Insulin resistance means muscle, liver and fat tissue respond less to insulin, so the pancreas has to make more. Here is how it develops, how researchers measure it, the signs to know, and what studies show improves it.
Every time you eat, insulin helps move glucose out of the blood and into the cells that use or store it. Insulin resistance is a condition in which the body doesn’t respond to insulin the way it should 1. It is found in both lean and overweight people, and a Yale School of Medicine article puts it at about 40% of adults in the United States 8.
It can affect people with or without diabetes, and it can be temporary or long-lasting 2. It is also one reason glucose control can vary from day to day 6, 9, as our articles on exercise, sleep and the dawn phenomenon show.
In insulin resistance, cells in the muscles, fat and liver don’t respond well to insulin, so glucose has a harder time entering cells and blood glucose rises 1. Each tissue does a different job for insulin, and each can resist it in its own way.
After a meal, most of the glucose that leaves the blood is stored in muscle as glycogen, a chain of glucose molecules kept for later 10. Insulin makes this happen by moving glucose transporters to the muscle cell surface. In insulin-resistant muscle, less glucose gets in and less glycogen is made 10. In studies of lean adults, fat inside muscle cells predicted muscle insulin resistance much better than total body fat did, and muscle insulin resistance appears early in the course of type 2 diabetes 10.
After a meal, insulin tells the liver to store glucose as glycogen and to switch off the genes it uses to make new glucose. When the liver resists insulin, it stores less glycogen and glucose after meals runs higher 10. When muscle can’t take up glucose from a meal, more of it is diverted to the liver, which turns some of it into fat 10.
In fat tissue, insulin normally holds back lipolysis, the breakdown of stored fat. When fat tissue is inflamed and insulin-resistant, lipolysis speeds up, and the products push the liver to make more glucose 10. In most people, about 10% of body fat is visceral fat, packed around the liver, intestines and other organs. It makes more of the proteins called cytokines, which can trigger low-level inflammation 11.
In plain terms: Insulin tells muscle to take in glucose, tells the liver to stop releasing it, and tells fat cells to hold on to their fat. In insulin resistance, all three hear the signal less clearly, so the pancreas has to send more of it.
At first, the pancreas makes up for insulin resistance by releasing more insulin, a state called hyperinsulinemia, and glucose can stay in the usual range 2. Over time, the pancreas may not make enough insulin to keep up, and glucose rises 1. A 2016 review links the failure of the pancreas’s insulin-producing beta cells to high glucose and fat levels plus genetic factors 10.
This can unfold slowly. The Whitehall II study followed 6,538 British civil servants without diabetes for a median of 9.7 years; 505 developed type 2 diabetes 3. Insulin sensitivity fell steeply over the five years before diagnosis. Beta-cell function rose between four and three years before diagnosis, then fell. Fasting glucose crept up until about three years before diagnosis, then climbed from 5.79 to 7.40 mmol/L (104 to 133 mg/dL) 3.
Prediabetes is the stage in between. Diabetes Canada defines it as impaired fasting glucose (raised after an overnight fast), impaired glucose tolerance (raised 2 hours after a glucose drink) or an A1c of 6.0% to 6.4%, each of which places people at high risk of developing diabetes and its complications 5. Cut-offs from the US National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) start a little lower 1. People with prediabetes have a high chance of developing type 2 diabetes within 5 to 10 years 1.
| Test | Diabetes Canada | NIDDK (United States) |
|---|---|---|
| Fasting plasma glucose | 6.1 to 6.9 mmol/L (110 to 125 mg/dL) 5 | 5.6 to 6.9 mmol/L (100 to 125 mg/dL) 1 |
| 2-hour glucose tolerance test | 7.8 to 11.0 mmol/L (140 to 199 mg/dL) 5 | 7.8 to 11.0 mmol/L (140 to 199 mg/dL) 1 |
| A1c | 6.0% to 6.4% (42 to 46 mmol/mol) 5 | 5.7% to 6.4% (39 to 46 mmol/mol) 1 |
Insulin resistance does not always progress; mild insulin resistance may never turn into prediabetes or type 2 diabetes 2. Our mmol/L and mg/dL guide explains the units.
Metabolic syndrome is a cluster of risk factors for heart disease and type 2 diabetes. Criteria agreed in 2009 by the International Diabetes Federation, the American Heart Association and four other organizations 12, also used by Diabetes Canada 5, require at least three of these five 12:
Treatment for high triglycerides, low HDL, high blood pressure or high glucose also counts 12. The joint statement notes that most people with metabolic syndrome have abdominal obesity and insulin resistance 12, and Johns Hopkins Medicine agrees that most have insulin resistance 13.
Most people with insulin resistance or prediabetes have no symptoms 1. As the US Centers for Disease Control and Prevention puts it, you can’t tell if someone has insulin resistance by looking at them 14.
Acanthosis nigricans has other causes too, including high-dose niacin, birth control pills, corticosteroids and some cancers. Mayo Clinic advises seeing a health care provider about skin changes, especially sudden ones 4.
Insulin resistance is hard to measure directly, which is why routine blood work doesn’t report it.
In the glucose clamp, described in 1979, insulin is infused to hold blood insulin at about 100 µU/mL while glucose is infused at whatever rate keeps blood glucose at its usual fasting level 15. Once things are steady, the glucose infusion rate equals the glucose taken up by all the body’s tissues, so it measures their sensitivity to insulin 15. It is not a quick test: in one 2010 study, each clamp ran from 11:30 in the morning to 2:30 in the afternoon 9.
