The One Blood Marker Almost Nobody Checks — And Why It Matters More Than You Think

You've Been Told Your Labs Are "Normal." Here's What They Might Be Missing.

You get your annual bloodwork back. Fasting glucose: normal. HBA1c: normal. Your doctor gives you the thumbs up and sends you on your way.

Or maybe your numbers have started trending upward, but they're not high enough to be considered prediabetes. You're told, "We'll keep an eye on it."

But what if this is exactly the time to start paying closer attention?

Maybe you're gaining weight around your midsection. You're tired by 3pm every day. Cravings hit hard after lunch. And if you're in perimenopause or menopause, it feels like your body is playing by a completely different set of rules than it used to.

Here's what almost nobody tells you: glucose can stay "normal" for years while insulin is already telling a very different story. Insulin can be an important early marker of metabolic health — and it's one of the least commonly ordered tests in a standard checkup.

Looking at insulin earlier may help us understand what's happening before blood sugar crosses into the prediabetes range — when there's often much more we can do.

Why Insulin Matters — Even When Glucose Looks Normal

Insulin is a hormone produced by the pancreas. One of its primary jobs is to help move glucose from the bloodstream into your cells, where it can be used for energy.

When cells become less responsive to insulin — a state called insulin resistance — the pancreas responds by producing more insulin to try to keep blood glucose within a normal range.

The problem is, this can hide what's happening beneath the surface. Your glucose may still look perfectly normal on routine bloodwork, but it may be taking increasingly higher levels of insulin to keep it there.

Over time, if the body can no longer maintain that balance, glucose may begin to rise.

That's why glucose and HBA1c don't always tell us the whole story. They tell us what's happening with glucose. Insulin can help tell us how hard the body may be working to keep glucose there.

What Higher Insulin May Be Telling Us

Fasting insulin isn't a stand-alone diagnostic test, but an elevated or rising level may be a clue that the body is becoming less efficient at managing glucose.

Insulin is also an important fat-storage hormone. When insulin rises, it signals the body to store available energy and suppresses the breakdown of stored fat. That's a normal process after we eat. But when insulin remains chronically elevated, it can make it harder for the body to access stored fat for energy.

This is one reason insulin resistance and higher insulin levels are often associated with increased abdominal fat and difficulty losing weight — even when someone feels like they're doing many of the "right" things.

Insulin resistance and hyperinsulinemia are also associated with:

• difficulty regulating blood sugar

• fatty liver

• higher cardiometabolic risk

• increased risk of prediabetes and type 2 diabetes

And this becomes especially relevant for women in midlife.

Estrogen helps support the way our cells respond to insulin. As estrogen declines during perimenopause and menopause, insulin receptor activity and the signaling pathways that help insulin do its job can become less effective. In simple terms, the cells may not "hear" insulin's message as efficiently.

The pancreas may then need to release more insulin to move glucose into the cells, contributing to insulin resistance over time.

This helps explain why many women notice changes in belly fat, cravings, energy, and weight during the menopause transition, even when their eating habits haven't dramatically changed.

Menopause doesn't automatically mean insulin resistance, but declining estrogen can remove some of the metabolic protection women had earlier in life.

What I See in Clinical Practice

This is one reason fasting insulin is a number I pay attention to with my clients.

Clients often come to me experiencing:

• stubborn weight or increasing belly fat

• afternoon fatigue

• carbohydrate or sugar cravings

• energy crashes between meals

• feeling hungry again soon after eating

• the sense that they're "doing everything right" but their body isn't responding

Their fasting glucose may still be normal. Their A1c may not meet the criteria for prediabetes. Fasting insulin can provide another piece of the metabolic puzzle.

I don't look at the number in isolation or simply ask whether it falls within the laboratory reference range. I consider it alongside fasting glucose, A1c, triglycerides and HDL, body composition, symptoms, family history, eating and movement patterns, and changes over time.

The goal isn't to chase a perfect insulin number. It's to understand what the number may be telling us about the individual.

Why Isn't Fasting Insulin Routinely Checked?

Fasting insulin isn't generally included in routine metabolic panels and must be ordered separately. There's also no universally accepted cutoff for an "optimal" fasting insulin level, and insulin assays can vary among laboratories.

