People often watch the number on the bathroom scale when they are worried about weight. But a new study suggests another number may deserve just as much attention: the measurement around the waist.
Researchers at Rutgers Health found that waist circumference alone can do a good job of identifying people who carry unhealthy amounts of body fat. The research was published in JAMA Network Open and may help make obesity screening easier in clinics and at home.
Obesity is more complicated than simply weighing too much. Body fat can be stored in different places, and fat that builds up around the middle of the body is often more closely tied to health problems than fat stored elsewhere.
This is one reason doctors have become increasingly interested in waist size. A larger waist can be a sign of fat collecting deep inside the abdomen around organs such as the liver and intestines, and this type of fat is linked with problems in the way the body handles blood sugar and fats.
For many years, BMI has been the most familiar way to screen for obesity. It is calculated from height and weight, making it easy to use, but it cannot show how much of a person’s weight comes from fat, muscle or bone.
BMI also does not tell doctors where fat is located. A muscular person can have a high BMI without having too much body fat, while another person can have a BMI outside the obesity range but still carry a large amount of fat around the abdomen.
A group of independent experts recently proposed a broader way of identifying obesity. Their approach uses several measurements, including BMI, waist circumference, the relationship between waist and height, and the relationship between waist and hip size.
Rutgers researchers wanted to find out whether this more detailed method offered enough extra value to justify the additional measurements. They studied about 1,900 adults ages 20 to 59 using information from the U.S. National Health and Nutrition Examination Survey.
The researchers had access to an accurate measure of participants’ body fat, allowing them to compare different screening methods with a stronger reference point. This helped them see which methods found people with excess fat and which methods incorrectly labeled people as having obesity.
The more detailed framework did identify a larger number of people with high body fat. Yet the researchers found that a much simpler rule based on either BMI or waist circumference offered a better balance between finding true cases and limiting false alarms.
Even more striking, waist circumference on its own came close to the performance of the more complicated approaches. That finding could be useful because measuring a waist takes little time, costs almost nothing and can be added to an ordinary medical visit.
The study also showed why BMI should not always be used by itself. Some participants had body-fat levels that met the study’s obesity criteria even though BMI alone did not identify them, meaning their possible health risk could have been missed.
Lead author Aayush Visaria said people may even notice early changes through everyday life, such as a belt becoming tighter or pants no longer fitting comfortably. Clothing size is not a substitute for a proper measurement, but a growing waist can be a signal worth paying attention to.
Waist size should still be viewed as one piece of a larger health picture. Someone with a larger waist does not automatically have diabetes or heart disease, and doctors also need to consider blood pressure, blood tests, smoking, activity, diet, medical history and other factors.
There are also questions that this study cannot answer. The participants were younger than 60, and the research focused on how well measurements identified excess body fat rather than whether a particular waist measurement would predict who later developed disease or died early.
Even with those limits, the study has an important practical message. Health screening works best when people can actually use it, and a simple waist measurement may provide much of the information gained from a set of more complicated body measurements.
The findings also support a wider shift away from treating BMI as the only important number. Future studies should test these simple methods in older people and different populations and examine how well they predict future disease, but waist circumference appears to be a useful, low-cost warning sign that deserves more attention.
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Source: Rutgers University.
