Building Up Resistance

In people who have neither diabetes nor insulin resistance, eating a typical meal will cause blood glucose levels to rise, triggering the pancreas to produce insulin. The hormone travels through the body and induces fat and muscle cells to absorb excess glucose from the blood for use as energy. As the cells take up glucose, blood glucose levels fall and flatten out to a normal range. Insulin also signals the liver—the body's glucose repository—to hold on to its glucose stores for later use.

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However, people with insulin resistance, also known as impaired insulin sensitivity, have built up a tolerance to insulin, making the hormone less effective. As a result, more insulin is needed to persuade fat and muscle cells to take up glucose and the liver to continue to store it.

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In response to the body's insulin resistance, the pancreas deploys greater amounts of the hormone to keep cells energized and blood glucose levels under control. (This is why people with type 2 diabetes tend to have elevated levels of circulating insulin.) The ability of the pancreas to increase insulin production means that insulin resistance alone won't have any symptoms at first. Over time, though, insulin resistance tends to get worse, and the pancreatic beta cells that make insulin can wear out. Eventually, the pancreas no longer produces enough insulin to overcome the cells' resistance. The result is higher blood glucose levels (prediabetes) and, ultimately, type 2 diabetes.

Insulin has other roles in the body besides regulating glucose metabolism, and the health effects of insulin resistance are thought to go beyond diabetes. For example, some research has shown that insulin resistance, independent of diabetes, is associated with heart disease.