Insulin resistance is a state in which muscle, fat and liver cells respond poorly to insulin, so the pancreas must release more of it to keep blood glucose in the normal range. For years the extra insulin keeps glucose readings normal, which is why the condition stays silent at the stage when it is easiest to reverse. It sits upstream of type 2 diabetes, fatty liver disease and much of the cardiovascular risk that travels with excess weight, and it is a spectrum, not a yes-or-no diagnosis.
What it measures
There is no single routine test. The research standard is the euglycemic hyperinsulinemic clamp: insulin and glucose are infused together, and the glucose needed to hold blood levels steady shows how sensitive the tissues are. It takes hours, so clinics use proxies from a fasting blood draw, covered in more depth in the reference entry for Insulin resistance.
The most common proxy is HOMA-IR, from fasting insulin and glucose in the same sample: insulin in microunits per milliliter times glucose in mmol/L, divided by 22.5, or by 405 when glucose is in mg/dL. Where insulin is not measured, the triglyceride-glucose (TyG) index uses triglycerides and glucose instead. Indirect signs count too: a widening waist, high triglycerides with low HDL cholesterol, fatty liver, and dark velvety skin folds at the neck.
Typical values
Insulin assays are not standardized, so insulin-based results are not directly comparable across labs, and published thresholds differ by population, sex, age and method. Read them as directional, against your own earlier results.
| Measure | What it is | How to read it |
|---|---|---|
| Fasting insulin | Insulin after an overnight fast | Rises early; no universal cut-off, use your lab’s range |
| HOMA-IR | From fasting insulin and glucose | Higher means more resistance; thresholds are population-specific |
| TyG index | From fasting triglycerides and glucose | Used when insulin is not measured; cut-offs vary by cohort |
| Fasting glucose, HbA1c | Routine blood tests | Move late; normal results do not rule resistance out |
Glucose itself does have agreed bands. US diabetes guidelines put a fasting plasma glucose of 100-125 mg/dL (5.6-6.9 mmol/L), an HbA1c of 5.7-6.4 percent, or a two-hour oral glucose tolerance test value of 140-199 mg/dL (7.8-11.0 mmol/L) in the band called Prediabetes. World Health Organization criteria start the impaired fasting glucose band higher, at 110 mg/dL (6.1 mmol/L), so the same result can be labeled differently depending on the guideline.
Why it matters for longevity
It is the mechanism underneath several conditions that shorten healthy life, and the defining feature of Metabolic syndrome. It precedes type 2 diabetes by years, and in observational cohorts it is associated with cardiovascular disease, fatty liver, chronic kidney disease, some cancers and cognitive decline. Those studies cannot prove causation, because it clusters with visceral fat, inactivity and high blood pressure.
What lifts it above a purely observational marker is that intervening works. In randomized prevention trials, people with prediabetes who followed a program of modest weight loss plus regular activity cut progression to type 2 diabetes by roughly half, more effectively than metformin did. That is prevention of disease, not proof of a longer life, but it is among the better-supported levers in preventive medicine.
What changes it
Losing fat is the strongest lever, and visceral and liver fat respond first, so sensitivity often improves before the scale moves much. Exercise works two ways: one session raises glucose uptake for roughly a day, and regular strength training adds muscle, the tissue that clears most glucose. A short walk after meals blunts the post-meal rise. Short sleep lowers sensitivity within a few nights, as does untreated sleep apnea. On the plate: less refined starch, sugary drinks and ultra-processed food, more fiber, legumes and whole grains.
Once glucose drifts, medication becomes a real option, with metformin, GLP-1 receptor agonists and pioglitazone all acting on this pathway; that is a decision for a clinician. Some drivers you cannot change: genetic background, family history, advancing age, pregnancy, and drugs such as glucocorticoids that lower sensitivity as a side effect.
Related reading
- How to Improve Metabolic Health: A Practical Guide
- Which Blood Tests Reflect Aging and How to Read Them
- Heart Health: A Prevention Guide for Longevity
- Metformin and Longevity: A Review of the Evidence
Disclaimer. This article is for information only and does not replace medical advice. Talk to a qualified clinician before changing anything about your health.