Why Fasting Insulin May Be the Most Important Test You're Not Getting

“You can’t manage what you don’t measure.” — Peter Drucker

Introduction

We often hear about the importance of monitoring blood sugar—but what about the hormone that controls it? Insulin plays a central role in energy storage, fat metabolism, and long-term health. And while glucose is commonly measured during routine lab work, fasting insulin is often left out—despite being a powerful early indicator of insulin resistance.

In fact, by the time glucose levels rise into the prediabetic range, fasting insulin may have been elevated for years (Hyperinsulinemia). That means critical warning signs are missed—until it’s much harder to reverse course.

In this article, we’ll explore what fasting insulin really measures, why it often reveals more than glucose or A1c alone, and how it can help identify problems early—long before a diagnosis of diabetes, obesity, or cardiovascular disease ever appears.

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Fasting insulin is one of the most powerful early indicators of metabolic health—but it’s rarely included in routine blood work. In this episode, we dive into what fasting insulin can reveal about your risk for insulin resistance, diabetes, and other chronic conditions—long before symptoms begin.

Tap play below to learn why this simple test could be the missing link in proactive health and what steps you can take to improve insulin sensitivity today.

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What Is Fasting Insulin?

Insulin is a hormone produced by the pancreas that allows your cells to absorb and use glucose (sugar) from the bloodstream. When you eat carbohydrates, insulin is released to help lower blood sugar by moving glucose into your muscle, fat, and liver cells for storage or energy.

A fasting insulin test measures how much insulin is circulating in your blood after 8 to 12 hours without food. It’s one of the most direct ways to assess how hard your pancreas is working behind the scenes to keep blood sugar in check—even when your glucose levels still appear “normal.”

Most people are familiar with fasting glucose or A1c, but these tests only tell part of the story. By contrast, fasting insulin gives insight into your body’s baseline insulin demand—which often rises years before glucose becomes elevated.

Elevated fasting insulin is one of the earliest signs of insulin resistance, a condition where the body’s cells stop responding to insulin efficiently. As resistance builds, the pancreas pumps out more and more insulin to compensate, leading to chronically high levels. This stage is frequently missed in routine lab work, since most providers don’t test for insulin unless blood sugar is already out of range.

According to the National Institutes of Health (NIH), normal fasting insulin typically ranges from 2–20 μIU/mL, but many integrative and preventive medicine practitioners consider 5–7 μIU/mL to be optimal. Values above 10 may indicate early metabolic dysfunction, even if glucose remains normal.

What Is Fasting Insulin?

Insulin resistance doesn’t happen overnight. It develops slowly—often silently—over months or even years, and it frequently begins while blood sugar levels still appear normal. That’s what makes fasting insulin such a valuable early-warning tool: it detects dysfunction before the glucose “alarm” sounds.

Here’s how it works:

When you eat carbohydrates, your body breaks them down into glucose, which enters the bloodstream. In response, your pancreas releases insulin to help shuttle that glucose into your cells, where it can be used for energy or stored for later. This process works seamlessly—until it doesn’t.

Factors like poor diet, chronic stress, lack of sleep, and inactivity can make your cells less responsive to insulin over time. This is called insulin resistance. When resistance sets in, your pancreas responds by pumping out even more insulin to compensate. Glucose levels may still stay in range, but your insulin levels begin to climb.

This compensation phase can continue for years without obvious symptoms. You may notice:

• Weight gain around the abdomen

• Energy crashes or sugar cravings

• Brain fog or fatigue after meals

But unless you’re testing insulin directly, these red flags can easily go unnoticed. Eventually, the pancreas can’t keep up, glucose begins to rise, and prediabetes or type 2 diabetes is diagnosed.

According to the Journal of Clinical Investigation, insulin resistance precedes the onset of type 2 diabetes by at least a decade—and is closely tied to obesity, hypertension, PCOS, and non-alcoholic fatty liver disease.

That’s why waiting for glucose to rise before intervening misses the chance to act early—when the condition is still reversible.

Why Fasting Glucose and A1c Aren’t Enough?

Most routine lab panels include fasting glucose and hemoglobin A1c (HbA1c)—and while these are helpful, they don’t tell the full story of your metabolic health. In fact, you can have completely normal glucose levels and still be insulin resistant.

