By the time your doctor diagnoses you, the damage has been accumulating for two decades. Here’s what they should have been testing for the entire time.
I want to tell you something that no doctor ever told me before I started reading the research.
Pre-diabetes is not the early stage of type 2 diabetes. It is the late stage of insulin resistance.
That distinction is going to seem academic at first. It is not. It is the difference between a disease that’s diagnosed in time to fully reverse, and a disease that’s diagnosed after twenty years of silent damage to your blood vessels, your nerves, your kidneys, your eyes, your liver, and — as the most recent research is making clear — your brain.
I coach clients to improve their health, their fitness, and their bodies. Many of them come to me already on metformin, on insulin, on Ozempic or Mounjaro, on prescriptions for type 2 diabetes that they were told they’d be on for the rest of their lives. The single most consistent pattern I see in their histories is this: their fasting glucose was “normal” for years before their diagnosis. Their HbA1c was “fine.” They were told to “watch their sugar.” Their doctors ran the same two tests every visit and watched the numbers slowly climb.
What none of those doctors did — not one, in dozens of charts I’ve reviewed — was order a fasting insulin.
That single test would have caught the disease ten, fifteen, even twenty years before the diagnosis ever came. And it would have caught it at a stage where it was completely, structurally reversible. Instead, the disease was missed entirely, allowed to progress, and only flagged once the pancreas itself was failing.
This series is about how type 2 diabetes actually develops, what your standard panel isn’t catching, what the disease is actually doing to you while no one is watching — and, critically, that the disease is curable in the majority of patients diagnosed in the last six years. The medical establishment now has the trial data to prove it. They just haven’t built the patient conversation around it yet.
We start here.
The 24-year head start
When a patient walks into a typical primary care appointment, the diabetes screening tests are fasting glucose and HbA1c. Fasting glucose under 100 is “normal.” Between 100 and 125 is “pre-diabetic.” 126 or above on two separate readings is “diabetes.” HbA1c follows roughly the same gradient: under 5.7% is normal, 5.7 to 6.4% is pre-diabetic, 6.5% or higher is diabetic.
Both of these tests measure the same thing: how much glucose is currently in your blood, or has been in your blood on average over the last two to three months. Neither of them measures how hard your pancreas is working to keep that number normal.
That distinction is everything.
Research now shows that elevated insulin levels can precede high glucose levels by as much as 13 years, and hyperinsulinemia can signal glycemic dysfunction up to 24 years in advance. Twenty-four years. Two full decades of metabolic dysfunction operating completely undetected by the standard screening tests.
The mechanism is straightforward once you understand it. Insulin is the hormone your pancreas releases in response to rising blood glucose. Its job is to push glucose into cells for energy or storage. In a metabolically healthy person, a small amount of insulin produces a large response, glucose drops back to baseline within a couple of hours, and insulin drops back to baseline shortly after.
In a metabolically dysfunctional person, the cells start responding less effectively to insulin. The pancreas compensates by releasing more insulin — sometimes two, three, even five times the normal amount — to achieve the same glucose-lowering effect. The system buys time. Glucose stays in the normal range. The patient feels fine. The standard labs come back clean.
But the pancreas is now working overtime. The beta cells — the specialized cells in the pancreas that produce insulin — physically grow in number to meet the demand. The patient is now in a state of chronic hyperinsulinemia. They are not yet pre-diabetic by any standard test. They are also not metabolically healthy. They are somewhere in between, in a phase that has no formal medical name and no standard screening.
That phase typically lasts ten to twenty years. The patient ages through it. They gain weight. They develop high blood pressure. They develop fatty liver. Their triglycerides drift up. Their HDL drifts down. They start to feel tired in the afternoons. They develop sugar cravings. They sleep worse. Eventually, the beta cells start to fail under the chronic demand, insulin production declines, glucose finally starts to climb — and only then, after two decades of damage, do the standard tests pick up the disease.
By the time someone is officially “pre-diabetic,” the disease is not new. It is old. The patient simply has new evidence of it.
The test almost no one orders
Fasting insulin is a simple blood test. It costs roughly $30 cash pay at LabCorp or Quest. It requires nothing more than an 8-12 hour fast. It can be ordered on the same draw as a standard lipid panel. It is the single most informative metabolic test available to most adults — and it is almost never on the standard workup.
The reference ranges from a functional medicine perspective:
- Under 5 µIU/mL — Optimal. Highly insulin sensitive.
- 5 to 10 µIU/mL — Healthy.
- 10 to 15 µIU/mL — Borderline. Insulin resistance developing.
- Above 15 µIU/mL — Hyperinsulinemia. Decade-plus warning of type 2 diabetes.
