What Is Insulin Resistance and Why Does It Matter?
Written by: Claudia S. Copeland, PhD
Reviewed by: Emily J., MSc RD
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Insulin resistance is a metabolic condition that affects 4 out of every 10 non-diabetic American adults. But what is insulin resistance, and how does it develop? Can you reverse it?
Insulin resistance is a metabolic condition brought about by factors such as a diet high in processed, high-carbohydrate foods; a sedentary lifestyle; excess body fat; genetics; and even some hormonal syndromes . If left unchecked, it can progress to pre-diabetes, in which blood sugar levels are higher than normal, and then on to Type 2 diabetes, metabolic syndrome, nonalcoholic fatty liver disease, and other cardiovascular problems [2,3,4]. A staggering 4 in every 10 non-diabetic American adults under the age of 44 experience insulin resistance, but how can you tell if you’re developing it ? Even more importantly, can you reverse it?
Before we talk about insulin resistance, we need to say a bit about glucose, a simple sugar found naturally in a variety of foods, including starchy vegetables and grains such as corn, rice, potatoes, and wheat, as well as honey and fruits.
Your body breaks down all the carbohydrates you consume into glucose, its preferred energy source. We’ve evolved to depend on glucose because it’s the most abundant monosaccharide (simple sugar) in nature, and the easiest to be converted into energy by mitochondria, the engines of our cells . In other words, glucose was essential to our survival in the pre-agricultural conditions in which our ancestors lived, where sugary and fatty foods (read: high-calorie and energy-rich) were scarce and hunter-gatherers sometimes roamed up to 500 miles to search for food [7,8].
Before supermarkets existed, our ancestors might have gone most of the day with little food before encountering a trove of honey, a cluster of bananas, or another sugary food. To keep a steady supply of energy, the body needed to store additional calories for later — and evolved to deal with this situation by utilizing a hormone called insulin .
If we think of energy as money for the body, insulin can be considered the “money manager” hormone. In life, when you get a sudden cash influx, you decide, based on how much cash you have on hand and how much you need for your current expenses, whether to spend it, put it in a checking account, or put it into a long-term savings account. In the body, insulin performs a very similar role, directing glucose to where it should go based on the body's current needs.
Let's say you just ate a ripe banana and a PB&J on white bread. Your blood glucose levels will rise due to your sudden large intake of carbohydrates. In response to this biochemical “cash infusion,” the pancreas (an organ near your stomach, liver, and gallbladder) releases insulin, which carries the glucose into cells via specialized transporters [10,11]. The first order of business is for insulin to transport glucose into cells that need to burn it right away, like active muscle cells. But if there's more glucose than the cells need for current "expenses" (i.e., necessary energy to put to use in the cells immediately), the insulin sends the glucose to be built into a short-term storage molecule called glycogen.
Glycogen is like a checking account. It stores energy but is easily broken down to withdraw that energy when needed. A small amount of glycogen is stored in the muscles and other cells for their own use, but most is stored in the liver, where it can be broken down into glucose that's released into the blood for use by any cells in the body, including brain cells.
If the body's stores of glycogen fill up and there's still excess glucose around, insulin transports it into fat cells (which you can think of as a savings account or rainy-day fund) for long-term storage .
When we consistently consume a diet high in glucose (an easy feat in the modern world, where we have 24/7 access to processed snacks and beverages), our insulin-based storage system becomes stressed. Essentially, the storage units for excess calories become full, and just as an overstuffed bag starts bursting at the seams, the body's energy storage system starts to break down.
In an attempt to avoid damage, your fat cells take action to prevent more glucose from being packed into them when they are already overstuffed . (This can happen, incidentally, in people who do not appear to be overweight. It is not a matter of visible body type; it is a matter of the existing fat cells in a body being overly enlarged past their healthy storage levels.)
These actions result in cells becoming less and less responsive to insulin in terms of their glucose uptake, requiring the pancreas to release more and more insulin to do the same job. When insulin loses its ability to do its job in this way, you develop insulin resistance .
It’s important to note that not all cases of insulin resistance are linked to excessive sugar consumption, and diet alone is not the only driving factor behind a faulty insulin response. Researchers have found that chronic stress and inflammation, lack of proper gut bacteria, and bad sleep are all associated with a greater risk of developing insulin resistance.
