Why Alzheimer’s Is Called “Type 3 Diabetes” — And What That Means for Your Brain Right Now

By Dr. Marie Starling | The Healing Center Denver

Functional Medicine Doctor | Root Cause. Real Healing. You’re Not Broken.

Reading time: 8 minutes

Category: Brain Health | Hormones & Metabolism | Gut-Brain

The Diagnosis Nobody Talks About Until It’s Too Late

You’re standing in the kitchen. You came in here for something. What was it?

You’re mid-sentence and the word you need just… disappears. You know it. It’s right there. But you can’t reach it.

You’ve blamed stress. You’ve blamed aging. You’ve blamed being too busy.

But here’s what most doctors won’t tell you: these aren’t just annoyances. They can be early warning signals from a brain that is losing its ability to use fuel — years, sometimes decades, before anyone would call it dementia.

There is a name for this process. Researchers call it Type 3 Diabetes. And understanding it might be the most important thing you do for your long-term health.

So What Exactly Is Type 3 Diabetes?

You already know about Type 1 and Type 2 diabetes — both involve the body’s inability to properly manage insulin and blood sugar. Type 3 diabetes is different. It describes a condition where insulin resistance develops specifically inside the brain, impairing your neurons’ ability to take in and use glucose for energy.

Here’s the piece that changes everything: your brain produces its own insulin. It has its own insulin receptors. It runs its own metabolic system — somewhat independently of your pancreas and bloodstream.

When that system breaks down, your neurons start starving. Not because there isn’t enough sugar in your blood — your fasting glucose could look perfectly normal. But because the brain’s cells can no longer respond to insulin’s signal to open up and let the fuel in.

This relationship between impaired insulin signaling in the brain and Alzheimer’s disease is so well established that some researchers now call it “diabetes of the brain.” The term Type 3 Diabetes was first formally proposed in a landmark 2008 review and has been gaining traction in functional and integrative medicine circles ever since — even as conventional medicine continues to debate it.

Here’s what the research actually shows:

Emerging evidence frames Alzheimer’s disease within a metabolic context, implicating insulin resistance, impaired glucose metabolism, neuroinflammation, and oxidative stress as key drivers of neurodegeneration.

In other words: this is a metabolic disease. And metabolic diseases have metabolic roots.

The Mechanism: How Your Brain Starves

Let’s walk through exactly what happens when brain insulin resistance sets in — because this is where it gets both alarming and, more importantly, actionable.

Step 1: Insulin resistance develops in the brain. Just like in Type 2 diabetes, the brain’s insulin receptors become less sensitive over time. The signal gets weaker. Neurons stop responding.

Step 2: Neurons can’t take in glucose. Your brain is only 2% of your body weight but uses roughly 20% of your total glucose. When neurons can’t access that fuel, they begin to malfunction and eventually die.

Step 3: Amyloid plaques accumulate. An enzyme that normally breaks down insulin in the brain also breaks down amyloid proteins that can develop into plaques. When insulin levels are chronically elevated — as happens with insulin resistance — less amyloid gets broken down, leading to greater plaque buildup. This is one of the key hallmarks of Alzheimer’s disease.

Step 4: Tau tangles form. Synapses break. Without adequate energy, neurons lose their structural integrity. Tau proteins — which normally support the internal scaffolding of neurons — become abnormally folded. Communication between neurons breaks down.

Step 5: The brain shrinks. This isn’t metaphorical. Chronic cortisol exposure, neuroinflammation, and glucose starvation literally reduce brain volume — particularly in the hippocampus, the region responsible for memory and learning.

The result? Forgetfulness that feels like “normal aging.” Word-finding problems. Difficulty concentrating. Mood instability. Brain fog that no amount of sleep seems to fix.

And then, years later, a diagnosis.

“But My Blood Sugar Is Fine.” Here’s Why That’s Not Enough.

This is the part that frustrates me most as a functional medicine physician.

Standard metabolic bloodwork will tell you your fasting glucose, your HbA1c, maybe your fasting insulin. What it won’t tell you is whether your brain’s insulin signaling is intact. What it won’t tell you is whether your neurons are getting the fuel they need.

You can have a “normal” blood sugar panel and still have significant brain insulin resistance developing silently over years.

