Insulin is an important hormone that controls many processes in the body.
However, problems with this hormone are at the heart of many modern health conditions.
Sometimes our cells stop responding to insulin like they are supposed to.
This condition is termed insulin resistance, and is incredibly common.
In fact, a 2002 study showed that 32.2% of the US population may be insulin resistant (1).
These numbers are scary, but the good news is that insulin resistance can be dramatically improved with simple lifestyle measures.
This article explains what insulin resistance is, why you should care and how you can overcome it.
Insulin and Insulin Resistance Explained
Insulin is a hormone secreted by an organ called the pancreas.
Its main role is to regulate the amount of nutrients circulating in the bloodstream.
Although insulin is mostly implicated in blood sugar management, it also affects fat and protein metabolism.
When we eat a meal that contains carbohydrates, the amount of blood sugar in the bloodstream increases.
This is sensed by the cells in the pancreas, which then release insulin into the blood.
Then insulin travels around the bloodstream, telling the body's cells that they should pick up sugar from the blood.
This leads to reduced amounts of sugar in the blood, and puts it where it is intended to go, into the cells for use or storage.
This is important, because high amounts of sugar in the blood can have toxic effects, causing severe harm and potentially leading to death if untreated.
However, due to various reasons (discussed below), sometimes the cells stop responding to the insulin like they are supposed to.
In other words, they become "resistant" to the insulin.
When this happens, the pancreas start producing even more insulin to bring the blood sugar levels down. This leads to high insulin levels in the blood, termed hyperinsulinemia.
This may continue to develop for a long time. The cells become increasingly more insulin resistant, and both insulin and blood sugar levels go up.
Eventually, the pancreas may not be able to keep up anymore and the cells in the pancreas may become damaged.
This leads to decreased insulin production, so now there are low amounts of insulin and cells that don't respond to the little insulin that is available. This can lead to skyrocketing blood sugar levels.
When blood sugar levels exceed a certain threshold, a diagnosis of type 2 diabetes is made. In fact, this is a simplified version of how type 2 diabetes develops.
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 are insulin resistant, then you have low insulin sensitivity. Conversely, if you are insulin sensitive then you have low insulin resistance.
Being insulin resistant is a bad thing, while being insulin sensitive is good.
Bottom Line: Insulin resistance implies that the cells are not responding well to the hormone insulin. This causes higher insulin levels, higher blood sugar levels and may lead to type 2 diabetes and other health problems.
What Causes Insulin Resistance?
There are many potential causes and contributors to insulin resistance.
One of the main ones is believed to be increased amount of fats in the blood.
This may be partly caused by fats and fatty acid metabolites building up inside muscle cells, termed intramyocellular fat. This disrupts the signalling pathways needed for insulin to work (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).
Having increased visceral fat, the dangerous belly fat that builds up around the organs, seems to be very important.
However, normal weight or thin people can also be insulin resistant, it is just much more common among those who are overweight (19).
There are several other potential causes of insulin resistance:
- Fructose: A high intake of fructose (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 the body may lead to insulin resistance (23, 24).
- Inactivity: Physical activity increases insulin sensitivity, and being inactive causes insulin resistance (25, 26).
- Gut microbiota: There is evidence that a disruption in the bacterial environment in the gut can cause inflammation that exacerbates insulin resistance and other metabolic problems (27).
This list is not definitive. There are many other factors that may affect insulin resistance/sensitivity.
Bottom Line: 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.
How to Know if You Are Insulin Resistant
There are several ways that your doctor can determine if you are insulin resistant.
For example, having high fasting insulin levels is a good sign of insulin resistance.
A test called HOMA-IR estimates insulin resistance from your blood sugar and insulin levels, and is fairly accurate.
There are also ways to measure blood sugar control more directly, such as an oral glucose tolerance test, where you are given a dose of glucose and then your blood sugar levels are measured for a few hours.
If you are overweight or obese, and especially if you have large amounts of fat around the belly area, then chances are very high that you are insulin resistant.
There is also a skin condition called acanthosis nigrans, involving dark spots on the skin that can indicate insulin resistance.
Having low HDL ("good" cholesterol) levels and high blood triglycerides are two other markers that are strongly associated with insulin resistance (3).
Bottom Line: Having high insulin levels and high blood sugar levels are key symptoms of insulin resistance. Other symptoms include lots of belly fat, high blood triglycerides and low HDL levels.
