Insulin resistance
Medically reviewed by Hormone Journal Editorial Team · Last reviewed 2026-05-17
Insulin resistance is a condition in which the body's cells don't respond normally to insulin, causing the pancreas to overproduce the hormone and raising blood sugar levels.
What it is
Insulin resistance is a condition in which the body's cells don't respond normally to insulin, causing the pancreas to overproduce the hormone and raising blood sugar levels. Insulin is a hormone made by the pancreas that acts like a key, unlocking cells so they can absorb glucose (blood sugar) for energy. When cells in the liver, skeletal muscle, and fat tissue stop responding well to that signal, blood sugar stays elevated and the pancreas compensates by releasing more and more insulin — a state called hyperinsulinemia (abnormally high insulin in the blood). Over time, the pancreas can't keep up, and blood sugar climbs into the prediabetes or type 2 diabetes range.
Causes and mechanism
No single cause explains insulin resistance; it typically results from several overlapping factors:
- Excess body fat, especially visceral fat (fat stored around the abdominal organs), releases inflammatory signals that interfere with insulin signaling at the cellular level.
- Physical inactivity reduces the number of glucose transporters in muscle cells, making them less efficient at absorbing sugar.
- Diet patterns high in refined carbohydrates and ultra-processed foods chronically elevate blood sugar and insulin demand.
- Hormonal conditions — including polycystic ovary syndrome (PCOS), Cushing's syndrome, and hypothyroidism — can worsen insulin sensitivity.
- Genetics play a role; a family history of type 2 diabetes meaningfully raises risk.
- Sleep deprivation and chronic stress raise cortisol, a hormone that opposes insulin's effects.
Researchers debate whether hyperinsulinemia itself drives resistance (a "chicken-and-egg" question), which has implications for treatment priorities.
Symptoms and diagnosis
Insulin resistance usually has no symptoms in its early stages. When symptoms do appear, they may include:
- Fatigue, especially after meals
- Difficulty losing weight despite calorie restriction
- Darkened skin patches in skin folds (acanthosis nigricans)
- Increased hunger or sugar cravings
Clinicians diagnose insulin resistance indirectly, because direct measurement (the hyperinsulinemic-euglycemic clamp) is a research tool, not a routine test. Standard clinical markers include:
| Test | Prediabetes threshold |
|---|---|
| Fasting plasma glucose | 100–125 mg/dL |
| HbA1c (3-month average blood sugar) | 5.7–6.4% |
| 2-hour oral glucose tolerance test | 140–199 mg/dL |
Fasting insulin levels and the HOMA-IR index (a calculated ratio of fasting glucose and insulin) are sometimes used but are not universally standardized.
Treatment options
Lifestyle change is the first-line treatment and the most effective:
- Weight loss of 5–7% of body weight has been shown in the CDC-recognized Diabetes Prevention Program to reduce progression to type 2 diabetes by 58% over 3 years.
- Aerobic and resistance exercise improve skeletal muscle glucose uptake independent of weight loss.
- Dietary changes — reducing refined carbohydrates, increasing fiber, and limiting ultra-processed foods — lower insulin demand.
When lifestyle changes are insufficient, clinicians may consider:
- Metformin, the most studied medication, reduces hepatic glucose production and is endorsed by the American Diabetes Association for high-risk prediabetes.
- GLP-1 receptor agonists (e.g., semaglutide) improve insulin sensitivity and promote weight loss; evidence for their use in prediabetes is growing.
- Treating underlying hormonal conditions (e.g., thyroid replacement, PCOS management) can substantially improve insulin sensitivity.
When to see a clinician
Request screening if you have any of the following: a body mass index (BMI) above 25, a waist circumference over 35 inches (women) or 40 inches (men), a first-degree relative with type 2 diabetes, a history of gestational diabetes, or PCOS. The American Diabetes Association recommends screening all adults starting at age 35, or earlier if risk factors are present. If a fasting glucose or HbA1c result falls in the prediabetes range, follow up within 3–6 months to discuss a structured prevention plan.
FAQs
What is the difference between insulin resistance and diabetes?
Insulin resistance is the underlying impairment in how cells respond to insulin; diabetes is the disease that results when blood sugar stays persistently above diagnostic thresholds (fasting glucose ≥126 mg/dL or HbA1c ≥6.5%). Insulin resistance typically precedes type 2 diabetes by 10–15 years, meaning there is a long window in which lifestyle changes can prevent progression. Not everyone with insulin resistance develops diabetes — the pancreas can compensate for years before failing to keep up.
Can insulin resistance be reversed?
Yes, in many cases. The landmark Diabetes Prevention Program trial showed that losing 5–7% of body weight through diet and 150 minutes of moderate exercise per week reduced the risk of progressing to type 2 diabetes by 58% over 3 years. Even without reaching a 'normal' weight, consistent physical activity and dietary changes can meaningfully improve insulin sensitivity. Reversal is harder once type 2 diabetes is established, though remission is possible with significant weight loss.
What are the best foods to eat if you have insulin resistance?
No single diet is universally endorsed, but evidence supports reducing refined carbohydrates (white bread, sugary drinks) and increasing fiber from vegetables, legumes, and whole grains, which slow glucose absorption and reduce insulin spikes. The Mediterranean and low-glycemic-index dietary patterns have the strongest research support for improving insulin sensitivity. A registered dietitian can help tailor an approach to your specific calorie needs and preferences.
Is insulin resistance the same as prediabetes?
They overlap but are not identical. Insulin resistance is the physiological mechanism; prediabetes is the clinical diagnosis given when blood sugar is elevated but below the diabetes threshold (fasting glucose 100–125 mg/dL or HbA1c 5.7–6.4%). You can have significant insulin resistance with blood sugar still in the normal range, because the pancreas is compensating. Prediabetes signals that compensation is beginning to fail. Approximately 96 million U.S. adults — more than 1 in 3 — have prediabetes, according to the CDC.
Does insulin resistance cause weight gain, or does weight gain cause insulin resistance?
Both are true, and they reinforce each other in a cycle. Excess visceral fat releases inflammatory signals that impair insulin signaling, promoting insulin resistance. At the same time, high circulating insulin levels encourage the liver to convert excess blood sugar into fat, contributing to further weight gain. Breaking the cycle usually requires addressing both sides simultaneously — reducing insulin demand through diet and increasing energy expenditure through exercise.