A 2023 study of 1,313 young adults aged 16 to 25 in India looked specifically at the gap between insulin and glucose. Among the participants with normal HbA1c (under 5.7%), more than ten percent had fasting insulin above 15 mIU/L. Their standard diabetes screening came back perfectly clean. Their pancreases were working at twice the normal output to keep that screening clean. And nobody told them.
A separate review of fasting insulin testing in clinical practice noted: “We routinely see patients with fasting insulin levels of 15 to 20 µIU/mL who have been told their labs are ‘normal.’ From a functional medicine standpoint, these individuals are already on a trajectory toward metabolic disease that is fully reversible with early intervention. Identifying elevated fasting insulin early — often 10 to 20 years before a Type 2 diabetes diagnosis — is one of the highest-value clinical interventions we provide.”
If you are over 35 and have not had a fasting insulin tested, you do not actually know whether you are metabolically healthy. You know whether your pancreas is still keeping up. Those are not the same thing.
The pediatric epidemic
If type 2 diabetes were primarily genetic, the prevalence rate in any given population would be relatively stable over generations. Genes do not change in 30 years. Lifestyles do.
In 1990, type 2 diabetes in children was so rare it was barely a clinical category. Most pediatricians could complete their entire careers without seeing a case. The medical literature on pediatric T2D was sparse. The disease was understood to be an adult condition, primarily affecting people in their 50s and 60s after decades of metabolic drift.
In 2025, type 2 diabetes is the fastest-growing chronic disease in American children. Thousands of new pediatric cases are diagnosed each year. The disease in children is more aggressive than in adults — faster beta cell decline, earlier complications, worse long-term prognosis. The drivers are not mysterious. They are sugar-sweetened beverages, ultra-processed foods, sedentary lifestyles, and the constant snacking pattern that keeps insulin elevated all day long.
The genetic pool of American children has not changed since 1990. The food supply, the activity patterns, and the screen-time exposure have changed completely. The disease is environmental, and the fact that we are now diagnosing it in eight-year-olds is the most definitive proof of that fact we will ever get.
This matters for adults too. If T2D were genetic, “it runs in my family” would be a reasonable explanation for getting it. But T2D rates have tripled in the US in 30 years. Same gene pool. Different exposures. The disease is something you do to your metabolism over decades — and something you can stop doing.
The “skinny diabetic” — when BMI lies
One of the more persistent objections to the metabolic disease framework is some version of “but I’m not overweight.” The data complicates that defense.
A meaningful percentage of people with full type 2 diabetes have a BMI under 25. The phenotype is called TOFI — Thin Outside, Fat Inside. These individuals carry their excess fat viscerally rather than subcutaneously. They have normal-looking bodies and dysfunctional livers and pancreases. The visceral fat is metabolically active in a way that subcutaneous fat is not — it pumps inflammatory cytokines directly into portal circulation, drives hepatic insulin resistance, and seeds the cycle of metabolic decline despite a “normal” weight.
Roy Taylor’s research group at Newcastle University has specifically tested this. Their ReTUNE study took normal-BMI type 2 diabetics — BMI of 21 to 27 — and put them through the same dietary intervention used in the larger DiRECT trial. The result: “the study’s MRI scans demonstrated significant reductions in liver and pancreatic fat levels, indicating improved organ function. Notably, the fat content in the liver dropped from 4.1% to 1.4%, aligning with healthy control levels, while pancreas fat reduced from 5.8% to 4.3%.”
Even people with completely “normal” body composition can have excess fat in the wrong organs driving full-blown type 2 diabetes. Remove the ectopic fat, the disease resolves. The variable is not scale weight. It is something called the personal fat threshold — the maximum amount of fat your subcutaneous tissue can safely store before it starts depositing into your liver, your pancreas, and your other organs. The threshold varies enormously by individual, and BMI doesn’t capture it at all. A better screening metric is waist-to-height ratio — your waist measurement at the navel should be less than half your height. Above that, you may be exceeding your personal threshold regardless of what the scale or BMI chart says. The best metric of all is the metabolic panel itself — fasting insulin, trig/HDL ratio, hsCRP, HbA1c, and ApoB. The blood work tells you whether the disease is actually present, regardless of body composition.
If your fasting insulin is elevated and your BMI is “normal,” you are not in the clear. You are in the most under-diagnosed category of metabolic disease in modern medicine.
What’s actually happening while no one is watching
This is the part that should generate urgency in anyone reading this. The hyperinsulinemia phase — the decade or two before official “pre-diabetes” — is not a benign waiting room. It is when the damage accumulates.
By the time someone is officially diagnosed with type 2 diabetes:
- Microvascular damage has already begun. Up to 20% of newly diagnosed type 2 diabetics already have detectable diabetic retinopathy on their first eye exam. The damage to the small blood vessels in the retina started years before the diagnosis.
