You probably know your weight. You may even know your body mass index, or BMI. But researchers say there is another number worth knowing: your waist size.
A new Rutgers Health study found that measuring waist circumference may be one of the simplest ways to identify people carrying unhealthy amounts of body fat — and it performed nearly as well as more complicated methods using several body measurements.
That matters because excess fat around the abdomen is associated with increased risks for type 2 diabetes and heart disease. A person doesn’t necessarily have to look overweight or have a high BMI to carry too much abdominal fat.
“Pay attention to the need to loosen your belt or get bigger pants,” said Dr. Aayush Visaria, lead author of the Rutgers study. While clothing size isn’t a substitute for measuring your waist, he said changes can provide an early warning that you’re accumulating unhealthy amounts of body fat.
What Number Should You Know?
U.S. health guidelines have traditionally warned of increased health risks at a waist circumference greater than:
35 inches for women
40 inches for men
Those aren’t magic dividing lines between healthy and unhealthy. They’re screening thresholds indicating increased risk and should be considered along with blood pressure, cholesterol, blood sugar and other health factors.
The Rutgers researchers analyzed data from 1,900 U.S. adults ages 20 to 59 and compared several methods of identifying obesity with highly accurate measurements of body fat.
They found that using either BMI or waist circumference provided a good balance between identifying people with obesity and avoiding false diagnoses. Waist circumference alone performed nearly as well. BMI alone, however, missed a substantial number of people who had obesity based on their actual body-fat percentage.
Exactly Where Should You Measure?
This isn’t as obvious as it sounds.
Your “natural waist” — often considered the narrowest part of your torso or the area that creases when you bend sideways — isn’t necessarily where health professionals measure waist circumference. Your belly button isn’t necessarily the right spot either.
In fact, there are two commonly accepted medical methods.
U.S. National Institutes of Health guidance commonly uses the top of the hip bone, called the iliac crest, as the landmark. Place the tape horizontally around your abdomen just above the top of your hip bones.
The World Health Organization uses a slightly different method: find the bottom of your lowest rib and the top of your hip bone and measure halfway between the two.
Both methods are accepted ways of assessing abdominal fat. Research has found that the location used doesn’t substantially change waist circumference’s relationship with major health risks, although the actual number measured can differ somewhat. The important thing when tracking your waist over time is to choose one method and consistently measure at the same location.
Because the commonly used U.S. 35-inch and 40-inch risk thresholds are associated with the U.S. method, that’s a good method to use if you’re comparing your measurement with those numbers.
To measure correctly:
- Stand upright with your abdomen relaxed.
- Find the top of your hip bones on each side.
- Wrap a flexible tape measure horizontally around your body just above them.
- Make sure the tape is level all the way around and snug without digging into your skin.
- Breathe normally, then take the measurement after breathing out.
Don’t suck in your stomach.
Why It May Matter for Black Adults
Research suggests measurements of abdominal fat can provide useful information about health risks among Black adults as well.
A study of nearly 4,800 African-American adults participating in the Jackson Heart Study found that waist-to-height ratio was more strongly associated than BMI with several cardiovascular risk factors, including diabetes, high blood pressure, triglycerides and HDL cholesterol.
Waist-to-height ratio offers another simple guideline: keep your waist circumference below half your height. Someone who is 5-foot-6, or 66 inches tall, for example, would aim for a waist under 33 inches.
The takeaway isn’t to throw away the bathroom scale. Instead, researchers increasingly see waist circumference as another valuable measurement that may identify health risks BMI and weight alone can miss.
And unlike many medical tests, all it takes to check is a tape measure.