Belly Fat, Not BMI, May Be the Deadliest Predictor of Heart-Kidney-Metabolic Disease

For decades, the body mass index has served as the first gatekeeper of metabolic risk assessment in clinics around the world. Step on a scale, have your height measured, and a single number determines whether a clinician flags you for further cardiovascular screening. But a large new population-based study is challenging the assumption that this number tells the whole story. Researchers analyzing nationally representative data from the United States have found that people of normal weight who carry excess fat around their midsection face the highest burden of cardiovascular-kidney-metabolic multimorbidity and, strikingly, the greatest risk of dying over long-term follow-up, even compared with people classified as obese. The findings, published in Clinical Research in Cardiology, suggest that where fat sits on the body may matter far more than how much of it there is overall.

The study drew on the National Health and Nutrition Examination Survey, or NHANES, covering survey cycles from 2007 to 2018, with mortality outcomes linked to the National Death Index through December 31, 2019. After applying survey weights, the analytic cohort represented approximately 106.9 million US adults, with a mean age of 47.2 years. Rather than relying on body mass index alone, the investigators stratified participants into four distinct body composition phenotypes using two measurements: BMI, which captures overall mass relative to height, and the waist-to-height ratio, which serves as a practical proxy for central or abdominal adiposity. The four groups were obesity with central adiposity, obesity without central adiposity, normal weight with central adiposity, and normal weight without central adiposity.

The distribution of these phenotypes across the American population proved revealing in its own right. A slim majority, 53.3 percent of the weighted cohort, fell into the normal weight without central adiposity category, the presumed metabolically healthy baseline. Another 33.9 percent carried both a high BMI and a high waist-to-height ratio, the classic pattern of generalized obesity. But two smaller and often overlooked groups drew the researchers’ attention: 8.1 percent of adults had normal BMI values but prominent central fat stores, a phenomenon sometimes called normal weight central adiposity, while 4.7 percent were obese by BMI yet lacked significant abdominal fat accumulation. These last two groups complicate the simple arithmetic of conventional obesity screening.

The central outcome of the investigation was cardiovascular-kidney-metabolic multimorbidity, defined as the coexistence of two or more of the following conditions: hypertension, hyperlipidemia, diabetes, chronic kidney disease, or established cardiovascular disease. This clustering of cardiometabolic disorders, increasingly framed under the umbrella of cardiovascular-kidney-metabolic syndrome, has been recognized by the American Heart Association as a major and growing driver of cardiovascular events and death. The syndrome reflects the intimate physiological coupling of the heart, kidneys, and metabolic organs: insulin resistance accelerates atherosclerosis, declining kidney function worsens volume overload and hypertension, and adipose tissue dysfunction amplifies inflammatory signaling that damages vascular beds throughout the body.

When the researchers tabulated multimorbidity prevalence across body composition phenotypes, a clear hierarchy emerged. Normal weight individuals with central adiposity had the highest rate of cardiovascular-kidney-metabolic multimorbidity at 46.5 percent, meaning nearly half of these apparently slim adults already carried at least two of the five defining conditions. This exceeded the multimorbidity burden observed in people with obesity with central adiposity, and it dwarfed the rates seen in the two phenotypes without abdominal fat excess. In other words, the single group that conventional BMI-based screening would most reliably classify as low risk was, by this metric, the sickest.

Mortality analyses sharpened the message considerably. Using survey-weighted Cox proportional hazards models, which allow researchers to estimate the association between a characteristic and the timing of death while adjusting for confounding factors and accounting for the complex sampling design of NHANES, the team found that normal weight adults with central adiposity faced an adjusted hazard ratio of 1.87 for all-cause mortality compared with the reference group, a statistically significant elevation with a 95 percent confidence interval of 1.08 to 3.25 and a p value of 0.025. Even more dramatic was the association with cardiovascular death: the adjusted hazard ratio reached 7.76, with a 95 percent confidence interval of 1.01 to 59.76 and a p value of 0.049. While the wide confidence interval reflects the relatively small number of events in this subgroup and should temper strong causal interpretation, the direction and magnitude of the association are consistent with a substantially elevated cardiovascular risk.

