Among 308,600 adults in the All of Us Research Program, each 0.05 rise in waist-to-height ratio (WHtR) carried hazard ratios of 1.07 to 1.31 across eight cardiometabolic outcomes. The signal was strongest in people with normal BMI: diabetes risk rose 52% per 0.05 WHtR in normal-BMI adults versus 22% in those with obesity. Of 77,684 normal-BMI adults, 31.3% had a WHtR of 0.50 or higher, and that group faced hazard ratios of 1.74 for diabetes, 1.49 for myocardial infarction and 1.52 for ischemic stroke.
This is the "normal-weight central obesity" phenomenon, quantified at scale: nearly one in three people whom BMI calls healthy carry waist-heavy fat distribution that predicts disease. The result fits earlier work, including meta-analyses favoring WHtR over BMI for cardiometabolic prediction, and UK guidance already endorses keeping waist below half your height. The practical takeaway is simple and free: measure your waist at the navel, divide by your height, and treat 0.50 or above as a prompt to discuss glucose and blood pressure screening with your doctor, even at a "healthy" BMI. Caveats matter. This is an observational cohort, so it shows association, not proof that shrinking waist lowers risk. All of Us skews toward people engaged with healthcare, and waist data and diagnoses may carry measurement and coding error. The modest discrimination gain suggests WHtR refines risk rather than transforming it. This is a preprint that has not been peer reviewed, so the figures may change. Editorially, it is confirmatory but useful, strengthening the case for routine waist measurement.