Insulin is an important hormone that controls many bodily processes.

However, problems with this hormone are at the heart of many modern health conditions.

Insulin resistance, in which your cells stop responding to insulin, is incredibly common. In fact, over 32.2% of the U.S. population may have this condition (1).

Depending on the diagnostic criteria, this number may rise to 44% in women with obesity and over 80% in some patient groups. About 33% of children and teenagers with obesity may have insulin resistance as well (2, 3, 4).

Even so, simple lifestyle measures can dramatically improve this condition.

This article explains all you need to know about insulin and insulin resistance.

Insulin is a hormone secreted by your pancreas.

Its main role is to regulate the amount of nutrients circulating in your bloodstream.

Although insulin is mostly implicated in blood sugar management, it also affects fat and protein metabolism.

When you eat a meal that contains carbs, the amount of blood sugar in your bloodstream increases.

The cells in your pancreas sense this increase and release insulin into your blood. Insulin then travels around your bloodstream, telling your cells to pick up sugar from your blood. This process results in reduced blood sugar levels.

Especially high blood sugar can have toxic effects, causing severe harm and potentially leading to death if untreated.

However, cells sometimes stop responding to insulin correctly. This is called insulin resistance.

Under this condition, your pancreas produces even more insulin to lower your blood sugar levels. This leads to high insulin levels in your blood, termed hyperinsulinemia.

Over time, your cells may become increasingly resistant to insulin, resulting in a rise in both insulin and blood sugar levels.

Eventually, your pancreas may become damaged, leading to decreased insulin production.

After blood sugar levels exceed a certain threshold, you may be diagnosed with type 2 diabetes.

Insulin resistance is the main cause of this common disease that affects about 9% of people worldwide (5).

Resistance vs. sensitivity

Insulin resistance and insulin sensitivity are two sides of the same coin.

If you have insulin resistance, you have low insulin sensitivity. Conversely, if you are sensitive to insulin, you have low insulin resistance.

While insulin resistance is harmful to your health, insulin sensitivity is beneficial.

SUMMARY Insulin resistance occurs when your cells stop responding to the hormone insulin. This causes higher insulin and blood sugar levels, potentially leading to type 2 diabetes.

Many factors contribute to insulin resistance.

One is believed to be increased levels of fat in your blood.

Numerous studies show that high amounts of free fatty acids in your blood cause cells to stop responding properly to insulin (6, 7, 8, 9, 10, 11).

The main cause of elevated free fatty acids is eating too many calories and carrying excess body fat. In fact, overeating, weight gain, and obesity are all strongly associated with insulin resistance (12, 13, 14, 15).

Visceral fat, the dangerous belly fat that accumulates around your organs, may release many free fatty acids into your blood, as well as inflammatory hormones that drive insulin resistance (16, 18).

Although this condition is more common among those with excess weight, people with low or normal weight are also susceptible (19).

Other potential causes of insulin resistance include:

  • Fructose. High fructose intake (from added sugar, not fruit) has been linked to insulin resistance in both rats and humans (20, 21, 22).
  • Inflammation. Increased oxidative stress and inflammation in your body may lead to this condition (23, 24).
  • Inactivity. Physical activity increases insulin sensitivity, while inactivity causes insulin resistance (25, 26).
  • Gut microbiota. Evidence suggests that a disruption in the bacterial environment in your gut can cause inflammation that exacerbates insulin resistance and other metabolic problems (27).

What’s more, various genetic and social factors may be contributors. Black, Hispanic, and Asian peoples are at particularly high risk (28, 29, 30).

SUMMARY The main causes of insulin resistance may be overeating and increased body fat, especially in the belly area. Other factors include high sugar intake, inflammation, inactivity, and genetics.

Your health practitioner can use several methods to determine if you’re insulin resistant.

For example, high fasting insulin levels are strong indicators of this condition.

A fairly accurate test called HOMA-IR estimates insulin resistance from your blood sugar and insulin levels.

There are also ways to measure blood sugar control more directly, such as an oral glucose-tolerance test — but this takes several hours.

Your risk of insulin resistance increases greatly if you have excess weight or obesity, especially if you have large amounts of belly fat.