- Peripheral neuropathy is often already developing. The numbness and tingling in the feet that some patients report at diagnosis is the result of years of metabolic damage to peripheral nerves.
- Kidney filtration may already be declining. The glomerular damage that leads to diabetic kidney disease starts during the hyperinsulinemia phase, not after diagnosis.
- Cardiovascular plaque is well underway. Patients with type 2 diabetes have two to four times the cardiovascular mortality of patients without it — and most of that plaque formation occurred during the silent insulin resistance years that preceded diagnosis.
- Liver fat is established. Most type 2 diabetics have non-alcoholic fatty liver disease (now reclassified as MASLD — metabolic dysfunction-associated steatotic liver disease) by the time they’re diagnosed. The liver fat drives the disease, but the disease also worsens the liver fat. Cycle reinforces itself.
These are not theoretical risks. They are mechanical inevitabilities of letting hyperinsulinemia run unchecked for a decade or two. The fact that your standard glucose tests stayed normal during that period was not protection. It was the absence of detection.
Type 3 Diabetes: when insulin resistance reaches the brain
The newest and most consequential extension of this research is the recognition that what happens in the pancreas and liver also happens in the brain.
The framework is called Type 3 Diabetes — a clinical hypothesis that Alzheimer’s disease is, at the cellular level, a brain-specific insulin resistance disorder. The proposal originated with researchers at Brown University and the University of Pennsylvania. Subsequent work in human brain tissue, animal models, and human longitudinal cohorts has built increasingly convincing evidence for it.
The mechanism, as described in the research: “When someone has insulin resistance, the pancreas continues to try to regulate blood sugar, producing more insulin. These higher levels of insulin in the bloodstream can ultimately reach the brain. The enzyme that breaks down insulin in the brain also breaks down the amyloid proteins in the brain. These proteins can develop into the plaques involved in Alzheimer’s disease. When insulin levels are high, less of the amyloid proteins are broken down, which leads to more plaque buildup. In many instances, this buildup begins two decades before changes in memory and thinking.”
Read that again. Two decades before changes in memory and thinking. The same hyperinsulinemia timeline that drives type 2 diabetes drives Alzheimer’s disease — through a mechanism involving the enzyme that’s supposed to clear both insulin and amyloid plaques from the brain. Chronic high insulin saturates that enzyme. The plaques accumulate. The brain starts to fail decades later.
Type 2 diabetics have significantly elevated rates of dementia and Alzheimer’s. The connection is not coincidental. It is a single disease — metabolic dysfunction driven by chronic insulin resistance — expressing in different organ systems depending on individual susceptibility. The patient who develops T2D and the patient who develops Alzheimer’s may be experiencing the same underlying pathology with different end-organ targets.
The implication, which is profound: catching insulin resistance in the hyperinsulinemia phase doesn’t just prevent type 2 diabetes. It plausibly prevents Alzheimer’s disease as well.
The reframe
If you take only one thing from this post, take this:
The disease your doctor is screening for is the late-stage manifestation of a metabolic process that has been running silently for fifteen to twenty years. The tests they’re using catch it at year eighteen. The test that would have caught it at year three — fasting insulin — costs $30 and is almost never ordered.
By the time you have officially “pre-diabetic” lab values, microvascular damage has started, neuropathy may be developing, your liver is fatty, your cardiovascular system has been under attack, and amyloid plaques may already be accumulating in your brain.
This is the cost of a screening protocol built around the wrong markers. And it is — for most people — completely, mechanically reversible. The disease has not yet become structural. The pancreas can still recover. The liver can still empty. The brain damage can still be limited. But none of that happens unless someone tells you what’s actually going on.
That’s what this series is about.
What’s coming next
The next post pulls back to the mechanism. What is actually causing all of this? What’s the fundamental process driving the hyperinsulinemia, the ectopic fat accumulation, the beta cell stress, the brain inflammation? The answer is the most under-discussed piece of physiology in modern medicine — and it has been documented through MRI imaging studies across multiple research groups since 2008. The medical establishment has known about it for nearly twenty years. They just haven’t built the patient conversation around it.
The Twin Cycle Hypothesis is next.
This post is part of a four-part series on type 2 diabetes — what causes it, what your doctor isn’t telling you, what the drugs can and can’t do, and what actually reverses the disease.
- Pre-Diabetes Is Not the Early Stage of Type 2 Diabetes. It’s the Late Stage of Insulin Resistance. (this post)
- The Twin Cycle: What Actually Causes Type 2 Diabetes
- The ACCORD Trial and the GLP-1 Trap: Why the Drugs Aren’t the Answer
- The Cure: How Type 2 Diabetes Is Reversed
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