Let’s break it down:

Fasting Glucose

This measures the amount of sugar in your blood after 8–12 hours of fasting. While helpful, it only captures a single moment in time. Your body may be keeping glucose in range by producing more insulin—but that dysfunction won’t show up unless you measure insulin directly.

Hemoglobin A1c

A1c reflects your average blood sugar over the past 2–3 months. It’s useful for identifying trends, but it can be misleading in early insulin resistance or if you have certain conditions like anemia or altered red blood cell turnover.

The Problem: Compensation Masks the Risk

During the early stages of insulin resistance, your body compensates by making more insulin. This keeps glucose and A1c looking normal on paper, while underlying dysfunction grows quietly.

According to research in the journal Diabetes Care, by the time A1c reaches the prediabetic range (5.7 -- 6.4%), many patients have already had elevated insulin for years (American Diabetes Association).

The Missed Opportunity

If you’re only measuring glucose and A1c, you’re reacting to problems after they’ve taken root. By contrast, fasting insulin gives you a head start—an opportunity to intervene before irreversible damage occurs.

This is why many preventive and functional medicine providers consider fasting insulin a foundational test, especially for anyone with a family history of diabetes, PCOS, obesity, or cardiovascular risk.

What High Fasting Insulin Really Tells You

Elevated fasting insulin is one of the earliest and most reliable signs that your metabolism is under strain—even if your blood sugar, weight, or A1c are still in the “normal” range.

When fasting insulin levels rise, it means your body is having to work harder to maintain stable blood sugar. This is typically due to insulin resistance, where your cells stop responding to insulin efficiently. As resistance increases, insulin climbs even higher in an attempt to compensate. Over time, this imbalance can quietly fuel a wide range of chronic conditions.

Conditions Linked to High Fasting Insulin:

• Prediabetes and Type 2 Diabetes
  Elevated insulin precedes rising glucose—often by years. Studies show insulin resistance is a predictor of diabetes risk long before other labs reflect a problem (NIH).

• Obesity and Weight Gain
  Insulin is a fat-storing hormone. When it stays high, it signals your body to store energy instead of burning it. This can lead to stubborn weight gain, especially around the abdomen.

• Non-Alcoholic Fatty Liver Disease (NAFLD)
  High insulin levels drive fat accumulation in the liver—even in people who don’t consume alcohol excessively. NAFLD is now one of the most common liver disorders globally.

• Hypertension (High Blood Pressure)
  Insulin affects sodium retention and vascular tone. Chronically elevated levels can contribute to increased blood pressure and vascular stiffness.

• PCOS (Polycystic Ovary Syndrome)
  In women, high insulin plays a central role in PCOS, contributing to irregular cycles, acne, and difficulty losing weight. Fasting insulin testing is often essential in diagnosing and managing PCOS.

• Cognitive Decline and Alzheimer’s Risk
  Some researchers refer to Alzheimer’s disease as “Type 3 diabetes” because of the growing evidence linking insulin resistance to neurodegeneration (Alzheimer’s Association).

Who Should Consider Fasting Insulin Testing?

Fasting insulin testing isn’t just for people with diagnosed diabetes. In fact, some of the best candidates for this test are people whose standard labs still look normal—but whose bodies are quietly signaling early metabolic dysfunction.

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You may want to test your fasting insulin (and calculate HOMA-IR which stands for Homeostatic model assessment for insulin resistance) if you:

• Struggle to lose weight—especially around your midsection

• Feel fatigued after meals or crash in the afternoon

• Have a family history of type 2 diabetes, heart disease, or PCOS

• Have “normal” glucose and A1c, but carry visceral fat

• Have elevated triglycerides, low HDL, or borderline blood pressure

• Are managing hormonal symptoms (like irregular cycles or low libido)

One of the simplest ways to assess metabolic risk in these cases is to measure waist circumference. Unlike BMI, which doesn't distinguish between muscle and fat, waist measurement reflects the amount of visceral fat stored around your internal organs—which is strongly linked to insulin resistance.

According to the National Institutes of Health (NIH), a waist circumference of ≥40 inches in men or ≥35 inches in women is considered a clinical red flag for metabolic syndrome and insulin resistance.

If your waist circumference is increasing, even with stable weight or BMI, that’s a signal worth paying attention to—especially if you're also noticing energy dips, cravings, or creeping blood pressure. In combination with fasting insulin, this simple measurement can help clinicians detect hidden metabolic risk that would otherwise go untreated.

