Fasting Insulin: The Test Your Annual Physical Skips

Marcus, a 52-year-old regional sales director, came to see me last spring with a folder of what he called his "clean bills of health." Five years of annual physicals. Every fasting glucose between 88 and 96. A1c of 5.2, then 5.3, then 5.4 — "still normal," his doctor said each time. Cholesterol fine. Blood pressure fine. Go home, keep doing what you're doing.

But Marcus had gained 30 pounds over those five years. His waistband told a story his labs didn't. He napped in his car between sales calls. He'd read that his father's type 2 diabetes "came out of nowhere" at 58 — and something in him suspected it wasn't nowhere at all.

I ordered one test his physicals had never included: fasting insulin. It came back at 21 µIU/mL — roughly three times where I like to see it. His glucose was normal because his pancreas was pumping out enormous amounts of insulin to keep it that way. He wasn't headed toward insulin resistance. He was standing in the middle of it, five years into the process, and not a single routine lab had said a word.

Here's what I want you to take from his story: glucose is the last domino to fall. Fasting insulin tells you how hard your body is working to keep it standing. And that test costs about the same as a pizza.

Why Your Glucose Can Be "Normal" While You're Getting Sick

Understanding fasting insulin requires understanding the deal your pancreas has made with your metabolism.

Insulin is the hormone that escorts glucose out of your bloodstream and into your muscle, liver, and fat cells. When those cells start ignoring insulin's knock — the condition we call insulin resistance — your pancreas doesn't give up. It shouts. It secretes more and more insulin to force the same amount of glucose into increasingly resistant cells.

For years, sometimes for decades, that strategy works. Your fasting glucose sits at a tidy 90. Your A1c is a comfortable 5.3. On paper, you're fine.

But look at the insulin numbers underneath and you'd see the whole exhausting machinery: insulin climbing from 6 to 9 to 14 to 20 µIU/mL while glucose never budges. This is exactly what the landmark IRAS (Insulin Resistance Atherosclerosis Study) researchers documented — insulin levels rise and stay elevated long before glucose abnormalities appear (1).

Dr. Gerald Reaven described this pattern back in 1988 when he named Syndrome X — what we now call metabolic syndrome. His central insight was uncomfortable and still underappreciated: a person with normal glucose and sky-high insulin is far closer to type 2 diabetes and cardiovascular disease than a person with slightly elevated glucose and low insulin (2). The glucose test rewards your pancreas for running itself into the ground. The insulin test catches it mid-collapse.

This is why, in my practice, I consider isolated glucose screening a form of looking at the smoke and never checking for the fire. If you've read my guide on why "normal" labs can still leave you feeling terrible, this will sound familiar: the marker everyone checks is often not the marker that tells the story.

The hidden timeline

The natural history of type 2 diabetes is not a sudden event. It is a slow-burning compensation with a recognizable sequence:

• Years 1–10: Insulin climbs steadily. Glucose stays perfectly normal. Weight creeps on, mostly around the middle. Energy dips after meals. Nobody checks insulin, so nothing is said.
• Years 10–15: Insulin peaks and starts to falter. Glucose begins drifting up — first the "100–125" prediabetes band, flagged only if your doctor notices.
• Year 15+: The pancreas fatigues. Insulin can no longer compensate. Glucose crosses into the diabetic range, and now — finally — every test in the standard panel lights up.

By the time the standard tests catch the disease, you are two-thirds of the way through a fifteen-year process. Fasting insulin lets you see it in year three, when the fix is diet and walking shoes instead of medications. Research following prediabetic patients shows the same pattern: insulin and it alone identifies progressing patients years before glucose does (3).

What Fasting Insulin Actually Measures — and How to Get It

The test is exactly what it sounds like: a single blood draw, first thing in the morning, after a 10–12 hour fast, measuring the concentration of insulin in your blood. Water and black coffee are typically fine; take nothing else by mouth. If you're already getting a fasting glucose drawn, the insulin draw is the same needle and adds little cost — it's often under $30 out of pocket.

There is nothing exotic about it. The reason it isn't ordered isn't science — it's habit, insurance coding, and guidelines built around glucose endpoints rather than metabolic health. More on that below.

