A Large Waist May Point to Poor Insulin Function

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Karter AJ, D'Agostino RB, Mayer-Davis EJ, et al.: Abdominal obesity predicts declining insulin sensitivity in non-obese normoglycemics: the Insulin Resistance Atherosclerosis Study (IRAS). Diab Obes Metab 7:230–238, 2005.

What is the problem and what is known about it so far?

Some studies show a link between obesity and poor insulin sensitivity (when a person's insulin does not work like it should). Poor insulin sensitivity also increases a person's chance of getting cardiovascular disease (disease of the heart and blood vessels) and other health problems.

There are many ways to measure body weight and size, including body mass index (a measure of weight in relation to height) and waist size. Each method has plusses and minuses. However, obese people with extra body weight around their abdomens have greater health problems.

Why did the researchers do this particular study?

Researchers previously studied insulin sensitivity in people without diabetes. For this study, they wanted to study insulin sensitivity in the same group five years later, in order to find trends and differences.

Who was studied?

The study included 504 participants in the Insulin Resistance Atherosclerosis Study (IRAS) who were 40 to 60 years old and did not have diabetes. Participants were located in Oakland and Los Angeles, CA, San Antonio, TX, and San Luis Valley, CO.

How was the study done?

Participants had a physical exam, including measurement of their height and weight. They also had blood tests to assess insulin and glucose levels in their blood.

Participants were first studied during 1992 to 1994, then again in 1999.

What did the researchers find?

Participants with larger waist sizes were more likely to have poor insulin sensitivity than those whose excess weight was more evenly distributed throughout their bodies.

What were the limitations of the study?

There could be faults with how people were chosen for the study that could affect the findings. Neither body mass index nor waist size is a perfect method of measuring fatness. Other tests that determine whether fat is within the abdomen or just beneath the skin may have changed the findings. Also, tests of insulin sensitivity were done at the beginning of the study and five years later, but not during the study period.

What are the implications of the study?

Waist size may be a quick, easy, and inexpensive way to find out which people are most likely to have poor insulin sensitivity and heart and blood vessel disease.