Q. What's more important for health: my waist size or my weight?

A. The latest news: A measuring tape might be your best tool for tracking your overall health and longevity prospects. So toss out your scale, and forget those complex formulas for calculating your body mass index.

Many medical experts today agree that total body fat doesn't matter as much as fat distribution. Specifically, fat in your middle section can really do you in. Studies show that portly "apple" shapes (as opposed to the relatively healthier "pear" shapes who bulk up below the waistline) are at greater risk for type 2 diabetes, high cholesterol, high blood pressure, and heart disease.

How much belly fat raises a red flag? According to the Department of Health and Human Services, more than 40 inches (102 cm) around the waist for men and more than 35 inches (88 cm) for women qualifies as high risk. (And some experts suggest that these thresholds should be even lower.)

To measure yourself accurately, locate the top of your hipbone—which should be about navel height—and circle the tape all the way around bare skin, keeping the tape level and snug. Measure while breathing out normally—don't cheat by holding your breath or sucking in your stomach. If your belly is bigger than recommended, it's time to make some changes in your diet and exercise routine.

This Q&A was written by Victoria Dolby Toews, MPH, a health journalist based in the Pacific Northwest, where she and her family enjoy hiking and cycling.