In the body, food is broken down into glucose, the body’s main source of energy. Insulin is a hormone that helps cells convert glucose into energy.

Insulin resistance is a condition in which the body’s fat, muscle, and liver cells cannot use insulin properly. As a result, glucose builds up in the blood, while the cells do not get the glucose they need. In the long term, insulin resistance increases the risk of developing diabetes and heart disease. People who are insulin resistant do not experience any obvious symptoms.

Being overweight is a common risk for both cardiovascular disease and insulin resistance. To date, however, only a person’s waistline has been used to predict cardiovascular risk. Studies have shown that men with a waist circumference greater than 102 centimeters (40.2 inches) and women with a waist circumference greater than 88 centimeters (34.7 inches) are at an increased risk for heart disease. Could waist circumference also be used to gauge insulin resistance?

In a study published online on April 14, 2005 by the British Medical Journal , scientists report that waist circumference is a strong predictor of insulin resistance. They found that men and women with a waist circumference of less than 100 centimeters (39.4 inches) had a very low risk for insulin resistance; the risk of insulin resistance increased dramatically for those with a waist circumference greater than 39.4 inches.

About the Study

The researchers recruited 2,746 healthy volunteers, aged 18–72 years. The participants had waist circumferences that ranged from 65 centimeters (25.6 inches) to 150 centimeters (59.1 inches) and body mass indices (BMIs) that ranged from 18–60. (A healthy BMI is considered to be between 18 and 25.)

For each participant, the researchers measured waist circumference, systolic blood pressure, and body mass index.

They then took a blood sample from each volunteer to determine triglyceride levels, high-density lipoprotein (HDL) cholesterol, and insulin resistance.

The Findings

The researchers found that waist circumference predicted insulin resistance more strongly than triglyceride levels, HDL cholesterol, systolic blood pressure, or body mass index.

They determined that waist circumferences in both men and women without insulin resistance were very likely to be less than 39.4 inches. On the other hand, 94% to 98% of men and women with insulin resistance had a waist circumference greater than 39.4 inches. Relying on waist circumference alone to predict insulin resistance, however, is far from perfect. The researchers also found that in the population of men and women they evaluated, a waist circumference greater than 39.4 inches was able to accurately predict insulin resistance in only 61% of men and 42% of women. These numbers would presumably improve in populations where insulin resistance was more common.

How Does This Affect You?

This study highlights another link between abdominal fat and health. Previous studies have shown that a larger waist circumference increases the risk for cardiovascular disease. Now, this study demonstrates that people with a wide waistband are more likely to be insulin resistant, which is a major risk factor heart disease .

Fortunately, insulin resistance is reversible. By eating well and losing weight, you can help your body to use insulin more effectively. If you are unable to control or reverse insulin resistance, however, you will most likely be facing diabetes and perhaps even cardiovascular disease in the future.

If your waistline is over 39 inches and you are committed to its reduction, the place to begin is with your doctor. He or she can more precisely determine your risk for these conditions and recommend a course of action that you will need to take for the rest of your longer and healthier life.