This is why the conventional medical model so consistently misses early cognitive decline. We’re checking the wrong things. We’re waiting for symptoms that are already late-stage consequences of a process that started 10, 15, even 20 years earlier.

Functional medicine asks different questions:

What is your fasting insulin (not just glucose)?
What does your HOMA-IR score look like — the ratio that reveals actual insulin sensitivity?
What’s happening with your inflammatory markers: CRP, homocysteine, IL-6?
How is your thyroid functioning? (Low thyroid directly impairs glucose metabolism in the brain.)
What’s the state of your gut microbiome? (The gut-brain axis is a major driver of neuroinflammation.)
Are you sleeping deeply enough for your brain’s glymphatic system to clear metabolic waste — including amyloid — every night?

These are the conversations that actually move the needle.

Why This Affects You Right Now — Not “Eventually”

Here’s what I want every patient who walks into The Healing Center Denver to understand:

Alzheimer’s doesn’t begin at 75. It begins in your 40s and 50s — or earlier.

Research shows people diagnosed with type 2 diabetes at a younger age face a higher risk of developing dementia than those diagnosed later in life. The earlier insulin resistance takes hold, the longer it has to do damage.

The brain fog you’re dismissing? The words you can’t find? The room you keep walking into and forgetting why? These are not quirks of a busy life. These are your brain telling you something is wrong with its metabolic environment.

This is not meant to scare you. It’s meant to wake you up — because the window to intervene is wide open right now, and it won’t always be.

The Root Causes Functional Medicine Targets

Unlike a drug that targets a single pathway, functional medicine asks: why did insulin resistance develop in the brain in the first place?

The answers are almost always a combination of these:

Chronic high sugar and refined carbohydrate intake Every spike in blood sugar drives an insulin surge. Over thousands of meals, over years, the receptors in the brain become numb to the signal. This is the most direct driver — and the most modifiable.
Neuroinflammation from a leaky gut The gut and brain are in constant communication via the vagus nerve, the immune system, and the bloodstream. When your gut lining is compromised — by stress, alcohol, NSAIDs, antibiotics, poor diet — inflammatory molecules called lipopolysaccharides (LPS) can cross into circulation and ultimately reach the brain. Activated brain immune cells (microglia) then begin a chronic low-grade inflammatory process that degrades insulin signaling.
Chronic cortisol elevation Cortisol is your stress hormone. It is also profoundly anti-insulin — it raises blood sugar, impairs insulin sensitivity, and, over time, literally shrinks hippocampal volume. If you are chronically stressed, your brain is chronically under assault.
Hormonal decline Estrogen, testosterone, progesterone, and DHEA all have direct neuroprotective effects. They support insulin sensitivity in the brain, reduce neuroinflammation, and promote synaptic plasticity. The hormonal shifts of perimenopause and andropause dramatically increase metabolic vulnerability in the brain — which is why cognitive symptoms so often emerge at this life stage.
Sleep deprivation Your brain has a waste clearance system called the glymphatic system that only activates during deep sleep. It literally flushes metabolic byproducts — including amyloid beta — out of brain tissue every night. Chronic poor sleep = chronic amyloid accumulation. This is not theoretical. It’s measurable.
Toxin burden Heavy metals (mercury, lead, aluminum), mold mycotoxins, and persistent organic pollutants directly impair mitochondrial function in neurons and disrupt insulin signaling. Toxic Alzheimer’s is its own subtype — and it is dramatically underdiagnosed because conventional medicine almost never tests for it.

What You Can Actually Do About It

This is where I diverge sharply from the standard narrative.

Conventional medicine’s response to Alzheimer’s has been to wait for plaques to form and then try to clear them with expensive drugs that produce modest benefit and significant risk of brain microbleeds. We’ll address the problems with that approach in a future post.

The functional medicine response is to change the metabolic environment of the brain before the damage becomes irreversible.

Here’s where to start:

Stabilize blood sugar first. Eliminate refined sugars and ultra-processed carbohydrates. Eat protein and healthy fat at every meal. Don’t skip breakfast — the morning glucose surge sets your metabolic tone for the entire day. Consider continuous glucose monitoring to see your actual patterns, not just a fasting snapshot.