Notice the trap in the middle column: many laboratories flag fasting insulin only above 25 µIU/mL. By that standard, Marcus's 21 was "normal." A reference range built on a population where the majority have some degree of insulin resistance is not a health standard — it's a census.

*These are clinical discussion ranges, not universal treatment thresholds. Interpretation depends on your glucose, medications, body composition, and history — this is exactly the kind of result worth reviewing with a clinician rather than self-diagnosing.*

HOMA-IR: two cheap numbers, one powerful answer

The single fasting insulin value is useful, but insulin makes the most sense in context. Pair it with the fasting glucose from the same draw and you can calculate HOMA-IR — the Homeostatic Model Assessment of Insulin Resistance, first validated in 1985 (4):

> HOMA-IR = (fasting insulin µIU/mL × fasting glucose mg/dL) ÷ 405

For Marcus: 21 × 92 ÷ 405 ≈ 4.8. Under 1.0 suggests excellent sensitivity; 1.0–1.9 is reasonable; 2.0–2.9 signals early resistance; above 2.9 is significant insulin resistance. At 4.8, Marcus's pancreas was working roughly five times harder than it needed to.

I run this same calculation for nearly every new patient in my practice. It takes thirty seconds, and it has reshaped more treatment plans than any other two numbers on the intake labs.

Why Your Doctor Probably Didn't Order It

I want to be fair to conventional medicine here, because the omission isn't laziness — it's the way the system is built.

• Guidelines are anchored to glucose. Screening recommendations from major diabetes organizations key off fasting glucose, A1c, and risk calculators — not insulin. A test that isn't in the guideline flowchart rarely enters the order set.
• Insurance coding follows the guidelines. An insulin level ordered "screening" may not be covered, so clinics skip it rather than create a bill surprise.
• The normal-lab fallacy compounds. If glucose and A1c are normal, the visit is coded as unremarkable. Nobody orders deeper markers when the standard panel says everything is fine — which is precisely the problem I described in my optimal ranges guide.
• Time pressure. A fifteen-minute annual visit has room for the standard panel and little else.

The result is a systemic blind spot: the single most informative early marker of the disease that will affect roughly one in three Americans goes unmeasured in the very visit designed to catch disease early.

The Downstream Cost of High Insulin (It's Not Just Diabetes)

Insulin resistance doesn't wait politely for diabetes to develop before it does damage. Chronic hyperinsulinemia is implicated across a whole roster of conditions your annual physical also doesn't predict:

• Cardiovascular disease. Insulin resistance drives high blood pressure (the kidney retains sodium under insulin's influence), low HDL, high triglycerides, and vascular inflammation. This cluster — not cholesterol alone — is a major reason why heart attacks strike people with "normal cholesterol."
• Weight-loss resistance. High insulin is a storage hormone signal. When it's chronically elevated, the body stays in fat-storage mode and appetite runs hotter. Many patients I treat for "willpower problems" actually have an insulin problem.
• Fatty liver. Non-alcoholic fatty liver disease is both a cause and a consequence of insulin resistance, and it's now estimated in a quarter or more of adults.
• PCOS. In women, elevated insulin drives ovarian androgen production. PCOS and insulin resistance are so tightly linked that insulin testing should be standard in any PCOS evaluation.
• Cognitive decline. Some researchers have called Alzheimer's disease "type 3 diabetes" — the brain's glucose metabolism falters as insulin signaling degrades.
• Erectile dysfunction and low testosterone. Vascular and hormonal damage from insulin resistance shows up in men's health labs years before diabetes. This is a recurring theme in my insulin resistance work.

In other words: fasting insulin is not a "diabetes test." It's a whole-body metabolic health test that happens to also predict diabetes.

What To Do When Fasting Insulin Is High

Here is the genuinely good news: insulin resistance at the fasting-insulin stage is among the most reversible conditions in medicine. Medications exist and sometimes help, but the levers with the deepest evidence are behavioral, and they compound.

1. Restructure your plate — don't just shrink it

Meal composition changes insulin demand faster than calorie counting does. The pattern I use:

• Protein and fiber first. Eating protein and vegetables before starch measurably blunts the glucose and insulin response to the whole meal.
• Cut the naked carbohydrates. Juice, sweetened coffee drinks, white bread, and crackers deliver rapid glucose spikes that demand insulin surges. Swap them for whole-food versions or drop them.
• A sensible eating window. For many patients, compressing meals into a 10–12 hour window gives insulin long overnight stretches to fall. This is a tool, not a religion — and it needs adjusting for medications and history, ideally with a clinician.

