Your Brain Became Insulin Resistant Before Your A1c Noticed

Your A1c is 5.5. Your fasting glucose is 92. Your doctor is pleased.

You, however, need a nap at two in the afternoon. You get shaky and irritable if lunch runs late. You lose your words. You crave something sweet after every meal. Your waist has crept outward despite eating almost nothing different from a decade ago, and you have started to worry about your memory.

Everyone agrees that your blood sugar is normal.

Here is the question I want answered. How much insulin did it take to keep it there?

Blood glucose is a tightly defended number. Your body will sacrifice nearly everything to keep it in range, because too much or too little can be dangerous within hours. So when glucose finally rises, it does not mean the problem just started. It means that your compensation has begun to fail.

For years, sometimes decades, the pancreas may simply produce more insulin to hold the line. The blood sugar stays normal. The lab stays quiet. Meanwhile, the brain is living with the consequences.

A normal glucose can be a success story for your pancreas and a warning sign for everything else.

Insulin Is a Brain Hormone

Most people think of insulin as the hormone that moves sugar into cells. That description is true, and it is badly incomplete.

Insulin receptors are found throughout the brain, with notable density in the hippocampus, the hypothalamus, and parts of the cortex. These are the regions that handle memory, appetite, and thought. Insulin reaches the brain largely by crossing the blood-brain barrier through a transport process. Inside the brain, insulin signaling appears to support synaptic function, memory formation, and the health of neurons.

That changes the entire picture. Insulin is not only a fuel manager. It is a communication signal to the master system.

Here is a cruel irony. In a person with chronically high insulin, that transport across the blood-brain barrier may decrease. So you can have far too much insulin in your blood and too little signaling in your brain at the same time. The body is flooded, and the brain is short.

The hypothalamus, your appetite and energy thermostat, depends on insulin and leptin to determine how much energy you have stored. When those signals fail to get through, the brain may conclude that you are starving, even when your body holds plenty of reserves. Hunger rises. Metabolism falls. Your cravings are not a moral failure. They are a misread fuel gauge.

Your Brain Runs on a Razor Thin Margin

Your brain consumes about a fifth of your resting energy, and it holds almost no fuel in reserve. Neurons depend on a constant delivery of glucose, or of ketones when glucose is scarce. Glucose enters the brain through specialized transporters, called GLUT1 at the blood-brain barrier and GLUT3 on neurons.

When delivery falters, thinking falters first. This is why a dropping blood sugar can feel like anxiety. Your body responds to falling glucose by releasing adrenaline and cortisol to rescue it. Your heart races. Your hands shake. You feel a sudden surge of dread. Nothing is wrong in the room. Something is wrong in the fuel line.

I have seen people treated for panic attacks that arrive like clockwork around ninety minutes after a high-carbohydrate meal. Medication may quiet the alarm. It does not address why the alarm keeps ringing.

So when I ask about your mood, I also ask what you ate, and when.

Type 3 Diabetes: A Name Worth Examining

You may have encountered the phrase type 3 diabetes, a term some researchers have proposed for the insulin resistance seen in brains affected by Alzheimer disease. It is a provocative idea. It is not an official diagnosis, and it should not be used as though it were.

Here is what we can say with more confidence.

Established evidence shows that type 2 diabetes raises the risk of dementia, and vascular disease is part of that link. Brain imaging has shown reduced glucose use in regions affected by Alzheimer disease, and these changes may appear years before symptoms. Brain tissue studied after death has shown impaired insulin signaling in Alzheimer disease.

There is also a fascinating molecular overlap. An enzyme called insulin-degrading enzyme breaks down insulin, and it also helps break down amyloid beta. A working hypothesis proposes that when insulin is chronically high, this enzyme may be kept busy with insulin and may have less capacity for clearing amyloid. That idea is elegant. It has not been proven as a primary cause in humans.

My clinical takeaway is modest and urgent at once. If metabolic health matters this much to the brain, then we should measure it decades earlier than we typically do. Prevention cannot begin at the memory clinic.

The Labs I Actually Want

If you have only had a fasting glucose and an A1c, you have seen the end of the movie. These are the additional measurements I find helpful.

• Fasting insulin. This one test can reveal compensation long before glucose moves. Laboratory reference ranges are often wide, because they reflect a population in which metabolic dysfunction is common. In my practice, I want to see it comfortably low, and I interpret it in context.

• HOMA-IR, a simple calculation from fasting insulin and glucose that estimates insulin resistance.