Kaplan-Meier survival curves, a standard technique for visualizing the probability of surviving over time across groups, reinforced the statistical models. Participants who combined cardiovascular-kidney-metabolic multimorbidity with the normal weight central adiposity phenotype demonstrated the poorest long-term survival of any group in the analysis, with the difference between curves reaching statistical significance at p less than 0.001. This convergence of evidence, spanning prevalence estimates, adjusted hazard modeling, and nonparametric survival analysis, points toward a coherent conclusion: the combination of a slim silhouette and a protruding waistline represents a particularly dangerous metabolic signature when it coexists with clustered cardiometabolic disease.

The biological plausibility behind these findings rests on the distinct behavior of visceral adipose tissue compared with subcutaneous fat. Fat deposited around internal organs is not an inert energy reservoir; it is a hormonally and immunologically active tissue that drains directly into the portal circulation, delivering free fatty acids and inflammatory cytokines to the liver and promoting insulin resistance, dyslipidemia, and hepatic steatosis. Visceral fat accumulation is also closely linked to ectopic fat deposition in the liver, pancreas, and heart itself, mechanisms that have been implicated in the progression of metabolic dysfunction-associated steatotic liver disease, type 2 diabetes, and atherosclerotic cardiovascular disease. A person with a normal BMI but a high waist-to-height ratio may therefore harbor a metabolically hostile internal environment that is invisible to weight-based screening, while some individuals with obesity and preserved fat distribution may be relatively protected.

The study arrives at a moment when the scientific community is actively rethinking how obesity itself should be defined. A recent international commission has proposed diagnostic criteria for clinical obesity that move beyond BMI toward measures of fat distribution and organ dysfunction, and prior research has repeatedly shown that waist-to-height ratio outperforms BMI as a screening tool for cardiometabolic risk factors. The new findings extend this literature into the specific arena of cardiovascular-kidney-metabolic multimorbidity and long-term survival in a nationally representative population. The authors conclude that normal weight individuals with central adiposity bear the greatest CKM burden and mortality risk, a result that highlights the limitations of BMI-based risk assessment and argues for incorporating simple anthropometric measures of central fat, such as the waist-to-height ratio, into routine clinical screening. For clinicians, the practical implication is straightforward: a tape measure around the waist may identify high-risk patients that the scale alone would miss, and for the public, the reassuring sight of a normal number on the bathroom scale should not be mistaken for a clean bill of cardiometabolic health.

Subject of Research: The association of body composition phenotypes with cardiovascular-kidney-metabolic multimorbidity and long-term mortality in a US population-based cohort

Article Title: Body composition phenotypes are key predictors of cardiovascular-kidney-metabolic multimorbidity and long-term mortality: insights from a population-based cohort study

Article References: Kong, G., Intaran, M. A. U., Soh, E. S. W., Yazicioglu, Y., Goh, R., Nagarajan, S., Wang, J.-W., Zhou, X., Zhou, X.-D., Zheng, M.-H., Chan, M. Y., Mehta, A., le Roux, C. W., Mamas, M. A., Khan, M. S., & Chew, N. W. S. (2026). Body composition phenotypes are key predictors of cardiovascular-kidney-metabolic multimorbidity and long-term mortality: insights from a population-based cohort study. Clinical Research in Cardiology. https://doi.org/10.1007/s00392-026-03010-5

Image Credits: AI Generated

DOI: 10.1007/s00392-026-03010-5

Keywords: cardiovascular-kidney-metabolic syndrome, central adiposity, body mass index, waist-to-height ratio, obesity, NHANES, multimorbidity, mortality, visceral fat, cardiometabolic risk, population-based cohort study, risk screening