How to Get Tested and What to Expect

Despite its value, fasting insulin is not included in most routine blood panels—you have to ask for it specifically. Fortunately, it’s a simple and inexpensive test that can be ordered by most healthcare providers or through direct-to-consumer lab services.

What You’ll Need:

• Fasting insulin blood test

• Fasting glucose (ideally done at the same time)
  Together, these allow you to calculate your HOMA-IR, a helpful tool for estimating insulin resistance.

You’ll need to fast for 8–12 hours before your blood draw. No food or drinks other than water. Morning draws are ideal.

A HOMA-IR above 2.0 may indicate early insulin resistance, even if glucose and A1c are still within the "normal" range.

Where to Get Tested:

• Ask your primary care provider to order fasting insulin and glucose together (some may not do this unless you ask directly)

• Work with a functional or integrative medicine provider who uses HOMA-IR routinely

• Order labs through a mobile collection service like Quick Lab Mobile, which offers certified in-home testing for convenience

Many patients find that once they see their insulin and glucose together, they finally have an explanation for stubborn weight gain, fatigue, or early signs of metabolic imbalance—even when other labs looked “fine.”

What to Do If Your Insulin Is High

If your fasting insulin or HOMA-IR comes back elevated, don’t panic—this is a chance to act early and reverse the trajectory before it leads to type 2 diabetes or cardiovascular disease. The good news? Insulin resistance is highly modifiable, especially when caught before blood sugar becomes chronically elevated.

Here are the evidence-based strategies that work:

1. Focus on Blood Sugar-Friendly Nutrition

• Minimize ultra-processed foods and refined carbohydrates

• Choose low-glycemic, fiber-rich carbs (like leafy greens, beans, berries, and quinoa)

• Prioritize lean protein and healthy fats to stabilize blood sugar

• Time your carbs wisely—consider limiting intake to earlier in the day or around activity

• Consider moderate carb restriction if insulin resistance is advanced

A 2020 review published in Nutrients confirmed that a whole-food, low-glycemic diet significantly improves insulin sensitivity—even without weight loss (PubMed).

2. Move After Meals

Exercise is one of the most powerful tools to lower insulin levels, even without weight loss.

• Aim for 150–180 minutes of moderate activity per week

• Walking after meals improves post-meal glucose and insulin control

• Include resistance training to build muscle and improve insulin sensitivity long-term

3. Prioritize Restorative Sleep

Sleep deprivation impairs insulin signaling and raises cortisol, which drives cravings, weight gain, and metabolic stress. Aim for:

• 7–9 hours per night

• Consistent sleep/wake times

• Minimal screens and food before bed

4. Manage Stress Effectively

Chronic stress activates the HPA axis and contributes to cortisol-driven insulin resistance. Support recovery with:

• Breathwork or meditation

• Nature walks or gentle movement

• Limiting caffeine if you’re feeling wired but tired

5. Use Targeted Supplements (If Recommended)

These may support metabolic balance alongside—not instead of—lifestyle change:

• Berberine – mimics metformin, improves glucose and insulin sensitivity

• Myo-inositol – especially useful in PCOS

• Magnesium – supports glucose uptake and insulin signaling

• Alpha-lipoic acid – antioxidant that helps improve insulin resistance

Always speak with a healthcare provider before starting supplements, especially if you’re on medications.

Catching elevated fasting insulin is a clinical opportunity—not a diagnosis, but a signal to act. In many cases, reversing insulin resistance is entirely possible with consistent changes in diet, movement, sleep, and stress patterns.

Conclusion

Fasting insulin may not be a routine part of most lab panels, but it should be—because it gives you a crucial glimpse into your metabolic health long before blood sugar ever crosses into dangerous territory. Elevated insulin is one of the earliest—and most modifiable—signs that your body is under stress.

The reason this matters so much goes beyond numbers on a chart. With healthcare costs rising, and many people facing limited or inconsistent insurance coverage, the burden of chronic illness increasingly falls on the individual. Diagnoses like type 2 diabetes, hypertension, and fatty liver disease bring not only emotional and physical stress—but also steep financial strain.

That’s why prevention isn’t just a medical recommendation—it’s a path to protecting your quality of life.

By catching metabolic dysfunction early, through tools like fasting insulin and HOMA-IR, you give yourself the power to act—before medication is needed, before complications develop, and before the cost of care becomes overwhelming.

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