That's different from fasting glucose and A1c, which have established diagnostic thresholds for prediabetes and diabetes.

Fasting insulin shouldn't replace those tests. But it can add useful context, particularly when someone has metabolic symptoms or risk factors despite glucose numbers that still appear reassuring.

What Metabolic Health Experts Are Saying

Several well-known voices in metabolic health have helped bring more attention to insulin and insulin resistance.

Robert Lustig, MD, has written extensively about insulin and metabolic disease and advocates looking beyond glucose alone when evaluating metabolic health.

Benjamin Bikman, PhD, a metabolic scientist whose research focuses on insulin resistance, studies insulin's broader effects on fat cells, fuel use and metabolic function.

Mark Hyman, MD, frequently discusses fasting insulin as part of a more prevention-focused metabolic assessment and advocates looking for insulin resistance before blood sugar progresses into the diabetic range.

While they don't necessarily agree on every aspect of nutrition or metabolic health, their work reinforces an important idea:

There is more to metabolic health than whether your glucose falls inside the standard reference range.

The Good News: Insulin Sensitivity Can Change

Finding signs of insulin resistance isn't a reason to panic. It's information you can use.

Some of the most effective strategies are also the fundamentals:

Build balanced meals. Include adequate protein, fiber-rich carbohydrates, healthy fats and plenty of non-starchy vegetables.

Build and preserve muscle. Skeletal muscle is a major site for glucose disposal, making resistance training increasingly important as we age.

Move throughout the day. Even walking after meals can support glucose regulation.

Prioritize sleep and stress management. Both can influence glucose regulation, appetite and metabolic health.

Look at your individual patterns. There isn't one perfect diet or carbohydrate target for everyone.

This is where individualized nutrition becomes so valuable. Instead of simply being told to "eat less and exercise more," we can look at what your body is actually telling us — your labs, symptoms, body composition, eating patterns, movement, sleep and stress — and build a plan around your physiology.

The Bottom Line

Normal fasting glucose and HBA1c are good news. But they're not always the whole story.

Blood sugar health isn't only about how much glucose is in your bloodstream. It's also about how hard your body may be working to keep it there.

That's why fasting insulin is one of the markers I consider when evaluating metabolic health in clinical practice.

It doesn't diagnose insulin resistance by itself or replace glucose or A1c. But alongside symptoms, health history, body composition, lifestyle and other laboratory markers, it can provide another valuable piece of the puzzle.

If you've been told your labs are "normal" — or that your numbers are starting to creep up and should simply be watched — it may be worth looking beyond glucose alone.

Sometimes the missing piece isn't another diet.

It's knowing what to look for.

Want to better understand what your labs are telling you?

If your labs have been called “normal” but you’re still dealing with stubborn weight, energy crashes, cravings, or other changes that don’t quite add up, there may be more to the story.

At CCS Nutrition, I look beyond individual lab values to help clients understand how nutrition, blood sugar, insulin, body composition and lifestyle patterns fit together.

Learn more about individualized nutrition counseling at CCS Nutrition.

References

1. Singh B, Saxena A. Surrogate Markers of Insulin Resistance: A Review. World Journal of Diabetes. 2010;1(2):36–47.

2. Thomas DD, Corkey BE, Istfan NW, Apovian CM. Hyperinsulinemia: An Early Indicator of Metabolic Dysfunction. Journal of the Endocrine Society. 2019;3(9):1727–1747.

3. De Paoli M, Zakharia A, Werstuck GH. The Role of Estrogen in Insulin Resistance: A Review of Clinical and Preclinical Data. American Journal of Pathology. 2021;191(9):1490–1498.

4. Abdul-Ghani MA, DeFronzo RA. Insulin Resistance and Hyperinsulinemia: The Egg and the Chicken. Journal of Clinical Endocrinology & Metabolism. 2021;106(4)–e1899.

5. Kim SH, Reaven GM. Insulin Resistance and Hyperinsulinemia: You Can't Have One Without the Other. Diabetes Care. 2008;31(7):1433–1438. doi:10.2337/dc08-0045.