• Triglycerides and HDL cholesterol. A high triglyceride to HDL ratio is a useful, inexpensive signal of insulin resistance.

• Oral glucose tolerance testing with insulin measured over time, when the picture is unclear. Some people have normal fasting numbers and striking insulin surges after a meal.

• Fasting glucose and hemoglobin A1c, with one caution: A1c depends on the lifespan of red blood cells, so iron deficiency, anemia, and blood loss can skew it.

• Uric acid, liver enzymes such as ALT, and GGT, which can reflect fatty liver and metabolic stress.

• Continuous glucose monitoring for a few weeks, which can be an enlightening short experiment. Your individual response to oatmeal may differ dramatically from the response of the person beside you.

And alongside these, I measure what is actually on your body. Waist circumference and muscle mass often tell me more than a bathroom scale.

Why Insulin Resistance Happens

Insulin resistance is not primarily a failure of willpower. It is a state in which cells protect themselves from an overload of fuel. Your cells have received more than they can handle, so they turn down the volume.

Many inputs feed that overload, and sugar is only one of them.

• Sleep loss. Even a few nights of poor sleep can measurably reduce insulin sensitivity in healthy adults.

• Chronic stress. Cortisol raises blood sugar by design, in order to fuel a fight that never comes.

• Muscle loss. Skeletal muscle is the largest site of glucose disposal in your body. Less muscle means a smaller storage tank.

• Inactivity. A contracting muscle can pull glucose in through GLUT4 transporters by a route that does not depend on insulin. This is one of the most beautiful facts in all of physiology.

• Toxic burden. Environmental chemicals, including certain persistent pollutants, are associated with metabolic dysfunction, and they are part of what I consider when the bucket is full.

• Chronic inflammation. Inflammatory cytokines can interfere with insulin signaling inside the cell.

• Hormonal transitions. Falling estrogen in perimenopause tends to shift fat toward the abdomen and change insulin sensitivity. Polycystic ovary syndrome is strongly connected to insulin as well.

• Mistimed circadian patterns. Late eating, night shifts, and bright light at night push metabolism out of sync with the clock.

Most diet plans address a single line of this list. That is why they so often work for a while and then stop.

The Liver Saw It First

If you want to know where insulin resistance often begins, look at the liver.

After a meal, insulin tells the liver to stop producing glucose and start storing fuel. The liver stores carbohydrate as glycogen, and that storage tank has a limit. When it is full, the excess can be converted into fat through a process called de novo lipogenesis. Fructose, in large amounts and especially in liquid form, flows into this pathway with little regulation.

Fat then accumulates inside the liver cells. Fatty liver disease now affects an enormous share of adults, including many who are not overweight, and increasingly affects children. A fatty liver grows resistant to insulin, keeps releasing glucose when it should stop, and exports triglycerides into the blood. That is why those high triglycerides show up on your lipid panel, and why a slightly elevated ALT deserves curiosity rather than a shrug.

This is also why fasting glucose often creeps upward in the morning even if you ate nothing overnight. That sugar is not coming from dessert. It is coming from a liver that has stopped listening.

The liver also matters for your hormones and your toxic burden. It is the organ that packages and clears estrogen, and it carries out much of your detoxification chemistry. When it is overloaded with fuel, every downstream system feels the congestion.

Ketones: Your Brain Has a Backup Generator

Your brain is often described as a glucose-only organ. That is not accurate. When insulin falls, during an overnight fast or sustained exercise, the liver produces ketone bodies from fat. Beta-hydroxybutyrate, the most abundant ketone, crosses the blood-brain barrier and can supply a substantial share of the fuel for the brain.

There is evidence that in Alzheimer disease, the brain may struggle with glucose while still taking up ketones relatively well. That has raised real scientific interest in ketogenic strategies for cognition. Results so far are preliminary, and the studies are small.

Beta-hydroxybutyrate is also more than a fuel. It acts as a signaling molecule, and laboratory work suggests that it can influence inflammation and gene expression.

What matters clinically is metabolic flexibility, the ability to move smoothly between burning glucose and burning fat. A metabolically flexible person can miss lunch and feel fine. An inflexible person misses lunch and wants to bite someone. High insulin blocks fat release, so a person with chronically elevated insulin can carry abundant stored energy and be unable to reach it.

That is the deeper meaning of feeling tired after meals and shaky between them. You are locked out of your own pantry.

