"My blood sugar is fine. Why would you check my insulin?"
Because your blood sugar can look fine for years while your body works harder and harder to keep it there. Fasting insulin is one of the ways we see that work happening.
It's one of the labs I find most useful, and many people have never had it checked. Let's talk about what it is and why it matters.
Quick summary: what you need to know
- Fasting insulin measures how much insulin is in your blood after you haven't eaten for several hours.
- It can rise years before blood sugar does. Normal glucose doesn't rule out a problem.
- High insulin makes weight harder to lose. Insulin tells your body to store fat.
- It isn't part of routine screening. Glucose and A1C are the standard tests, and insulin is checked less often.
- One number is one piece. We read it alongside your symptoms, history, and other labs.
What is fasting insulin?
Fasting insulin is a blood test that measures your insulin level after an overnight fast. Insulin is the hormone that moves sugar from your blood into your cells. When your cells stop responding to it well, your body makes more and more insulin to keep your blood sugar normal.
So a fasting insulin level can show how hard your body is working behind the scenes, before your blood sugar ever looks abnormal.
Why can my blood sugar be normal if my insulin is high?
Your blood sugar can be normal while your insulin is high because your body is compensating. Insulin is a message telling your cells to take in the sugar that's in your blood. As your cells stop listening as well, your pancreas has to talk louder. Eventually, it's shouting, and your insulin levels are really high.
Blood sugar only tells us whether the message got through. Fasting insulin tells us how loud the shouting is. If nothing changes, even shouting stops being enough, and that's when blood sugar starts to rise. Read more about insulin resistance in men and women.
Why does fasting insulin matter for weight?
Fasting insulin matters for weight because insulin tells your body to store fat. When it stays high around the clock, losing weight gets much harder, and for people on a narrow balance beam, it can feel nearly impossible.
That's one reason people can do everything right and still not lose weight. It's also one reason we check it when someone tells me nothing is working.
What is a good fasting insulin level?
I don't have one standard number in mind, and labs use different ranges. I almost always want to see it in the single digits. The differences that matter can be smaller than you'd expect. For example, one person with a fasting insulin of 6 and another with 10 may both be told they're in range, and they can feel and respond very differently.
So I never read the number by itself. I want to see your insulin alongside your blood sugar, A1C, body composition, family history, and how you're feeling. If you've been told your labs are fine and you still don't feel well, read why normal labs may not tell the whole story.
Why doesn't every doctor check fasting insulin?
Fasting insulin isn't part of routine screening. The standard tests for diabetes and prediabetes are blood sugar and A1C, and those are what most checkups include. Insulin testing also isn't standardized from one lab to the next, and there isn't one agreed-upon cutoff, so it's harder to use as a screening test.
That makes sense for screening large groups of people. At AgeWell, a physician-led midlife medicine practice for men and women in Amarillo, Texas, we're looking for patterns earlier and in more detail, so fasting insulin is part of how we look at metabolic health. We work alongside your primary care doctor, and this is one place we can add to the picture.
How do I get my fasting insulin checked?
You can ask your clinician whether a fasting insulin test makes sense for you. You'll need to fast before the blood draw, usually overnight, and some medications and supplements can affect the result, so ask what to do before your test.
Fasting insulin is part of every Foundational Assessment, along with a body composition scan and an unhurried conversation about what your numbers mean.
What can lower fasting insulin?
Fasting insulin often responds well to change:
- Eat protein first, with vegetables, and be intentional with sugar and refined carbs.
- Eat meals, not snacks, unless you have a real reason to snack.
- Walk after meals, even for ten minutes.
- Lift weights, because muscle helps use up blood sugar.
- Sleep and manage stress, since both affect insulin.
Sometimes medication is part of the plan too. See our approach to metabolic health.
Frequently asked questions
Is fasting insulin the same as fasting glucose?
No. Glucose is your blood sugar. Insulin is the hormone that keeps it in range. They tell you different things.
Can I have high insulin without diabetes?
Yes. Insulin often rises years before blood sugar does, which is why it can be a helpful early clue.
What is HOMA-IR?
It's a calculation that uses fasting insulin and fasting glucose together to estimate insulin resistance. It's one more piece of the picture.
Should men and women both have fasting insulin checked?
Yes. Insulin resistance affects men and women, and it often travels with low testosterone and belly fat.
See if AgeWell is right for you
This article is for education and isn't a substitute for personalized medical advice. Talk with your clinician about your own situation. If you have severe or urgent symptoms, seek emergency care.
Sources
- Cleveland Clinic: Insulin Resistance
- Cleveland Clinic: Visceral Fat