Insulin Resistance, Metabolic Syndrome and Type 2 Diabetes
Insulin resistance is a hallmark of two very common conditions, metabolic syndrome and type 2 diabetes.
The metabolic syndrome is a group of risk factors associated with type 2 diabetes, heart disease and other problems.
The symptoms are high blood triglycerides, low HDL levels, elevated blood pressure, central obesity (belly fat) and high blood sugar (31).
Sometimes this condition is referred to as the "insulin resistance syndrome" (32) Insulin resistance is also a major driver of type 2 diabetes. The high blood sugar levels are caused by the cells not responding to insulin anymore (33).
Over time, the insulin-producing cells in the pancreas may stop functioning, leading to insulin deficiency as well (34).
By stopping the development of insulin resistance, it may be possible to prevent most cases of metabolic syndrome and type 2 diabetes.
Bottom Line: Insulin resistance is at the heart of metabolic syndrome and type 2 diabetes, which are currently among the biggest health problems in the world.
Insulin Resistance is Linked to Heart Disease and All Sorts of Other Health Problems
Insulin resistance is also strongly associated with heart disease, which is the world's biggest killer (35).
In fact, people who are insulin resistant or have metabolic syndrome have up to a 93% greater risk of heart disease (36).
Bottom Line: Insulin resistance may cause a variety of diseases, including heart disease, non-alcoholic fatty liver disease, polycystic ovarian syndrome, Alzheimer's disease and cancer.
Ways to Reduce Insulin Resistance (Improve Insulin Sensitivity)
The good thing about insulin resistance, is that it is very easy to influence it.
In fact, you can often completely reverse insulin resistance by changing your lifestyle.
Here are several evidence-based ways to reduce insulin resistance:
- Exercise: This may be the single easiest way to improve insulin sensitivity. The effect is almost immediate (41, 42).
- Lose belly fat: Try to lose some fat, especially the deep "visceral" fat from your liver and belly. This article lists several evidence-based tips on how to lose belly fat.
- Stop Smoking: Tobacco smoking can cause insulin resistance, so quitting should help (43)
- Reduce Sugar Intake: Try to reduce your intake of added sugars, especially from sugar-sweetened beverages.
- Eat healthy: Eat a diet based mostly on whole, unprocessed foods. Include nuts and fatty fish.
- Omega-3 Fatty Acids: Eating omega-3 fatty acids can in many cases reduce insulin resistance. They can also lower blood triglycerides, which are often high in insulin resistant people (44, 45).
- Supplements: Taking a supplement called berberine can be effective to enhance insulin sensitivity and reduce blood sugar (46). Magnesium supplements may be helpful as well (47).
- Sleep: There is some evidence that poor sleep causes insulin resistance, so improving sleep quality should help (48).
- Reduce Stress: If excessive, try to manage your stress levels (49). Meditation has been shown to be helpful (50).
- Donate blood: High levels of iron in the blood are linked to insulin resistance. For men and postmenopausal women, donating blood may improve insulin sensitivity (51, 52, 53).
- Intermittent fasting: Following an eating pattern called intermittent fasting can improve insulin sensitivity (54).
Most of the items on the list also happen to be the same things we generally associate with good health, a long life and protection against disease.
All this being said, keep in mind that nothing in this article is intended as medical advice.
Insulin resistance is linked to various serious health problems, and I recommend that you speak to your doctor about your options. There are also various medical treatments that can work.
Bottom Line: Insulin resistance may be reduced or even completely reversed with simple lifestyle measures. These include exercise, eating healthy, losing belly fat and taking care of your sleep and stress levels.
Low-Carb Diets and Insulin Resistance
Another thing worth highlighting is low-carb diets.
Diets that restrict carbohydrates can have incredibly powerful benefits against metabolic syndrome and type 2 diabetes (55, 56), and this is partly mediated by reduced insulin resistance (57, 58, 59).
However, when carb intake is very low, such as on a ketogenic diet, the body may induce an insulin resistant state in order to spare blood sugar for the brain.
Bottom Line: Low-carb diets reduce the harmful insulin resistance linked to metabolic disease. However, very low-carb ketogenic diets may induce a harmless type of insulin resistance that spares blood sugar for the brain.
Take Home Message
Insulin resistance may be one of the key drivers of many (if not most) of today's chronic diseases, which are collectively killing millions of people every year.
Preventing insulin resistance may be among the single most powerful things you can do to live a longer, healthier and happier life.