I do not recommend a strict ketogenic diet for everyone. It is not suitable for many people, including during pregnancy, and it can stress some thyroid, hormonal, and gallbladder situations. The goal is not ketosis as an identity. The goal is flexibility.

How It Can Feel, Decade by Decade

Insulin resistance rarely announces itself. It tends to wear a different costume in each stage of life.

• In your twenties, it may look like acne, irregular cycles, or a difficult conception.

• In your thirties, it may look like stubborn weight after a pregnancy and a mid-afternoon crash that you treat with coffee.

• In your forties, it may look like a thickening waist, poor sleep, rising blood pressure, and word-finding trouble that you blame on perimenopause or a busy life.

• In your fifties, it may look like fatty liver, joint pain, and borderline numbers on every panel.

• In your sixties and beyond, it may look like muscle loss, numbness in the feet, and memory concerns.

One root. Many costumes. A series of specialists may each treat a single costume without ever meeting the actor.

I approach it the other way around. I ask what single upstream pattern could explain this whole timeline, and then I measure it.

Pregnancy, Children, and the Family Inheritance

Metabolic health is a family story. During pregnancy, insulin resistance rises naturally so that fuel can reach the baby. Gestational diabetes reveals when the mother cannot compensate, and it is an important signal for her long-term health that often gets forgotten after delivery. Maternal metabolic health shapes the environment in which the fetal brain develops, and it can influence the metabolic programming of the child through epigenetic mechanisms that are still being mapped.

For children, I watch for the early signs: afternoon meltdowns, a dark velvety patch on the neck or armpits called acanthosis nigricans, abdominal weight, and blood sugar swings that look exactly like behavior problems. A child who falls apart at four in the afternoon may be hungry at a cellular level.

This work is never about shaming a parent or a child. It is about understanding the terrain and tending it together.

The Sequence That Actually Works

I do not begin by handing you a list of forbidden foods. I begin with the leverage points, in order.

First, I protect sleep and the airway, since insulin sensitivity falls quickly without them.

Second, I build meals around protein and fiber. A meaningful amount of protein at breakfast can change the whole day. Eating fiber and protein before starches tends to soften the glucose rise.

Third, I move glucose with muscle. A ten minute walk after meals can noticeably reduce a post-meal spike. Resistance training builds the storage tank.

Fourth, I time the food. Eating more of your calories earlier in the day and leaving a clear overnight fast suits your circadian biology.

Fifth, I address what is feeding the resistance: inflammation, gut dysfunction, hormone transitions, and the toxic burden bucket.

Sixth, I support the brain directly, with a plan to reduce neuroinflammation, increase neurogenesis, and rebalance neurotransmitters. A comprehensive functional neurological exam shows me how those circuits are performing today. When memory is a concern, a NeuroQuant volumetric MRI can give us a baseline of hippocampal volume.

Medications can also have an important role, and that is a conversation for you and your prescribing clinician. Nothing here is a reason to stop one on your own.

Three Questions to Ask at Your Next Appointment

You do not need a new doctor to begin this conversation. You need better questions.

First, ask to see your fasting insulin alongside your fasting glucose. If it has never been measured, ask why not.

Second, ask to compare your triglycerides, HDL, liver enzymes, and blood pressure from five years ago with those of today. A single value may look unremarkable. A slow drift across years can tell a very different story, and nobody tends to look at the slope.

Third, ask how your muscle mass is changing. Most standard visits record your weight and nothing about what that weight is made of. Two people can step on the same scale with entirely different metabolic futures.

Bring your own observations too. Note how you feel two hours after a typical breakfast. Note what happens when a meal runs late. Those are metabolic data points, gathered by the only person who lives in your body every day. They belong in the record alongside the lab values.

The Hopeful Part

The upstream position is the powerful one.

Insulin resistance responds to what you do, often within weeks. Muscle responds. Sleep responds. Inflammation responds. Mitochondria can grow in number and in function. The same brain that has been running on an unreliable fuel line can begin to receive steady signal again.

You are not simply getting older. You may be running a metabolic deficit that nobody measured.

Measure it early. Measure the right thing. Then change the conditions.

Your energy can steady. Your thinking can sharpen. Your brain can receive the signal it has been missing.

Schedule Your Comprehensive Functional Neurological Exam Today

Book your Comprehensive Functional Medicine Eval/Neurological Exam today to discover what the contributing root causes are that are underlying your health concerns.

Begin at drleiladoolittle.com. I see patients by telehealth and in person in Dallas, Texas and Compton, Arkansas.