The best way to tell if you’ve developed insulin resistance is by getting your blood glucose tested at your doctor’s office. The three most common tests for this are the fasting plasma glucose test, oral glucose tolerance test, and hemoglobin A1c test. However, some people with insulin resistance have telltale signs, such as a darkening of the skin around the armpits or the neck, known as acanthosis nigricans; small cutaneous (skin-related) growths called skin tags or other cutaneous abnormalities; or an enlarged waistline ("apple shape") [14,15]. If the situation has become more severe and you’ve progressed into hyperglycemia (high blood sugar), you may feel tired and thirsty while also needing to urinate frequently, or hungry even though you've already eaten .
Since most people with insulin resistance don’t experience any noticeable symptoms, it’s key to see your doctor for routine bloodwork and lead a balanced lifestyle (such as eating a wide range of vegetables, fruits, and healthy fats; exercising regularly; and managing your stress).
If insulin resistance isn’t brought under control, it can lead to serious diseases such as Type 2 diabetes, atherosclerosis, and non-alcoholic fatty liver disease [17,18,19]. It can also lead to weight gain, which is associated with a number of poor health outcomes . The immediate effects of insulin resistance can take a toll on your day-to-day performance, too: poor sleep, fatigue, and trouble concentrating can make it difficult to function [21,22]. Meanwhile, insulin resistance can trigger a vicious cycle where you develop cravings for high-carb foods that impair metabolic health and make insulin resistance even worse .
If you are showing signs of insulin resistance, there are straightforward steps you can take to reverse it.
Weight can have a significant impact on insulin sensitivity. A study on adult women between the ages of 24 and 40 found that those who had maintained lost weight demonstrated enhanced insulin sensitivity compared to BMI-matched controls with no weight loss history . On the other hand, women who had previously lost weight but regained it afterward demonstrated impaired insulin sensitivity. Researchers studying overweight and obese women found that maintaining a 15% reduction in body weight for 12 months had improved insulin sensitivity .
When you exercise, your body breaks down glycogen (your checking account with energy to spend) and frees up glucose to burn, which in turn clears “storage” space. This can be used to store even more glucose during your next carbohydrate-rich meal, rather than forcing insulin to direct it to your fat cells.
Research also correlates certain types of exercise with improved insulin sensitivity and/or lower risks of developing metabolic syndrome. One 2017 study, for example, found that even less than one hour of resistance training per week (without additional aerobic exercise) reduced the risk of developing metabolic syndrome . Another group of studies found that 2-3 resistance training sessions for at least 8 weeks improved insulin sensitivity by up to 48% .
A single night of bad sleep can result in a measurable increase in insulin resistance in healthy people . But getting good sleep involves a few factors, including sleep timing and variability. In other words, not just the time you go to bed and wake up, but the consistency of your sleep routine. A 2020 systemic review found that later sleep timing and greater sleep variability are associated with increased cardiometabolic risk and other adverse health outcomes .
Eating fiber is a great way to lower your blood glucose levels and reduce your risk of developing insulin resistance . One study compared insulin sensitivity in people who ate a high-fiber diet with people who ate a high-protein diet . Both of these groups lost weight in similar amounts (both diets restricted fat to 30% of calories), but they showed a striking difference when it came to insulin: after 6 weeks on the diet, the high-fiber group was 25% more sensitive to insulin than the high-protein group. Similar results have been found in other studies looking at fiber and insulin sensitivity.
Psychosocial stress is correlated with insulin resistance, likely through the stress hormone cortisol, which can hinder insulin secretion . In addition to reducing stress through exercise (even just two days per week of aerobic exercise can help reduce anxiety), studies show that mindfulness practices like meditation can help to reduce your physiological stress response [33,34].
Monitoring your blood sugar levels in real time can provide you with a wide array of insights that help inform specific and long-term lifestyle changes, many of which can improve your insulin sensitivity. You can learn to identify the foods that trigger glucose spikes as well as understand how your specific responses to exercise timing, sleep patterns, and periods of stress or inactivity are contributing to your glucose levels (and, by proxy, your insulin response).
Insulin resistance is one of the leading contributors to our current metabolic health crisis, though addressing it isn’t as simple as eating a healthy diet. In addition to genetic and hormonal conditions, factors such as sleep, exercise, stress, and weight can all enhance or impair your insulin sensitivity — and incorporating the following strategies into your life can help you avoid insulin resistance altogether or reverse it: