Here is a conversation that plays out thousands of times a day across the country. A patient sits down for their annual physical. The bloodwork comes back. HbA1c is 5.6. The doctor glances at it and says, “You’re not pre-diabetic, you’re fine, just keep eating well and exercising.” The patient leaves reassured. Five years later, they are 25 pounds heavier, exhausted, libido is gone, and the same doctor is now writing a metformin prescription.
Nothing in that timeline was inevitable. The 5.6 was a warning, not a pass. The system that called it normal is calibrated to flag established disease, not to catch the metabolic dysfunction that drives most of midlife’s hormone problems.
What the Cutoffs Actually Mean
The American Diabetes Association defines pre-diabetes as an HbA1c between 5.7 and 6.4 and diabetes as 6.5 or higher. These cutoffs are not random. They are statistical thresholds drawn from large population studies, designed to identify people whose blood sugar dysfunction is severe enough to predict future cardiovascular and microvascular disease at meaningful rates.
The thresholds exist for a reason, and they do their job. The problem is what they were not designed to do. They were not designed to identify the metabolic dysfunction that has been brewing for a decade before HbA1c crosses 5.7. That earlier dysfunction does not have a clean diagnostic label. It also happens to be where most of the hormone disruption, weight gain, and energy collapse in midlife actually starts.
So a 5.6 is technically “not pre-diabetic.” It is also not normal in the way that a 5.0 is normal. It sits in a zone that the screening system is built to ignore.
HbA1c Is a Lagging Indicator
HbA1c measures the percentage of hemoglobin in your red blood cells that has been glycated, meaning that glucose has bonded to it. Because red blood cells live about 90 to 120 days, HbA1c gives a rolling three-month average of blood sugar.
This is useful for monitoring established diabetes. It is much less useful for catching insulin resistance early. The reason is that insulin resistance can be present for years while HbA1c stays normal. Here is what happens.
The body senses cells becoming less responsive to insulin. To compensate, the pancreas produces more insulin. The extra insulin keeps blood sugar in the normal range. The patient’s HbA1c stays at 5.4 or 5.5 for years while their fasting insulin is climbing steadily. Eventually the pancreas can no longer compensate, and HbA1c starts to rise. By the time it crosses 5.7, the metabolic damage and the hormonal disruption have been accumulating for a long time.
What this means in practice: HbA1c shows you where your body has already lost the fight. It does not show you where the fight started.
The Test Almost No One Orders: Fasting Insulin
Fasting insulin catches insulin resistance years earlier than HbA1c. It is a simple blood test. It costs about the same as any other lab. It is rarely ordered in primary care because it is not part of standard screening guidelines.
A fasting insulin in the single digits (under 10 microIU/mL) is reassuring. A level above 10 with a normal glucose suggests early insulin resistance. A level above 15 is a clear signal that the pancreas is working hard to keep glucose normal and the system is under strain.
Combined with fasting glucose, you can calculate HOMA-IR (Homeostatic Model Assessment for Insulin Resistance):
HOMA-IR = (fasting insulin x fasting glucose) / 405
The cutoff that mainstream medicine uses for “insulin resistance” is around 2.5. The cutoff that optimization-focused practitioners use is closer to 1.5. A patient with a HOMA-IR of 2.0 has clear early insulin resistance even though no one would call them pre-diabetic.
This single calculation, drawn from two cheap blood tests, catches metabolic dysfunction roughly a decade earlier than HbA1c does. It is not part of standard panels because the entire screening system is built around catching disease, not catching the runway to disease.
The Hormone Consequences of Insulin Resistance
This is where the conversation usually stops in a metabolic health post. But for the patient who walked into the office complaining about fatigue, weight gain, low libido, and brain fog, the metabolic story is only useful if it explains the symptoms. It does, and the connection runs through several hormone pathways.
Insulin resistance suppresses SHBG. Sex hormone binding globulin is produced by the liver, and insulin signaling regulates that production. When insulin is chronically elevated, SHBG drops. The downstream effect is different in men and women but problematic in both.
