Insulin Resistance — How to Know If You Have It and What to Do About It

Insulin resistance is the most common metabolic condition you have probably never had explained to you in clinical terms. It affects an estimated 40 percent of American adults. It is a primary driver of type 2 diabetes, cardiovascular disease, non-alcoholic fatty liver disease, polycystic ovarian syndrome, and the kind of mid-life weight gain that does not respond to standard interventions. It is also one of the most underdiagnosed conditions in primary care because standard metabolic panels frequently miss it until it has been present for years.

Understanding insulin resistance is foundational to understanding why medical weight loss works differently than caloric restriction alone — and why GLP-1 medications produce the results they do.

What insulin resistance actually is

Insulin is a peptide hormone secreted by the pancreatic beta cells in response to rising blood glucose. Its primary function is to facilitate glucose uptake into cells — particularly muscle, liver, and adipose tissue — by binding to insulin receptors and triggering intracellular glucose transport.

Insulin resistance is a state in which cells fail to respond normally to insulin's signal. The receptor may be present, but the downstream signaling cascade — the sequence of molecular events that translates receptor binding into glucose uptake — is impaired.

The pancreas compensates by producing more insulin. Blood glucose remains controlled — sometimes for years — while fasting insulin climbs progressively higher. This is the critical period: the patient has normal glucose, normal HbA1c, and markedly elevated fasting insulin. Standard metabolic panels miss this entirely unless fasting insulin is specifically ordered.

Why it develops

Insulin resistance is not a single-mechanism condition. Several converging factors drive it:

Visceral adiposity. Visceral fat — the fat surrounding the abdominal organs — is metabolically active. It produces free fatty acids and inflammatory cytokines that directly impair insulin receptor signaling. The accumulation of visceral fat and the development of insulin resistance are bidirectionally related: insulin resistance promotes visceral fat deposition, and visceral fat worsens insulin resistance.

Physical inactivity. Skeletal muscle is the primary site of insulin-mediated glucose disposal. Reduced muscle mass and reduced muscle use (sedentary behavior) diminish the metabolic sink for glucose, increasing the demand on insulin signaling.

Chronic sleep deprivation. Even a single night of disrupted sleep produces measurable insulin resistance the following day. Chronic sleep disruption produces sustained impairment. The mechanism involves cortisol, growth hormone, and direct effects on insulin receptor expression.

Cortisol excess. Cortisol stimulates gluconeogenesis (glucose production by the liver) and antagonizes insulin's action at the receptor level. Chronic stress — producing chronically elevated cortisol — directly drives insulin resistance.

Hormonal decline. Testosterone in both men and women maintains insulin sensitivity through multiple mechanisms. Its decline in mid-life contributes directly to insulin resistance. Estrogen decline in women has similar effects on glucose metabolism. Thyroid dysfunction impairs insulin-mediated glucose uptake independently.

How it produces the symptoms it does

Chronically elevated insulin is the primary signal for fat storage — and specifically for visceral fat storage. This is why insulin-resistant individuals gain weight in the midsection specifically, why they struggle to lose weight despite caloric restriction (their elevated insulin maintains fat storage signaling even in a caloric deficit), and why they experience the energy instability that comes from impaired cellular glucose utilization.

The neurological effects of insulin resistance are increasingly recognized. The brain is an insulin-sensitive organ. Impaired insulin signaling in neurons contributes to the cognitive changes — brain fog, memory difficulty, processing slowness — that many insulin-resistant patients experience.

Elevated insulin also suppresses SHBG production in the liver, which reduces free testosterone — adding hormonal deficiency to the metabolic dysfunction.

How to identify it on labs

Fasting insulin is the most direct measure and the most consistently omitted from standard metabolic panels. A fasting insulin above 10 mIU/L in the context of normal fasting glucose warrants clinical attention. Above 15 mIU/L is clearly elevated. Reference ranges vary by lab, but optimal fasting insulin is generally considered to be under 7 to 8 mIU/L.

HOMA-IR (Homeostatic Model Assessment of Insulin Resistance) is calculated from fasting glucose and fasting insulin: (glucose × insulin) / 405. A HOMA-IR above 1.9 is considered insulin resistant; above 2.9 is significantly elevated.

Triglycerides and HDL. A triglyceride-to-HDL ratio above 2.0 is a reliable clinical proxy for insulin resistance and metabolic syndrome. Elevated triglycerides and low HDL are consistent metabolic signatures of insulin-resistant states.

Fasting glucose. Impaired fasting glucose (100 to 125 mg/dL) indicates pre-diabetes — a late manifestation of insulin resistance that has been present for years. Normal fasting glucose (under 100) does not exclude insulin resistance.

What makes it worse

Alcohol, refined carbohydrates, and ultra-processed foods directly spike insulin and worsen insulin resistance over time. Sedentary behavior, sleep deprivation, and chronic stress are modifiable drivers. Weight gain — particularly visceral fat accumulation — is both a consequence and a cause of worsening insulin resistance.

Some medications — particularly certain antidepressants, antipsychotics, and corticosteroids — induce or worsen insulin resistance. This is worth reviewing in the clinical history.

What actually addresses it

Resistance training is the single most effective lifestyle intervention for insulin resistance. Muscle tissue is the primary site of insulin-mediated glucose disposal — building and maintaining lean mass directly improves insulin sensitivity. Even a single resistance training session produces improved insulin sensitivity that persists for 24 to 48 hours.

Dietary composition. Reducing refined carbohydrate intake, particularly ultra-processed foods with high glycemic loads, reduces the insulin secretory demand on the pancreas. Time-restricted eating and lower-carbohydrate approaches have consistent evidence for improving fasting insulin.

GLP-1 receptor agonists. GLP-1 therapy improves insulin sensitivity through multiple mechanisms — slowed gastric emptying reduces postprandial glucose spikes, improved beta cell function reduces compensatory insulin secretion, and weight loss (particularly visceral fat reduction) removes a primary driver of insulin resistance.

Hormonal optimization. Testosterone restoration in testosterone-deficient men and women directly improves insulin sensitivity. Thyroid correction in hypothyroid patients improves glucose metabolism. These are not optional additions to a metabolic program — they are components of a complete approach.

TW

Travis Woodley

MSN, RN, CRNP — Platinum Biote Provider — Founder, Revitalize

Travis spent 17+ years in high-acuity clinical medicine — emergency, cardiac ICU, and cath lab — before founding Revitalize. He is a Certified Platinum Biote hormone therapy provider, the published author of You're Not Broken — You're Unbalanced, and the founder of the Rebuild Metabolic Health Institute. His clinical writing reflects the same precision he brought to critical care: specific, honest, and built around what actually works.

About Travis →More articles →Rebuild Institute →