on the dysbiosis pattern)
- Dietary changes (usually reducing sugar and fermentable carbs while treating)
- Gut repair nutrients once acute infection is addressed
For oxidative stress:
- Glutathione support: NAC (N-acetylcysteine), glycine, selenium
- Vitamin C (high dose, spread throughout day)
- Vitamin E (mixed tocopherols)
- Polyphenols from diet and targeted supplements
Step Three: Reassess and adjust
I typically recheck symptoms at 6-8 weeks and may retest the OAT at 3-6 months depending on initial severity and response to treatment.
Why precision matters: I’ve had clients come to me after wasting hundreds of dollars on expensive supplement protocols from other practitioners that didn’t address their actual bottlenecks. The OAT helps avoid that guesswork. You’re not throwing spaghetti at the wall hoping something sticks. You’re targeting specific dysfunctions.
The Clients Who Benefit Most (And Who Probably Doesn’t Need One)
Let me be honest about who I typically recommend the OAT for, because it’s not everyone.
Who I typically recommend OAT for:
- Brain fog that hasn’t responded to standard interventions (improved diet, better sleep hygiene, stress management, basic nutrient repletion)
- Chronic fatigue with significant cognitive symptoms (not just physical tiredness)
- History of gut issues (IBS, SIBO, suspected Candida overgrowth) alongside mental fog
- Suspected mitochondrial dysfunction (family history, post-viral fatigue, medication side effects from statins or other mitochondrial-toxic drugs)
- People who’ve been told “everything looks normal” on standard testing but clearly aren’t functioning normally
- Those who want targeted answers rather than years of trial-and-error supplementation
Who probably doesn’t need it (yet):
- Haven’t addressed the obvious basics: poor sleep (less than 6-7 hours regularly), high unmanaged stress, inflammatory diet (lots of processed food, sugar, trans fats), undiagnosed nutrient deficiencies
- Brain fog that’s clearly situational (started with a specific medication, improves dramatically on weekends, directly tied to an identifiable stressor like a toxic work environment)
- Budget is tight and standard functional pathology hasn’t been done yet (comprehensive thyroid panel including antibodies, full iron studies, vitamin D, B12, folate, homocysteine, fasting glucose and insulin)
- Recent acute illness (wait at least 6-8 weeks after infection before testing for accurate baseline)
The honest assessment: The OAT typically costs between $350-$450 AUD. That’s not nothing. I want clients to spend their money where it’ll make the biggest difference for them.
If you haven’t had comprehensive blood work yet, start there. If your sleep is a mess and you’re eating terribly, fix that first. The OAT is for when you’ve done those things and still aren’t getting answers.
(For more on when standard testing isn’t enough, see my article on hidden gaps in blood work.)
DECISION FRAMEWORK: Is OAT Right for You?
Consider OAT if:
- Brain fog significantly impacts your quality of life
- Standard blood tests are “normal” but you feel terrible
- You’ve addressed basics (sleep, diet, stress) without adequate improvement
- You have concurrent gut symptoms
- You want precision rather than guesswork
Wait on OAT if:
- You’re sleeping less than 6 hours per night
- Diet is still highly inflammatory (lots of processed food, sugar)
- Basic pathology hasn’t been done (thyroid, iron, B12, vitamin D)
- Budget is a significant barrier
- Obvious medical issues haven’t been ruled out (sleep apnea, coeliac disease)
The Limitations and Realities (What I Wish More Practitioners Would Discuss)
I’m a big advocate for functional testing when used appropriately, but I also think it’s important to be realistic about limitations.
It’s a snapshot, not a diagnosis
High levels of certain markers can have multiple causes. Interpretation requires clinical context. I don’t just look at the numbers; I look at the person in front of me, their health history, their symptoms, what else is going on.
False positives and negatives do happen
Dietary intake before testing can skew results. If you eat a lot of citrus fruit the day before, certain markers will be elevated. If you take high-dose vitamin C or B vitamins right before testing, it can affect results. This is why proper preparation matters.
Not all labs are equal
Quality control matters. Reference ranges matter. I only use labs with solid validation studies, consistent reporting, and good clinical support. Some cheaper options exist, but if the data isn’t reliable, you’ve wasted your money.
