Why You Should Be Testing Your Fasting Insulin Levels (Not Just Glucose)
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When people think about blood sugar, they usually focus on glucose. They use tests like fasting glucose, A1C, or maybe a continuous glucose monitor (CGM) if they’re ahead of the curve. But there’s another critical piece of the puzzle that’s often overlooked: fasting insulin.
Every test has a particular niche. Fasting glucose gives you a snapshot of your glucose levels. A1C provides a rolling average that is reflective of your glucose control over approximately 3 months. CGMs allow for real-time blood sugar biofeedback. Fasting insulin has a unique place amongst these tests since it can be your early warning system for metabolic dysfunction, before glucose levels go haywire. Unfortunately, fasting insulin is not included in standard bloodwork, you will have to request it from your doctor.
If you want a deeper understanding of your metabolic health, energy levels, and long-term disease risk, fasting insulin deserves a front-row seat.
What Is Fasting Insulin?
Insulin is a hormone secreted by the pancreas that helps shuttle glucose from your bloodstream into your cells, where it can be used for energy or stored for later. After you eat carbohydrates, insulin rises to help manage the increase in blood sugar.
A fasting insulin test measures the amount of insulin circulating in your blood after you’ve fasted (usually 8–12 hours). Ideally, insulin levels should be low when you haven’t eaten since your body doesn’t need to do much blood sugar management in a fasted state.
Why Fasting Insulin Matters (Even If Your Glucose Looks Fine)
Here’s the problem, glucose levels can stay relatively normal for years, even while your insulin levels are skyrocketing behind the scenes.
That’s because your body will work hard to keep blood sugar in check by pumping out more and more insulin to maintain balance. This is where a fasting insulin test is valuable. After fasting blood sugar should be naturally low. However, people with poor metabolic health have been shown to have higher fasting insulin levels than healthy individuals. In this way, fasting insulin can give you a heads up that your body is working harder than it should. A 2018 study published in Cell Metabolism found that hyperinsulinemia (high insulin levels) precedes and predicts insulin resistance and type 2 diabetes by years.
If left unchecked, high fasting insulin levels can lead to insulin resistance, where your cells stop responding to insulin efficiently. Over time, this can evolve into prediabetes, type 2 diabetes, and increase the risk of heart disease and cognitive decline.
What’s a Healthy Fasting Insulin Range?
Just like blood glucose, there is debate as to the “optimal” level of fasting insulin. Insulin varies by age, sex, body composition, and underlying medical conditions. At this time, there are some general guidelines for a healthy fasting insulin range.
- Optimal: 2–6 µIU/mL
- Acceptable: 6–10 µIU/mL
- Elevated/Concerning: >10 µIU/mL
Most labs will flag anything above 25 µIU/mL as abnormal, but by that point, your body may have already been struggling with metabolic dysfunction for an extended period of time.
Please note that fasting insulin blood tests should accompany a fasting blood glucose test. The combination of these can provide a better picture of your metabolic health.
Why Test Fasting Insulin? Here’s What It Can Reveal:
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Early Detection of Insulin Resistance
Fasting insulin picks up signs of insulin resistance and it will likely flag as abnormal before glucose or A1C levels show issues. This makes it a powerful tool for prevention.
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Insight into Fatigue and Energy
Chronically elevated insulin can lead to energy dips, cravings, and fatigue. If you're constantly “hangry” or feel like you’re on a blood sugar rollercoaster, insulin may be to blame. -
Cardiometabolic Risk
Higher fasting insulin is linked to increased risk of cardiovascular disease, even in people with normal glucose and cholesterol.
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More Precise Nutrition and Lifestyle Strategies
Understanding your insulin levels can help personalize your diet, exercise, and supplement choices. For example, someone with elevated fasting insulin might benefit more from more physical activity and lower-carb meals to improve insulin sensitivity.
How to Test Your Fasting Insulin
You can ask your healthcare provider to include it in your next lab panel. It’s a simple blood test, but it is often not included in routine metabolic screenings unless you specifically request it.
You can also use direct-to-consumer lab services, many of which offer fasting insulin testing at home or through local draw centers.
As I mentioned before, fasting insulin is best interpreted when paired with a fasting glucose test. Pair it with fasting glucose and calculate your HOMA-IR score (a basic estimate of insulin resistance).
HOMA-IR = (Fasting insulin µg/mL × Fasting glucose mmol/L) ÷ 22.5
A normal HOMA-IR is typically between 0.5 and 1.4. Values greater than 1.9 are considered early insulin resistance and values greater than or equal to 2.9 indicate insulin resistance.
Bottom Line: Don’t Just Watch the Sugar—Watch the Insulin
Testing fasting insulin gives you a clearer, earlier, and more actionable picture of your metabolic health than glucose alone. Plus, it may help you to be proactive about your health, which is always better than being reactive. Fasting insulin is one of the most underutilized yet powerful markers of metabolic health. Ask for it. Track it. And use it to guide smarter, more personalized health decisions.
And remember, GOOD IDEA is here to help you support healthy blood sugar responses, especially around meals. It's not just about the numbers on your labs; it’s about giving your metabolism the daily support it needs to thrive.
Author: Dr. Colleen Gulick, Ph.D. (ExPhys), MS (ExPhys), BS (BioE), EIT (ME), CSCS