In men, low SHBG combined with stable total testosterone production usually means free testosterone holds up at first, but a larger fraction is being aromatized to estradiol. Total testosterone might still look “normal,” but the patient is symptomatic with rising estrogen relative to testosterone. They feel softer, fatter, less driven, and they cannot understand why because their testosterone level is in range. We discussed the SHBG and free testosterone interaction in the post on hormone labs most doctors skip.
In women, low SHBG raises free testosterone, which in patients with PCOS-pattern physiology contributes to acne, hair thinning, abdominal weight gain, and irregular cycles. It also disrupts the estrogen-to-progesterone balance during the cycle, which contributes to mood changes, sleep disruption, and heavier or more painful periods.
Insulin resistance suppresses progesterone. The luteal phase of the menstrual cycle requires healthy progesterone production from the corpus luteum. Insulin resistance interferes with this through multiple mechanisms, contributing to the anxiety, sleep loss, and PMS-like symptoms that women experience even before they are technically in perimenopause.
Insulin resistance increases aromatization. The aromatase enzyme converts testosterone to estradiol, and aromatase activity is upregulated by visceral fat (which insulin resistance promotes) and by the inflammatory state that comes with metabolic dysfunction. The net effect in middle-aged men is the slow conversion of testosterone they need into estrogen they do not. This is part of why men in their 40s and 50s see body composition shift toward a more feminized pattern even on stable testosterone production.
Insulin resistance impairs thyroid conversion. Chronic high insulin contributes to inflammation, and inflammation impairs the conversion of T4 to active T3. So a patient with insulin resistance often has a normal TSH and a low-normal free T3 with mild functional hypothyroidism on top of the metabolic problem.
The picture that emerges is not five separate problems. It is one upstream driver (impaired insulin signaling) producing five different symptom patterns at once. Treating any one of those patterns without addressing the insulin signaling problem produces partial, temporary results.
Why GLP-1 Medications Work on More Than Weight
This is the mechanism behind why GLP-1 medications like semaglutide and tirzepatide produce broader benefits than weight loss alone. These drugs improve insulin signaling at multiple points: they stimulate insulin release in response to glucose more efficiently, they slow gastric emptying so glucose enters the bloodstream more gradually, and they reduce appetite and food intake, which lowers the insulin load.
The weight loss is the visible result. Patients who lose weight on these medications often report improvements in libido, energy, mood, sleep, and menstrual regularity that go beyond what the weight loss alone would predict. The mechanism is the underlying insulin signaling improvement. We covered the differences between the GLP-1 options in detail under the comparison of semaglutide, tirzepatide, and retatrutide.
This is also why the weight loss alone is not the whole goal. Some patients can address insulin resistance without medication through aggressive lifestyle changes. Others benefit from a structured medical weight management program that combines pharmacology with the metabolic support to use the medication well. Either way, the target is the same: insulin signaling, not just the number on the scale.
What an Optimization-Focused Metabolic Workup Includes
If your last physical reported HbA1c at 5.4, 5.5, or 5.6 and you walked out reassured, the conversation was incomplete. A real metabolic workup includes:
Fasting glucose and fasting insulin (run together so HOMA-IR can be calculated). HbA1c for the rolling average context. A full lipid panel including apoB and Lp(a), not just total cholesterol and LDL. Triglyceride to HDL ratio (a useful insulin resistance proxy). Liver enzymes, since fatty liver is the most common consequence of metabolic dysfunction in this demographic. Inflammatory markers including hs-CRP. Uric acid, which tracks loosely with metabolic dysfunction. Vitamin D and ferritin, which both interact with metabolic and hormone health.
Combined with the hormone panel, this picture lets a clinician see whether your symptoms are driven by the hormone side, the metabolic side, or (most often) both feeding each other.
A 5.6 HbA1c is not a problem you have to live with. It is a signal that the metabolic runway is shortening. Caught now, the trajectory is fully reversible. Caught at 6.4, the work is harder.
If your bloodwork has been called “fine” for years while you have felt anything but, the metabolic picture is one of the first places to look. Schedule a metabolic and hormone workup and we will run the panel that catches the dysfunction your annual physical was not built to find.