A skin condition called acanthosis nigricans, which involves dark spots on your skin, can likewise indicate insulin resistance.

Having low HDL (good) cholesterol levels and high blood triglycerides are two other markers strongly associated with this condition (3).

SUMMARY High insulin and blood sugar levels are key symptoms of insulin resistance. Other symptoms include excess belly fat, high blood triglycerides, and low HDL (good) cholesterol levels.

Insulin resistance is a hallmark of two very common conditions — metabolic syndrome and type 2 diabetes.

Metabolic syndrome is a group of risk factors associated with type 2 diabetes, heart disease, and other problems. It’s sometimes called insulin resistance syndrome, as it’s closely linked to this condition (31, 32).

Its symptoms include high blood triglycerides, blood pressure, belly fat, and blood sugar, as well as low HDL (good) cholesterol levels (33).

You may be able to prevent metabolic syndrome and type 2 diabetes by stopping the development of insulin resistance.

SUMMARY Insulin resistance is linked to metabolic syndrome and type 2 diabetes, which are among the world’s biggest health problems.

Insulin resistance is strongly associated with heart disease, which is the leading cause of death across the globe (34).

In fact, people with insulin resistance or metabolic syndrome have up to a 93% greater risk of heart disease (35).

Many other illnesses, including non-alcoholic fatty liver disease (NAFLD), polycystic ovarian syndrome (PCOS), Alzheimer’s disease, and cancer, are linked to insulin resistance as well (36, 37, 38, 39).

SUMMARY Insulin resistance is linked to various ailments, including heart disease, NAFLD, PCOS, Alzheimer's disease, and cancer.

It’s fairly easy to reduce insulin resistance.

Interestingly, you can often completely reverse this condition by changing your lifestyle in the following ways:

  • Exercise. Physical activity may be the single easiest way to improve insulin sensitivity. Its effects are almost immediate (40, 41).
  • Lose belly fat. It’s key to target the fat that accumulates around your main organs via exercise and other methods.
  • Stop smoking. Tobacco smoking can cause insulin resistance, so quitting should help (42).
  • Reduce sugar intake. Try to reduce your intake of added sugars, especially from sugar-sweetened beverages.
  • Eat well. Eat a diet based mostly on whole, unprocessed foods. Include nuts and fatty fish.
  • Omega-3 fatty acids. These fats may reduce insulin resistance, as well as lower blood triglycerides (43, 44).
  • Supplements. Berberine may enhance insulin sensitivity and reduce blood sugar. Magnesium supplements may be helpful, too (45, 46).
  • Sleep. Some evidence suggests that poor sleep causes insulin resistance, so improving sleep quality should help (47).
  • Reduce stress. Try to manage your stress levels if you easily get overwhelmed. Meditation may be particularly helpful (48, 49).
  • Donate blood. High levels of iron in your blood are linked to insulin resistance. For men and postmenopausal women, donating blood may improve insulin sensitivity (50, 51, 52).
  • Intermittent fasting. Following this eating pattern may improve insulin sensitivity (53).

Most of the habits on this list also happen to be associated with good health, a long life, and protection against disease.

That said, it’s best to consult your health practitioner about your options, as various medical treatments can be effective as well.

SUMMARY Insulin resistance may be reduced or even reversed with simple lifestyle measures, such as exercise, healthy eating, and stress management.

Notably, low-carb diets may fight metabolic syndrome and type 2 diabetes — and this is partly mediated by reduced insulin resistance (54, 55, 56, 57, 58).

However, when carb intake is very low, such as on a ketogenic diet, your body may induce an insulin-resistant state to spare blood sugar for your brain.

This is termed physiological insulin resistance and is not harmful (59).

SUMMARY Low-carb diets reduce the harmful insulin resistance linked to metabolic disease, though they may induce a harmless type of insulin resistance that spares blood sugar for your brain.

Insulin resistance may be one of the key drivers of many — if not most — of today’s chronic diseases.

Yet, you can improve this condition with simple lifestyle measures, such as losing fat, eating healthy food, and exercising.

Preventing insulin resistance may be among the most powerful ways to live a longer, healthier life.