Feed your brain what it can use. When glucose metabolism is impaired, the brain can use ketones as an alternative fuel — and ketones bypass insulin signaling entirely. This is why ketogenic and low-carbohydrate diets show genuine promise in early cognitive decline. MCT oil, in particular, rapidly converts to ketones and can cross the blood-brain barrier.

Heal your gut. A compromised gut is a compromised brain. Remove inflammatory foods (gluten, seed oils, ultra-processed foods), rebuild your microbiome with fermented foods and prebiotic fiber, and work with a functional medicine provider to test for gut dysbiosis, SIBO, and intestinal permeability.

Address your stress response — seriously. Nervous system regulation is not a soft skill. It is a metabolic intervention. HRV training, breathwork, adaptogenic herbs, sleep hygiene, and addressing root-cause cortisol dysregulation through comprehensive adrenal testing are all part of this.

Prioritize sleep architecture, not just sleep hours. Seven hours of fragmented light sleep is not the same as six hours of deep, restorative sleep. Magnesium glycinate before bed, eliminating blue light exposure in the evening, addressing sleep apnea (which dramatically accelerates neurodegeneration), and optimizing sleep temperature are all evidence-based starting points.

Get your hormones tested — properly. Not just TSH and a basic sex hormone panel. A full functional thyroid panel (TSH, free T3, free T4, reverse T3, thyroid antibodies). A DUTCH urine test for comprehensive sex hormone metabolites. DHEA-S. Pregnenolone. These are the hormones that protect your brain — and they deserve more than a cursory glance.

You Are Not Just “Getting Older”

Here’s what I want to leave you with.

The story you’ve been told — that memory loss is a natural consequence of aging, that there’s nothing to do but wait and hope — is not the full story. It’s the story that exists when we don’t look upstream. When we don’t ask why. When we treat symptoms instead of systems.

Framing Alzheimer’s disease as a metabolic condition opens up the possibility of preventive strategies and lifestyle modifications that could meaningfully change the disease’s trajectory.

You are not broken. Your biology is responding to inputs — inputs that, in many cases, can be changed.

The brain fog is a signal. The word-finding trouble is a signal. The room you keep walking into is a signal. And signals, when caught early enough, are gifts.

At The Healing Center Denver, this is exactly the work we do — not managing decline, but addressing the root causes that make decline more likely. If you’re ready to understand what’s actually happening in your brain and your body, we’d love to be in that conversation with you.

Frequently Asked Questions

Is Type 3 Diabetes an official diagnosis? Not yet — it is not currently recognized by the American Diabetes Association or major health organizations as a formal clinical category. But the underlying research linking brain insulin resistance to Alzheimer’s pathology is robust and growing, and many functional and integrative medicine clinicians use it as a clinical framework to guide prevention strategies.

Do I need to have diabetes to be at risk? No. You can have entirely normal blood sugar levels and still develop insulin resistance in the brain. The two systems are related but somewhat independent. This is precisely why standard metabolic panels miss this risk.

Can Alzheimer’s really be prevented? No one can guarantee prevention of any disease. But the evidence is strong that addressing metabolic, inflammatory, hormonal, and lifestyle root causes — especially early — meaningfully reduces risk and can slow or potentially reverse early cognitive decline. The ReCODE protocol developed by Dr. Dale Bredesen has demonstrated measurable cognitive improvement in early Alzheimer’s patients through exactly this kind of multi-pronged functional approach.

What testing should I ask for? At a minimum: fasting insulin, HOMA-IR, CRP (high-sensitivity), homocysteine, full thyroid panel, comprehensive sex hormone panel, vitamin D, omega-3 index, heavy metal screening, and a detailed gut assessment. At The Healing Center Denver, we offer comprehensive functional workups designed specifically around cognitive and metabolic health.

Dr. Marie Starling is a functional medicine doctor and the founder of The Healing Center Denver. Her practice focuses on identifying and treating root causes of chronic illness — including hormonal dysregulation, gut-brain dysfunction, neuroinflammation, and metabolic imbalance. She sees patients in Denver, Colorado and via telemedicine nationwide.

This blog is for educational purposes only and does not constitute medical advice. Please consult with a qualified healthcare provider before making changes to your health regimen.

Ready to understand what’s actually happening in your brain? Book a discovery call to start the conversation.

Root Cause. Real Healing. You’re Not Broken.