The homeostasis model assessment (HOMA), published in 1985, estimates insulin resistance and beta-cell function from fasting glucose and fasting insulin 16. In the original study, its insulin resistance estimate agreed closely with the clamp, a correlation of 0.88 where 1.0 is perfect agreement, but the authors noted low precision that limits its use 16. Large studies such as Whitehall II have used it 3.
NIDDK notes that health care professionals may not test for insulin resistance, and that the test is primarily used only for research studies 1. The 2023 international guideline on polycystic ovary syndrome (PCOS) adds that clinically available insulin assays are of limited clinical relevance and are not recommended in routine care 17. Instead, care teams look for the effects: Diabetes Canada diagnoses prediabetes and diabetes with fasting glucose, the 2-hour glucose tolerance test and A1c 5, and evaluation also draws on your history, a physical exam and a lipid panel 2.
| Measure | What it shows | Where it is used |
|---|---|---|
| Glucose clamp | How much glucose the body takes up while insulin is held high 15 | Research |
| HOMA-IR | An estimate of insulin resistance from fasting glucose and fasting insulin 16 | Research, including large studies 3 |
| Fasting glucose, 2-hour glucose test, A1c | Whether glucose is in the prediabetes or diabetes range 5 | Routine care |
| Waist, blood pressure, triglycerides, HDL | Metabolic syndrome criteria, which often travel with insulin resistance 12 | Routine care |
Some risk factors, such as age and family history, can’t be changed; weight, physical activity and smoking can 1.
Cleveland Clinic notes that no medicine treats insulin resistance specifically, and that lifestyle changes are the main approach 2. The research centres on three levers: activity, weight loss and sleep.
During a workout, aerobic exercise can raise muscle glucose uptake up to fivefold through routes that don’t need insulin 6. After prolonged exercise, uptake stays raised for about 2 hours through those routes and for up to 48 hours through insulin-dependent ones, as muscle refills its glycogen 6.
Regular aerobic training increases muscle insulin sensitivity in prediabetes and type 2 diabetes in proportion to how much exercise people do, resistance training enhances insulin action in a similar way, and both work even without weight loss 6. To enhance insulin action, the American Diabetes Association (ADA) recommends daily exercise, or at least no more than 2 days between sessions. In type 1 diabetes, aerobic training also decreases insulin resistance 6.
For people who use insulin or medicines that make the pancreas release insulin, exercise-induced lows are a known risk, most often within 6 to 15 hours after exercise, although the risk can extend to 48 hours 6. Our article on low blood sugar covers this.
In a randomized trial in adults with obesity, losing about 5% of body weight (5.1% on average, in 19 people) improved insulin sensitivity in fat tissue, liver and muscle, along with beta-cell function. Losing about 11% or 16% further improved beta-cell function and muscle insulin sensitivity 7. Yale researchers have found that modest weight loss lowers liver fat and reverses liver insulin resistance, and Gerald Shulman notes that a 10% weight reduction can make a big difference 8. In the Diabetes Prevention Program, people at high risk who lost 5% to 7% of their starting weight lowered their chance of type 2 diabetes, and the prevention or delay lasted at least 15 years 1.
In nine healthy adults, a night with 4 hours in bed (about 3 hours 46 minutes of sleep) was compared with a normal night 9. During a clamp the next day, glucose uptake fell from 40.7 to 32.5 µmol per kg of lean body mass per minute, about a fifth, and the liver released more glucose despite the insulin. The glucose needed to hold levels steady fell by about 25% 9.
Evidence that more sleep reverses this comes mainly from small studies. In 16 healthy young adults who habitually slept too little, adding an hour a night of time in bed for six weeks increased weekday sleep by about 44 minutes. Compared with their own baseline, those whose sleep rose most tended to gain the most fasting insulin sensitivity 18. Our article on sleep and glucose goes further.
Most people have no symptoms 1. The best-known sign is acanthosis nigricans, dark, velvety skin in the armpits, groin or neck 4. Skin tags can also be a clue 2.
Not in routine care. NIDDK notes that the test is primarily used only for research 1, where researchers use methods such as the glucose clamp and HOMA-IR 15, 16. Care teams check fasting glucose, A1c or a glucose tolerance test instead 5.
No. Prediabetes is defined by glucose or A1c above normal but below the diabetes range 5. Insulin resistance can be present while glucose is still normal, because the pancreas makes extra insulin to compensate 2.
It can improve. Losing about 5% of body weight improved insulin sensitivity in a randomized trial 7, and aerobic and resistance training improve insulin action even without weight loss 6. Some causes can’t be changed, but lifestyle changes can still help 2.
Yes. Insulin resistance can affect people with or without diabetes 2. The ADA’s position statement reports that aerobic training decreases insulin resistance in type 1 diabetes 6.
Insulin resistance doesn’t show up as a number in your logs, but the things that affect insulin sensitivity do. In Glyve’s day view, the glucose line shows your own target range, with logged meals, insulin, exercise, sleep and stress placed on the line, so you can compare an active day with a mostly seated one, or look at the day after a short night. You can log by typing, voice or photo, and each estimate is a draft you check before saving. The week view shows whether a pattern repeats. Glyve reads glucose from Apple Health, and Dexcom and FreeStyle Libre readings through those companies’ sharing services. Glyve shows what happened together; it doesn’t tell you what caused it. It isn’t a medical device and doesn’t give advice.
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