What is Insulin Resistance?

Insulin Resistance
Insulin Resistance is Improved by Exercise and Eating Right. webphotographeer E+/Getty Images

Insulin resistance is a decreased ability of some of the cells of the body to respond to insulin. It is the beginning of the body not dealing well with sugar (and remember that all carbohydrate breaks down into sugar in our bodies). One of insulin's main jobs is to get certain body cells to "open up" to take in glucose (or, more accurately to store the glucose as fat). Insulin resistance happens when the cells essentially don't open the door when insulin comes knocking.

When this happens, the body puts out more insulin to stabilize blood glucose (and so the cells can use the glucose). Over time, this results in a condition called "hyperinsulinemia" or "too much insulin in the blood." Hyperinsulinemia causes other problems, including making it more difficult for the body to use stored fat for energy.

What Causes Insulin Resistance?

We don't know the whole story, but certainly, genetics plays a big part. Some people are actually born insulin resistant. Lack of physical activity causes the cells to be less responsive to insulin. Most experts agree that obesity leads to more insulin resistance. However, it almost certainly also works the other way around: Insulin resistance promotes weight gain. So a vicious cycle can be set up with insulin resistance promoting weight gain, which promotes more insulin resistance.

What Problems Does Insulin Resistance Cause?

Besides general weight gain, insulin resistance is associated with abdominal obesity, high blood pressure, high triglycerides, and low HDL ("good cholesterol").

These conditions are part of a constellation of problems called metabolic syndrome (also called insulin resistance syndrome). Because this group of symptoms occurs together, it's hard to know what causes what, but metabolic syndrome is a risk factor for heart disease and Type 2 diabetes. 

How Common is Insulin Resistance?

Insulin resistance is becoming more common.

It also increases with age, which could be related to the tendency to gain weight in midlife. One study showed that 10 percent of young adults fit the criteria for the full metabolic syndrome, while the figure rose to 44 percent in the over-60 age group. Presumably, the prevalence of insulin resistance alone (without the full-blown syndrome) is much higher.

How Can I Tell if I Am Insulin Resistant?

If you are overweight, you are more likely to be insulin resistant, especially if you are carrying extra weight in your belly. If you have any of the symptoms of metabolic syndrome listed above, you are more likely to be insulin resistant. Additionally, people who respond well to reduced carbohydrate diets may be more likely to be insulin resistant. (See Different Diets for Different Bodies). I have based this article, "Is Low Carb For You?", partly on the premise that insulin resistant people are likely to benefit most from reducing carbohydrates in their diets.

Some experts use a fasting insulin test to help determine hyperinsulinemia and insulin resistance.

If Insulin Resistance is the First Step, What Comes Next?

If the pancreas keeps having to put out high levels of insulin, eventually it can't keep doing it.

The common explanation is that the beta-cells in the pancreas become "exhausted," but it actually may be that the high insulin and/or even slightly higher blood glucose starts to do damage to the beta cells. In any case, at that point, blood glucose starts to rise even more, and the path towards Type 2 diabetes is truly begun.

When fasting blood glucose reaches 100 mg/dl, it is called "prediabetes," and when it reaches 126, it is called "diabetes." You can see that these are invisible lines along a path of increasing inability for the body to deal with sugar: First, insulin is less effective, and then not enough insulin is available to do the job.

The sooner we can intervene in this process, the better off we will be.


Grundy, Scott, et al "Definition of Metabolic Syndrome." Circulation 109 (2004): 433-438.

Weir, Gordon and Bonner-Weir, Susan. "Five Stages of Evolving Beta-Cell Dysfunction During Progression to Diabetes." Diabetes 53 (2004): S16-S21.

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