Fasting Insulin: The Overlooked Test Revealing Silent Compensation

Fasting Insulin: The Overlooked Test Revealing Silent Compensation

by Laurent Glatz – for Athletic Carnivore

Every year, millions of patients leave their blood work with the same reassuring phrase: “Everything is normal.” Blood sugar at 92 mg/dL. Glycated hemoglobin at 5.5%. Triglycerides at 140 mg/dL. Nothing exceeds official thresholds. They schedule a follow-up for the next year.

Then, ten or fifteen years later, the diagnosis arrives: prediabetes, type 2 diabetes, hypertension, fatty liver disease, metabolic syndrome. The surprise is total. How is it possible to “flip” so suddenly?

The answer is simple: the shift was never sudden. It was invisible.

The test that could have revealed this silent drift is called fasting insulin.

Normal Blood Sugar Can Be Deceptive

In most laboratories, the so-called “normal” range for fasting insulin roughly spans from 2.5 to 20 or even 25 µIU/mL. This range is vast. It means a patient with insulin at 22 µIU/mL can still be considered “within normal limits.”

Yet, from a metabolic standpoint, truly optimal fasting insulin usually lies between 2 and 5 µIU/mL. Beyond 6–7 µIU/mL, early signs of insulin resistance often appear. At 10–12 µIU/mL, the phenomenon is usually established. At 15–20 µIU/mL, pancreatic compensation is already significant.

Calling a 20 µIU/mL level “normal” is tantamount to accepting that the body uses four to five times more insulin than a sensitive metabolism to maintain the same blood sugar.

Because blood sugar itself remains stable.

Here lies the trap. Blood glucose is an extremely tightly regulated variable. The body mobilizes all its resources to keep it within a narrow range, generally between 70 and 99 mg/dL fasting. When cells become insulin resistant, the pancreas increases hormone secretion to force glucose entry. Sugar stays normal. Insulin rises.

Year after year, blood sugar may creep from 85 to 90, then 95, then 99 mg/dL. Always “normal.” Meanwhile, insulin can double, triple, sometimes quadruple. This progression is often linear and silent.

Insulin Rises Before Sugar

This phase could be called the lost window. Fifteen to twenty years during which metabolic disease develops undiagnosed.

When blood sugar finally crosses the 100 mg/dL threshold, classified as prediabetes, the system has already been under strain for a long time. When it reaches 126 mg/dL and type 2 diabetes is declared, insulin resistance is longstanding. Complications have begun developing well before the official label.

Moreover, elevated insulin is not just a marker. It is a pathological driver.

Chronic high insulin stimulates renal sodium reabsorption. Blood volume increases, blood pressure rises. It promotes endothelial inflammation, weakening vascular walls. It increases certain coagulation factors, making blood more prone to clotting. It stimulates hepatic lipogenesis, leading to non-alcoholic fatty liver disease. It acts as a mitogenic hormone, encouraging cell proliferation. It impairs brain insulin sensitivity, contributing to metabolic mechanisms of dementia.

In cancer, two phenomena converge: insulin stimulates cell division and chronic inflammation impairs immune surveillance. For cardiovascular disease, it affects blood pressure, endothelium, coagulation, and lipid metabolism. For obesity, it locks access to fat stores while stimulating their accumulation, creating persistent hormonal hunger.

Thus, elevated insulin precedes, accompanies, and accelerates much of modern chronic disease.

So why isn’t it measured systematically?

Hyperinsulinemia: A Driver of Chronic Diseases

Conventional medicine is structured around diagnostic thresholds. It treats declared diseases. As long as a marker doesn’t exceed an official value, it’s considered acceptable. The logic is that of established disease.

Functional medicine, on the other hand, focuses on dynamics. It observes trends, compensations, early adaptations. It seeks to understand why the body must produce three or four times more insulin to maintain the same blood sugar.

In the first approach, a patient with 98 mg/dL glucose and 18 µIU/mL insulin can be reassured. In the second, they are identified as metabolically at risk in the medium term.

The contrast is striking: one waits for system failure; the other tries to intervene before it occurs.

Fasting insulin does not replace the full panel of tests. It is not a standalone diagnosis. But it sheds light on the hidden mechanics behind seemingly normal numbers.

A simple test, often costing just a few dozen euros, could reveal a pathological trajectory ten, fifteen, or twenty years before the official diabetes diagnosis. It could prompt early adjustments in nutrition, physical activity, stress management, and reduce prolonged exposure to chronic hyperinsulinemia.

Why This Test Is Rarely Prescribed

The question isn’t whether blood sugar is important. It is. The question is why we wait for it to drift before acting, when the hormone controlling it drifts long before.

In an era of exploding healthcare costs and metabolic diseases dominating statistics, ignoring the central marker of energy metabolism is less a technical oversight than a perspective choice.

We can keep watching the dashboard when the engine is already smoking. Or we can decide to open the hood before the breakdown occurs.

Fasting insulin makes no noise. It triggers no spectacular alarm. It simply reveals if the body is silently compensating.

And sometimes, that silence costs twenty years.

Go Further

To connect these signals to your personal metabolic terrain, you can start by [taking the free questionnaire](/en/questionnaire-neuroprofil.html). If you want a structured strategy, you can also [receive a personalized 30-day program](/en/rapport-premium.html).

FAQ

Does normal blood sugar exclude insulin resistance?

What is the purpose of fasting insulin testing?

Is high fasting insulin a diagnosis on its own?

Why is this marker interesting in nutrition?

What is the link with the Athletic Carnivore questionnaire?

The real question is not just whether your blood sugar is still normal, but how much insulin your body must produce to maintain that appearance of normality.

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