It won’t “fix” everything
Some clients get disappointed when addressing OAT findings improves their energy and focus by 60-70% but doesn’t completely eliminate brain fog. Usually this means there are other layers we still need to address: HPA axis dysfunction, undiagnosed sleep apnea, chronic mold exposure, undiagnosed autoimmunity, or deep-seated trauma affecting nervous system regulation.
The OAT is one piece of a larger puzzle. A valuable piece, but not the whole picture.
The follow-up matters more than the test itself
I’ve seen practitioners order OATs and then do nothing practical with the results. Or they throw 20 supplements at once without prioritizing. Or they don’t adjust the plan when initial interventions aren’t working.
My approach: Start with the biggest bottlenecks first (usually gut and mitochondria in my experience), reassess in 8-12 weeks, adjust the protocol based on response, and then move to the next layer if needed. Systematic, not scattergun.
Real Case: The Marketing Manager Who Got Her Brain Back
Let me share a case that illustrates how this works in practice.
Background: Emma was 34, working in a high-stress corporate marketing role. Over 18 months, her brain fog had progressively worsened. She couldn’t concentrate in meetings. She’d sit down to write an email and stare at the screen for 20 minutes without typing a word. By 3pm every day, she felt “drunk” – not tired exactly, but profoundly disconnected and unable to think.
She’d seen her GP multiple times. She was told it was stress and offered antidepressants, which she declined because she wasn’t depressed. She was frustrated, scared, and starting to worry she’d lose her job.
Previous testing:
- Thyroid panel: Normal (though only TSH was tested)
- Iron: Borderline low (ferritin 25)
- Vitamin D: Optimal after supplementation
- B12: Mid-range
She’d been supplementing iron for six months with no improvement in brain fog.
What the OAT showed:
Severely elevated arabinose and tartaric acid – indicating significant yeast (Candida) overgrowth
Multiple citric acid cycle intermediates elevated – mitochondrial dysfunction, likely secondary to neurotoxic compounds from the yeast
Low HVA – suggesting low dopamine turnover, which explained her motivation and focus issues
What we did:
- Antifungal herbal protocol: Oregano oil, caprylic acid, and berberine for six weeks
- Strict low-sugar diet: She resisted this at first (understandably), but when I explained that sugar was literally feeding the organisms producing neurotoxins, she committed
- Mitochondrial cofactors: Activated B complex, CoQ10, magnesium glycinate
- L-tyrosine: To support dopamine production
- Gut repair nutrients: After the antifungal phase, we added specific probiotics and gut-healing nutrients
The outcome:
Week 3: “I feel… clearer? Like the static is quieter.”
Week 6: “Brain fog is about 70% better. I can actually think again. I cried after a meeting where I presented without stumbling over my words.”
Week 12: “I feel like myself again. I didn’t realize how much I’d lost until I got it back.”
Six-month follow-up: We retested. Yeast markers had normalized. Mitochondrial markers had significantly improved. She was off most supplements at that point, maintaining results with diet, a basic multivitamin, and occasional oregano if she felt yeast symptoms creeping back (usually after travel or periods of higher sugar intake).
She also told me her chronic bloating had resolved, which she hadn’t even mentioned as a primary concern initially. (If bloating is an issue for you, this article covers the approaches I find most effective.)
Why this case worked: We had a clear target (yeast overgrowth), she was committed to the dietary changes, and we addressed both the infection and the downstream effects (mitochondrial dysfunction and neurotransmitter imbalances). The OAT gave us a roadmap instead of guessing.
My Honest Take: Is It Worth It?
After ordering dozens of OATs over the years, here’s what I’ve learned:
When I think it’s worth the investment:
- You’ve genuinely ticked off the basics (sleep, diet, stress management, basic nutrients)
- Symptoms are significantly impacting your quality of life
- You’ve been stuck for months or years without clear answers
- You want targeted answers rather than another year of trial-and-error supplementation
- You’re committed to actually implementing the recommended changes
When I suggest waiting:
- Budget is a genuine barrier and would cause financial stress
- Foundational work hasn’t been done yet (sleep hygiene, inflammatory diet still in place, basic blood work incomplete)
- There’s a more obvious underlying issue that needs addressing first (undiagnosed sleep apnea, untreated coeliac disease, unmanaged autoimmune condition)
The bigger picture
The OAT is one tool in a larger functional medicine toolkit. It’s most useful when combined with thorough case-taking, detailed symptom tracking, and willingness to implement changes systematically.
