Your waistline is a window to your heart's health. Waist size is a better predictor of heart disease than total body fat, new research shows.

It probably won't shock you to learn that larger waists mean greater heart disease risk. It's no secret that being out of shape is a major risk factor for heart disease.

Now, scientists have pinpointed the exact numbers to watch out for.

Using a tape measure is easier than calculating your body mass index (BMI), and it's also better at assessing heart disease risk, say the researchers in February's American Journal of Clinical Nutrition.

Body mass index (search) is based on your height and weight. It's an indirect measure of total body fat.

A BMI of 25 to 29.9 is overweight, and a BMI of 30 or higher is obese. Those are the danger zones that can indicate greater heart disease risk.

Data came from more than 10,000 people participating in a national survey.

The researchers, including the Medical College of Wisconsin's (search) Shankuan Zhu, MD, PhD, didn't just check participants' weight and height. They also looked at waist measurements, blood sugar, high blood pressure, and cholesterol levels.

Waist Size Better Than BMI

The researchers found that waist size correlated better than BMI with risk factors for heart disease — high blood pressure, blood sugar and cholesterol.

For example, waist size was a better predictor of a person's blood pressure than BMI.

In 2002, a study in the same journal also favored the easily measured waist size over BMI for predicting risk of heart disease.

Men should strive for a waist size of 35 inches or under and women 33 inches or under. This correlates to a normal BMI of under 25 — and a lower risk of heart disease.

Apple or Pear Shape?

Lots of Americans are overweight. According to the CDC, 15 states had adult obesity rates of 15 percent to 19 percent in 2003. Another 31 states had rates of 20 percent to 24 percent, and in four states more than a quarter of the population was obese.

Where the extra pounds lie may make a difference. Larger waists, or an "apple" shape, indicate abdominal fat. Fat around the hips and thighs is often described as a "pear" shape.

Studies have linked abdominal fat to more health problems, including increased risk of diabetes and breast cancer.

Either way, following a safe, sensible nutrition and exercise program can get you back on track. Experts, including doctors, fitness trainers, and therapists, can help. With a healthy, long-term approach, your waist will shrink — and your heart will thank you.

By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: Zhu, S. American Journal of Clinical Nutrition, Feb. 2005; vol 81: pp 409-415. WebMD Health Tools: "BMI Calculator." CDC, "U.S. Obesity Trends 1985-2003." WebMD Medical News: "Body Fat Distribution Linked to Diabetes." WebMD Medical News: "Watching Your Waist May Reduce Breast Cancer Risk." WebMD Medical News: "Does Waist Size Affect Your Heart?"