Insulin Resistance

What insulin resistance is

After you eat, blood sugar rises and the pancreas releases insulin. Insulin signals muscle and fat cells to absorb glucose and tells the liver to stop making more. In insulin resistance this signal is weakened:

• Muscles take up less glucose after meals.
• The liver keeps releasing glucose, especially overnight, and turns excess into fat.
• Fat tissue keeps releasing fatty acids into the blood, which worsens resistance in the liver and muscles.

To overcome the resistance, the pancreas pumps out more insulin. High insulin (hyperinsulinemia) keeps glucose normal for a while, often years. When the pancreas can no longer keep up, blood sugar rises into the prediabetes range and then into type 2 diabetes.

Signs and symptoms of insulin resistance

Insulin resistance itself has no specific symptoms. Signs that it is likely present include:

• A large waist: fat stored around the organs (visceral fat) is the strongest predictor
• Acanthosis nigricans: dark, thick, velvety skin in body folds, a direct effect of high insulin on skin cells
• Skin tags, especially many on the neck and armpits
• High triglycerides and low HDL ("good") cholesterol
• High blood pressure
• Fatty liver on an ultrasound or raised liver enzymes
• Irregular periods, acne and excess hair growth from PCOS
• Rising fasting glucose or A1C on blood tests

Tiredness after meals, sugar cravings and difficulty losing weight are often attributed to insulin resistance, but they are nonspecific and common in people without it.

What causes insulin resistance

Main drivers

• Excess visceral fat: fat cells inside the abdomen and liver release inflammatory signals and fatty acids that interfere with insulin.
• Physical inactivity: muscles are the largest user of glucose. Exercise makes them more insulin-sensitive within hours.
• Genetics and ethnicity: risk is higher with a family history of type 2 diabetes and in people of South Asian, Hispanic, Black, Native American and Pacific Islander descent, often at a lower body weight.
• Age: insulin sensitivity declines with age and muscle loss.

Other contributors

• Short or poor sleep, and untreated sleep apnea
• Smoking
• Diets high in refined carbohydrates, sugary drinks and ultra-processed foods
• Medicines: glucocorticoids (steroids), some antipsychotics, some HIV medicines, thiazide diuretics and statins (small effect)
• Hormonal conditions: polycystic ovary syndrome, Cushing syndrome, acromegaly
• Pregnancy, which causes temporary insulin resistance by design; when the pancreas cannot keep up, gestational diabetes results

Insulin resistance, prediabetes and metabolic syndrome

How insulin resistance is tested

There is no single routine test, because the gold-standard measurement (the clamp test) is a research tool. In practice, doctors use:

• A1C and fasting glucose to check whether blood sugar has risen
• Oral glucose tolerance test, which can pick up early problems after a sugar drink
• Lipid panel: a triglyceride-to-HDL ratio above about 3 (in mg/dL) suggests insulin resistance in many populations
• Waist circumference and blood pressure
• Fasting insulin and HOMA-IR (a calculation from fasting insulin and glucose): useful in research and some clinics, but there is no agreed cutoff, and insulin assays vary between labs, so major guidelines do not recommend them for routine diagnosis
• Liver tests or ultrasound for fatty liver

How to reverse insulin resistance

Insulin resistance responds well to lifestyle change, often within weeks.

Lose a modest amount of weight

Losing 5% to 7% of body weight, about 10 to 14 lb (4.5 to 6.5 kg) for someone weighing 200 lb (91 kg), improves insulin sensitivity substantially. In the landmark Diabetes Prevention Program, this level of weight loss plus 150 minutes of weekly activity cut progression to type 2 diabetes by 58%. Loss of liver and belly fat matters most.

Move more, and build muscle

• Aim for at least 150 minutes a week of moderate activity, such as brisk walking.
• Add strength training 2 or more days a week: more muscle means more glucose uptake.
• A 10 to 15 minute walk after meals blunts blood sugar spikes.
• Break up long periods of sitting.

Eat for steadier blood sugar

• Cut sugary drinks and fruit juice first; they have a large effect.
• Choose high-fiber carbohydrates: vegetables, beans, lentils, whole grains, whole fruit.
• Include protein and healthy fats at meals.
• Limit refined starches, sweets and ultra-processed foods.

Mediterranean-style, lower-carbohydrate and calorie-reduced diets all improve insulin resistance. The best plan is one you can keep up.

Sleep and stress

Aim for 7 to 9 hours of sleep. Even a few nights of short sleep measurably worsen insulin sensitivity. Treating sleep apnea also helps.

Medicines

• Metformin lowers liver glucose output and is used for prediabetes in higher-risk people, and in PCOS.
• GLP-1 receptor agonists (such as semaglutide) and tirzepatide cause substantial weight loss and improve insulin sensitivity. They are prescribed for obesity or diabetes, not for insulin resistance alone.
• Pioglitazone directly improves insulin sensitivity and is used in some people with diabetes and fatty liver.

Supplements such as berberine, cinnamon and inositol are widely promoted. Evidence is limited or mixed, and they should not replace proven treatment.

Complications if it is not addressed

• Type 2 diabetes
• Heart attack and stroke, through high blood pressure, abnormal cholesterol and inflammation
• Fatty liver disease, which can progress to MASH (steatohepatitis) and cirrhosis
• PCOS-related infertility
• Gestational diabetes in pregnancy
• Possibly higher risk of some cancers

Frequently asked questions

What are the signs of insulin resistance?

Most people have no symptoms. Clues include a large waist, dark velvety skin patches on the neck or armpits, many skin tags, high triglycerides, low HDL cholesterol, high blood pressure, fatty liver and a rising A1C. In women, irregular periods, acne and extra hair growth can point to PCOS-related insulin resistance.

Can insulin resistance be reversed?

Yes, in most people it can be greatly improved. Losing 5% to 10% of body weight, exercising regularly including strength training, sleeping 7 to 9 hours and cutting sugary drinks and refined carbohydrates restore much of the body's insulin sensitivity, sometimes within weeks.

How do I get tested for insulin resistance?

Ask your doctor for an A1C, fasting glucose and cholesterol panel, and have your waist and blood pressure measured. These identify insulin resistance and its consequences. Fasting insulin or HOMA-IR can add information, but they are not standardized and are not routinely recommended.

Can you have insulin resistance if you are thin?

Yes. Genetics, inactivity, low muscle mass, poor sleep, some medicines and fat stored inside the abdomen or liver can cause insulin resistance at a normal weight. This is more common in people of South Asian and East Asian descent.

What is the best diet for insulin resistance?

There is no single best diet. Plans that cut sugary drinks and refined starches, emphasize vegetables, legumes, whole grains, lean protein and healthy fats, and create a modest calorie deficit all work. Mediterranean-style and lower-carbohydrate approaches have good evidence. Consistency matters more than the exact plan.