The revised definition of obesity, introduced by The Lancet Diabetes and Endocrinology Commission, expands how body fat is measured.
Traditionally, obesity has been determined by body mass index, a calculation based on height and weight. The new guidelines add other measurements, such as waist circumference, waist-to-height ratio, and waist-to-hip ratio. These measures help identify people who may have excess abdominal fat even if their weight falls within a normal range.
Researchers examined more than 300,000 Americans through National Institutes of Health’s All of Us Research Program. Under the new definition, obesity rates rose from 42.9 percent to about 68.6 percent. The impact is especially pronounced in older age groups, with nearly 80 percent of adults over 70 now meeting the new criteria.
Dr. Lindsay Fourman, an endocrinologist and one of the study’s authors, called the findings “astounding.” She said the results highlight the need to rethink how obesity is treated and prevented.
The new classification splits obesity into two categories. “BMI-plus-anthropometric obesity” applies to people who have both a high BMI and at least one elevated body fat measure. “Anthropometric-only obesity” applies to those with a normal BMI but at least two elevated fat measurements.
The study found that people with anthropometric-only obesity were at higher risk for diabetes, cardiovascular disease, and mortality than those without obesity. Senior author Dr. Steven Grinspoon said this group was previously overlooked because they did not meet the old BMI-based definition.
About half of the individuals who met the new guidelines showed signs of clinical obesity, meaning obesity was already affecting their health or organ function.
At least 76 medical organizations, including American Heart Association and The Obesity Society, have endorsed the new framework. Researchers say more work is needed to understand how to treat those newly classified as obese, especially older Americans who face higher risks from excess abdomial fat.
Dr. Fourman said body composition, not just weight on a scale, should guide future health strategies. “Identifying excess body fat is very important as we’re finding that even people with a normal BMI but with abdominal fat accumulation are at increased health risk,” she explained.