What I tell clients: “This test helps me work smarter with your biochemistry, but it doesn’t replace the fundamentals. Sleep, stress management, nutrient-dense eating, and regular movement still matter. This gives us precision on top of those foundations.”
If someone expects the OAT to be a magic bullet that means they don’t have to change anything else, they’re going to be disappointed. If they see it as a sophisticated diagnostic tool that helps target interventions more effectively, they’re usually very happy with the investment.
How to Move Forward If This Resonates
If you’re reading this thinking, “This sounds like exactly what I need,” here are your next steps:
Step one: Consider whether you’ve addressed the foundations. I know I keep coming back to this, but it matters. If you’re sleeping poorly, eating lots of processed food, and haven’t had basic blood work done, start there. The OAT will be more useful and cost-effective once those pieces are in place.
Step two: If you’ve done the basics and you’re still struggling, book a consultation where we can review your full health history, current symptoms, and previous testing. I’ll let you know honestly whether I think the OAT will add value for you specifically. Sometimes it will. Sometimes there’s a better place to start.
Step three: If we decide to proceed with the OAT, here’s what to expect:
- I’ll send you the test kit with detailed instructions
- You collect a first-morning urine sample at home (simple process)
- Results typically come back in 2-3 weeks
- We schedule a detailed results consultation (usually 60-90 minutes)
- We discuss results in context of your symptoms and history
- We create a staged, prioritized supplement and lifestyle plan
- We schedule follow-up to track progress and adjust as needed
The realistic timeline: Most clients see noticeable cognitive improvements within 6-12 weeks if we’re addressing the right underlying issues. Some see changes much faster (like Emma). Others take longer, especially if there are multiple layers to address.
You can learn more about my overall approach and what to expect working together here.
Final Thoughts: When Standard Testing Isn’t Enough
Here’s what I’ve come to understand after years of working with clients whose brain fog just wouldn’t shift:
It’s rarely just one thing. But the OAT can help identify which systems are most compromised and where to focus first, rather than guessing or trying to fix everything at once.
The clients who benefit most from this testing are the ones who’ve already done the groundwork. They’ve addressed sleep. They’ve cleaned up their diet. They’ve worked on stress management. They’ve supplemented basic nutrients. And they’re still not thinking clearly.
For those people, the OAT can be genuinely valuable. It’s not magic, but it’s precise. It turns “let’s try this and see” into “your mitochondria are struggling at these specific steps, let’s support them” or “you have significant yeast overgrowth producing neurotoxic compounds, let’s clear it.”
I still firmly believe that most people should start with the basics. You don’t need a $400 test to know that poor sleep, chronic stress, and blood sugar swings will wreck your focus. But when you’ve addressed those things and you still feel like your brain is wrapped in fog, like you’re “not quite there,” like you’ve lost cognitive sharpness that used to come naturally… that’s when functional testing like the OAT can make a real difference.
My role is to help you decide whether it makes sense for your situation, interpret the results in the context of your life and health history, and implement changes you can actually sustain. Not to sell you a test. But to help you get your brain back if that’s what’s needed.
Because living with persistent brain fog is exhausting and isolating. People don’t always understand why you can’t just “focus harder” or “think more clearly.” But when there are tangible biochemical reasons – when your cells aren’t making enough energy, when neurotoxic compounds are interfering with neurotransmitter function, when oxidative stress is creating neuroinflammation – there’s genuine relief in knowing it’s not “all in your head” in the dismissive sense.
It is in your head. But in a way that can be measured, understood, and addressed.
If you’re dealing with persistent brain fog despite having done “everything right,” I understand how frustrating that is. Sometimes we need to look deeper to find answers. Book a consultation and we’ll work out together whether this kind of testing makes sense for you, or if there’s a better place to start.
