Normal weight on the scale. High risk in the abdomen. For 5.89 million American adults, those two facts coexist, and the standard clinical screening tool used to catch them is missing the signal entirely.

Among adults with a normal BMI (18.5 to 24.9) but a waist circumference above high-risk thresholds (greater than 88 cm for women, 102 cm for men), 39.5% have dysglycemia, meaning prediabetes or diabetes. That's more than double the 18.5% rate among normal-BMI adults whose waist circumference falls within normal range. Two people can walk into a clinic with identical BMIs and face metabolic risk profiles that are worlds apart.

When the Scale Says Fine but the Abdomen Disagrees

The gap isn't subtle. Diabetes prevalence alone runs at 11% among normal-BMI adults with high-risk waist measurements, compared to 5% among their normal-waist counterparts. Prediabetes-only prevalence is 28.5% versus 13.5%. These aren't marginal differences. They're the kind of gaps that, in a screened population, would trigger entirely different clinical pathways.

The practical consequence is direct: a patient cleared by BMI-only screening may leave a clinical encounter without a glucose test, without a referral, and without any awareness that their abdominal fat distribution places them in a high-risk metabolic category. At a population level, that's a systematic gap in early detection for a condition where early intervention demonstrably changes outcomes.

The 5.89 million adults in this category represent a small fraction of the 55.08 million normal-BMI adults with normal waist circumference, but their dysglycemia burden is disproportionate. A group that's roughly one-tenth the size carries more than twice the metabolic risk rate.

Older Adults and the Waist-BMI Divergence

The mismatch between BMI classification and waist-based risk doesn't distribute evenly across age and race. Among Non-Hispanic Asian adults aged 70 and older with normal BMI, 21.4% exceed high-risk waist thresholds (note: this subgroup has a sample of 35). That's a striking figure given that standard BMI cutoffs were not designed with Asian body composition in mind, and clinical guidelines for Asian populations often recommend lower BMI thresholds precisely because of this kind of divergence.

Non-Hispanic Black adults show a similar age gradient. High-risk waist prevalence among normal-BMI individuals in that group rises from 11% in the 60-69 age range to 13.1% among those 70 and older. By contrast, Non-Hispanic White adults aged 18-29 with normal BMI show a 2.7% high-risk waist prevalence, based on a sample of 170.

The pattern across groups points to a consistent dynamic: as age increases, the gap between what BMI captures and what waist circumference reveals tends to widen. For older patients who are already at elevated metabolic risk, that gap has direct clinical consequences.

What 39.5% Actually Means at Scale

Put the numbers together and the picture is clear. Among the 5.89 million normal-weight Americans with high-risk waist measurements, nearly four in ten already have dysglycemia. More than one in ten have diabetes. These aren't people on a trajectory toward metabolic disease. A substantial share are already there.

The open question isn't whether waist circumference adds predictive value over BMI. The data on that is unambiguous. The question is what proportion of those 5.89 million individuals have ever had their waist measured in a clinical setting, received a glucose test, or been told they carry elevated metabolic risk at all. Given that BMI remains the dominant screening metric in routine care, the answer is almost certainly: not enough.