Insulin resistance: definition, how to test for it, and what to do

Definition

Insulin resistance is a metabolic state in which body cells — particularly muscle, fat, and liver cells — respond poorly to the signaling effect of insulin. To maintain normal blood glucose, the pancreas compensates by producing more insulin (hyperinsulinemia).

How it develops

Insulin resistance develops progressively, typically over years:

1. Stage 1: Compensated insulin resistance. Cells start responding less well; pancreas produces more insulin; blood glucose remains normal. No symptoms.
2. Stage 2: Worsening resistance + elevated fasting glucose. Pancreas can mostly compensate, but glucose creeps into “prediabetic” range.
3. Stage 3: β-cell exhaustion. Pancreatic insulin production can no longer keep up; fasting glucose rises into diabetic range. This is type 2 diabetes.

Most people in stages 1-2 don’t know it’s happening because routine medical checkups often don’t include the right tests to catch it early.

What insulin resistance causes

The downstream consequences:

• Weight gain — high circulating insulin promotes fat storage and inhibits fat mobilization
• Visceral fat accumulation specifically (see visceral fat glossary)
• Type 2 diabetes if it progresses
• Non-alcoholic fatty liver disease (NAFLD)
• Polycystic ovary syndrome (PCOS) — often involves significant insulin resistance
• Cardiovascular disease — through multiple mechanisms
• Cognitive decline — Alzheimer’s has been called “type 3 diabetes” in some research framings

How to test for it

Several lab approaches, in order of insight:

Fasting glucose + fasting insulin (HOMA-IR calculation)

The most accessible early-detection screen. Requires fasting:

• Fasting glucose alone: detects late-stage problems (>100 mg/dL is prediabetic, >126 mg/dL diabetic)
• Fasting insulin: catches earlier-stage problems. Normal is <8-10 µIU/mL; >15 strongly suggests insulin resistance even with normal glucose
• HOMA-IR: calculated from both. Formula: (fasting glucose × fasting insulin) ÷ 405. HOMA-IR ≥2.5-3.0 suggests insulin resistance [^2]

Oral glucose tolerance test (OGTT)

Measures glucose (and sometimes insulin) at baseline and 2 hours after drinking 75 g of glucose. Catches abnormal glucose handling that normal fasting tests miss. Particularly useful for diagnosing PCOS-related insulin resistance and gestational diabetes.

HbA1c

Reflects average blood glucose over the prior 2-3 months. Useful but lags behind early insulin resistance (it doesn’t go up until glucose is consistently elevated).

• <5.7% — normal
• 5.7-6.4% — prediabetic
• ≥6.5% — diabetic

Most accurate diagnosis

The combination that catches early insulin resistance most reliably:

• Fasting glucose
• Fasting insulin
• HbA1c
• Sometimes: 2-hour post-meal glucose or formal OGTT

Many physicians won’t order fasting insulin without prompting — it’s worth asking specifically.

How to reverse it

Insulin resistance is genuinely reversible, especially early. The interventions, in approximate order of leverage:

1. Weight loss — particularly visceral fat reduction
2. Resistance training — improves insulin sensitivity meaningfully
3. Dietary changes — reduce refined carbohydrates and sugar; emphasize whole foods, adequate protein, fiber, fats
4. Sleep — sleep deprivation directly worsens insulin sensitivity
5. Address chronic stress — chronic cortisol elevation worsens insulin sensitivity
6. Medications when indicated — metformin is the first-line option for established insulin resistance with rising glucose; GLP-1 agonists are increasingly used (see GLP-1 glossary)

Insulin resistance vs. diabetes

The relationship:

• Insulin resistance can exist for years before glucose rises
• Prediabetes is the intermediate stage with rising glucose
• Type 2 diabetes is the late stage when β-cells can’t compensate

Acting in the insulin-resistance window (before diabetes) is dramatically more effective than acting after diabetes is established. This is the strongest argument for catching it early via fasting insulin testing.

Related entries

• Visceral fat
• GLP-1
• Cortisol