A fasting insulin test is one of the most important and most overlooked tools in metabolic medicine. Your doctor almost certainly checks your HbA1c and fasting glucose — but without measuring fasting insulin at the same time, early insulin resistance can remain completely invisible for years, silently progressing while every standard lab result comes back marked “normal.”
If you’ve ever been told your blood sugar is “fine,” yet your body tells a different story, this article explains why that happens — and why it’s so common.
Two lab values dominate modern metabolic screening:
- Fasting glucose / HbA1c
- And… almost nothing else
Insulin — the hormone actually responsible for regulating blood sugar — is often ignored.
That omission is not trivial.
It changes everything.
“Fasting insulin vs HbA1c” is a better way to spot early insulin resistance, because glucose can stay “normal” while insulin rises to compensate.
HbA1c Tells You Where You’ve Been — Not What It Took to Get There
HbA1c reflects the average blood glucose over roughly 8–12 weeks.
It answers one narrow question:
How much glucose has been circulating in the blood?
What it does not tell you:
- How much insulin was required to keep glucose “normal”
- Whether tissues are becoming resistant
- Whether the system is under compensatory stress
Two people can have the same HbA1c:
- One with healthy insulin sensitivity
- One with chronically elevated insulin working overtime
On paper, they look identical.
Biologically, they are not.
Insulin Is the Workhorse — Glucose Is the Outcome
Blood sugar doesn’t regulate itself.
It is controlled — moment by moment — by insulin signaling across:
- Liver
- Muscle
- Fat tissue
- Brain
When tissues respond normally, small amounts of insulin keep glucose stable.
When tissues become resistant, the pancreas compensates by producing more insulin.
At first, this works.
Glucose stays “normal.”
HbA1c looks fine.
Doctors reassure patients.
But the cost is hidden.
Fasting Insulin Reveals the Cost of Compensation
Fasting insulin answers a different question:
How hard does the body have to work to maintain normal glucose?
Elevated fasting insulin with normal glucose means:
- Insulin resistance is already present
- The pancreas is compensating successfully — for now
- Metabolic flexibility is declining
This is early metabolic dysfunction, not health.
And it often persists for years before glucose rises.
Why Glucose Is a Late Marker
From a systems perspective, rising glucose represents failure of compensation, not the beginning of dysfunction.
Before glucose increases, the body has already:
- Increased insulin secretion
- Shifted energy storage toward fat
- Altered liver metabolism
- Changed hunger, satiety, and energy signaling
By the time HbA1c crosses into “prediabetes,” insulin resistance is usually well-established.
This is why relying on glucose alone delays intervention.
A Common Scenario (You’ve Seen This)
- HbA1c: 5.2%
- Fasting glucose: 92 mg/dL
- Fasting insulin: never measured
The patient is told:
“You’re metabolically fine.”
Yet they experience:
- Fatigue after meals
- Abdominal fat gain
- Brain fog
- Poor sleep
- Difficulty losing weight
The labs weren’t wrong.
They were incomplete.
Why Insulin Is Still Overlooked in Routine Care
There are practical reasons:
- Guidelines focus on diabetes diagnosis, not early dysfunction
- Insulin reference ranges are wide and poorly contextualized
- Time constraints discourage deeper interpretation
But clinically, this creates a blind spot.
Medicine often waits for numbers to break, instead of asking whether the system is under strain.
Insulin Resistance Is a Continuum, Not a Switch
This is crucial.
Insulin resistance is not:
- “present” one day
- “absent” the day before
It develops gradually, influenced by:
- Chronic stress
- Sleep disruption
- Liver fat accumulation
- Inflammatory signaling
- Sedentary behavior
- Nutrient timing and load
Fasting insulin helps locate where on that continuum someone sits.
HbA1c cannot.
This Is Not an Argument Against HbA1c
HbA1c is useful.
It’s just incomplete.
Think of it this way:
- HbA1c tells you the outcome
- Insulin tells you the effort
Good metabolic health means:
normal glucose with low effort
Not normal glucose at any cost.
Putting It Together: A Systems Interpretation
When fasting insulin is elevated but glucose is normal, it signals:
- Early insulin resistance
- Increased cardiometabolic risk
- Higher likelihood of fatty liver development
- Future deterioration if nothing changes
This is the window where intervention is easiest — and most effective.
Where This Fits in a Bigger Picture
Fasting insulin does not stand alone.
It gains meaning when interpreted alongside:
- TG:HDL ratio
- Liver enzymes (ALT, GGT)
- Body fat distribution
- Sleep and circadian patterns
- Post-meal responses
This is why single-marker thinking fails metabolic health.
What to Do If Your HbA1c Is “Normal” but You’re Not
The goal is not to chase perfect numbers.
The goal is to understand:
- whether insulin is rising to compensate
- whether metabolism is resilient or strained
- whether dysfunction is still reversible
That requires context, not reassurance.
This is exactly why I don’t rely on glucose alone when evaluating metabolic health.
Understanding insulin early changes the entire trajectory.
See also Labs are normal but I feel unwell
If you want to understand what your numbers actually mean before acting, you have the option to work with me through a Clinical Metabolic Assessment — focused on interpretation before intervention
People Also Ask
Can HbA1c be normal while insulin is high?
Yes. HbA1c reflects an average glucose outcome. Insulin can rise for years to keep glucose “normal,” especially early in insulin resistance.
Is fasting insulin enough to diagnose insulin resistance?
It’s useful, but best interpreted with context (fasting glucose, TG:HDL, liver markers, waist/visceral fat, sleep, and ideally post-meal response).
Why do doctors focus on HbA1c instead of insulin?
HbA1c is standardized and tied to diagnostic thresholds. Insulin testing is less commonly ordered and often under-interpreted in conventional workflows.
Author bio
Morteza Ariana is a Functional Nutrition Practitioner specializing in insulin resistance, type 2 diabetes, and systems-based metabolic restoration. His work focuses on identifying upstream drivers of metabolic dysfunction — including insulin load, liver–gut axis disruption, circadian misalignment, and micronutrient gaps — rather than masking symptoms.
He works with high-performing professionals through a structured 12-week Metabolic Restoration Blueprint designed to restore metabolic flexibility and long-term resilience.
If this resonates, the next step is clarity.
The Metabolic Restoration Blueprint is a structured 12-week framework designed to correct upstream metabolic drivers — not just manage symptoms.
Scientific References
Fasting insulin may be informative / sometimes earlier than HbA1c for metabolic risk PLOS
Insulin resistance / hyperinsulinemia can predate glucose intolerance and T2D PNAS
HbA1c has meaningful limitations as a diagnostic marker PubMed
Pitfalls/discordance of HbA1c in diagnosis JCEM
Hyperinsulinemia: an early biomarker of metabolic dysfunction PubMed