2. Lift heavy things

If I could prescribe one intervention for elevated insulin, it would be resistance training. Muscle is your largest glucose sink, and trained muscle pulls in glucose with far less insulin. Two to three full-body sessions per week change insulin sensitivity within weeks — our strength training after 40 guide covers how to start safely. Cardiovascular work and post-meal walks (even ten minutes after dinner) add meaningful glucose disposal on top.

3. Protect sleep like it's a medication

Even a few nights of short sleep measurably reduces insulin sensitivity in healthy volunteers. Sleep apnea is the hidden accelerant here — undiagnosed apnea keeps insulin elevated no matter how well you eat. If you snore, wake unrefreshed, or nap like Marcus did, this deserves evaluation. Our sleep optimization guide covers the fundamentals.

4. Retest on a schedule, not on hope

Insulin responds quickly. In most patients, I recheck fasting insulin and HOMA-IR at 8–12 weeks. A falling trend is the confirmation that the plan is working; a flat trend tells us to look harder — at hidden sugars, alcohol, sleep apnea, thyroid function, or medications like statins' dietary confounders, steroids, or certain antidepressants that can worsen insulin resistance.

5. Consider targeted supplements — tested, not guessed

A small number of compounds have reasonable evidence for supporting insulin sensitivity — berberine being the most studied. But supplements on top of an unchanged diet and a sedentary routine are expensive urine. I use them as accelerants after the foundations, and I retest to confirm they're doing something. My product picks are at the end of this article.

Marcus, by the way, rechecked at twelve weeks: fasting insulin down from 21 to 12, HOMA-IR from 4.8 to 2.6, down eleven pounds without a single meal-replacement shake. His next annual physical will still say "normal glucose" — but now he'll know exactly what that sentence is hiding.

When Insulin Is Normal but You're Still Worried

Fasting insulin isn't the only advanced tool, and a normal result doesn't end the conversation if your story suggests metabolic trouble:

• A1c and glucose trend still matter — the trio of insulin, glucose, and A1c from one morning draw tells the full short-term and long-term story.
• A continuous glucose monitor (CGM) can reveal post-meal spikes and overnight patterns a fasting snapshot misses. I use short CGM trials diagnostically in select patients.
• HbA1c-normal, insulin-high patterns also show up in people with thyroid dysfunction and chronic stress, which is why I interpret metabolic labs alongside the full functional medicine workup.

And the standing caution from every lab article I write: symptoms that are severe, sudden, or progressive — chest pain, unexplained weight loss, marked thirst and urination, fainting — need prompt in-person evaluation regardless of what any screening number says.

The Bottom Line

Your annual physical measures your glucose and calls the metabolic job done. But glucose is the last domino to fall, propped up for years by an insulin level nobody measured. A $30 fasting insulin draw — paired with the glucose you're already getting, yielding HOMA-IR for free — can hand you a fifteen-year head start on the most common chronic disease of our time.

If your labs keep coming back "normal" while your energy, weight, or family history tells you otherwise, ask specifically: "What is my fasting insulin, and what's my HOMA-IR?" If you'd like a physician who orders and interprets labs this way from day one, you can join the practice waitlist or start with one of our interactive health assessments.

Products and Protocols: Test, Don't Guess

Supplements can support insulin sensitivity, but they work as accelerants on top of food, movement, and sleep — never as substitutes. Every product below is something I use in practice, paired with a retest date.

How I choose a supplement

• Match it to a measured target. Berberine for a documented elevated HOMA-IR — not because a commercial told you to "balance your blood sugar."
• Verify the label. Berberine and magnesium are categories where quality varies enormously; use products with third-party testing.
• Give it a decision date. Eight to twelve weeks, then redraw fasting insulin and HOMA-IR. If the numbers didn't move, the product goes.

*Affiliate disclosure: Some product links may earn us a commission at no additional cost to you. Recommendations are based on clinical use, not commissions. Read the full disclosure.*

Do not start berberine, high-dose minerals, or any glucose-affecting supplement without clinician review if you take diabetes medication, insulin, anticoagulants, or have kidney or liver disease — combinations can push glucose dangerously low.