Plenty of People Have ‘Normal’ BMI but Hidden Obesity, Study Finds

Your number on the bathroom scale could be misleading. New research finds that a substantial portion of people with “normal” weight still have obesity—and the higher risk of other health problems that goes along with it.

A large, international team of scientists examined survey data from the World Health Organization. They found that roughly one in five people worldwide with a healthy body mass index (BMI) show clear signs of abdominal obesity, or excess body fat. These skinny-fat individuals were also more likely to have conditions like high blood pressure. Doctors could be missing important health issues if they only focus on their patients’ BMI, the researchers say.

“Relying solely on BMI may be insufficient to identify these high-risk individuals and provide timely interventions,” they wrote in their paper, published this month in JAMA Network Open.

“Normal” but obese

BMI is calculated using a person’s weight and height, with obesity traditionally defined as having a BMI of 30 and over. In recent years, however, some doctors and patients have pushed for an expansion of what should be considered obese.

In January, a large group of obesity experts, backed by organizations like the American Heart Association, released alternative criteria for diagnosing obesity. This criterion asks doctors to either use BMI alongside one other measurement of excess body fat or to rely on these other measurements entirely. One such measurement is waist circumference.

In this new study, the researchers analyzed data from the WHO STEPS survey, a long-running project monitored by the WHO that allows countries to keep track of their residents’ risk factors for noncommunicable diseases, particularly those related to their lifestyle. In total, they looked at nearly a half million participants across 91 countries between 2000 and 2020.

All in all, 21% of respondents met the threshold for “normal-weight abdominal obesity,” meaning they had a healthy BMI but a large enough waistline to be categorized as obese. Compared to people with a normal BMI and healthy waistline, this group also had a higher prevalence of hypertension, high cholesterol, and diabetes, the researchers found.

Not just BMI

Other recent research has highlighted the importance of moving past BMI alone.

A study earlier this month, for instance, found that nearly 70% of Americans today meet the newer definition of obesity; this included 25% of Americans who had a normal BMI but other measures of excess body fat, such as waist circumference. This study also found that people with skinny obesity had a higher overall risk of health problems than nonobese people. That said, the authors of the latest study say theirs is the first to examine how common this form of hidden obesity is across the globe.

Rather than wholly abandon BMI altogether, the study researchers argue that doctors should use it in combination with these other measurements to truly get a better sense of their patients’ overall cardiovascular and metabolic health.

“Our findings suggest the need to use both BMI and waist circumference together, rather than in isolation, to provide a more complete and accurate assessment of cardiometabolic risk across diverse populations,” they wrote.

These results should also motivate the average person to get a thorough checkup at their next physical, one that doesn’t just stop at BMI.