The research, led by Ava Aghakhani, Darya Rajabi, and Marziyeh Khoshkholgh of Tehran University of Medical Sciences, together with senior authors Solaleh Emamgholipour and Hossein Poustchi, drew on baseline data from the PolyIran-Liver cohort, a trial nested within the well-established Golestan Cohort Study in northern Iran. The analysis focused on 570 men aged 50 to 80 years, a demographic in which cardiometabolic disease burden is high and in which the limitations of BMI-based classification are particularly consequential. By cross-classifying participants according to body mass index and the presence or absence of metabolic syndrome, the investigators created six distinct obesity phenotypes: metabolically healthy obese, metabolically unhealthy obese, metabolically healthy overweight, metabolically unhealthy overweight, metabolically healthy normal-weight, and metabolically unhealthy normal-weight.

Against these six groups, the team measured an unusually broad panel of adiposity and organ-damage markers. Visceral fat thickness, a direct ultrasound estimate of the fat layer lining the abdominal cavity, was assessed alongside liver stiffness, a surrogate measure of hepatic fibrosis and fatty liver burden. Carotid intima-media thickness, an established marker of subclinical atherosclerosis, was also recorded. In parallel, the researchers calculated four lipid- and glucose-based indices from routine blood work: the visceral adiposity index, the lipid accumulation product, the body adiposity index, and the triglyceride-glucose index, commonly abbreviated as the TyG index. The central question was straightforward: which of these measures actually distinguish men who are obese but metabolically healthy from those who are lean but metabolically compromised?

The answer, published as an open-access article, is that no single index does everything, but the complementary strengths of the different measures map neatly onto the clinical problem. Visceral fat thickness, liver stiffness, and the body adiposity index all showed significant differences between obesity groups that shared the same metabolic status, meaning they tracked the sheer burden of excess fat rather than its metabolic consequences. In contrast, the triglyceride-glucose index and the visceral adiposity index separated metabolically healthy from metabolically unhealthy men within the same weight category, exactly the discrimination that BMI cannot provide. The lipid accumulation product stood out as the most versatile marker, differing significantly both across obesity categories at fixed metabolic status and across metabolic categories at fixed obesity status.

Regression analyses reinforced these patterns. When the researchers modeled the odds of elevated liver stiffness, the metabolically unhealthy obese, metabolically unhealthy overweight, and even metabolically healthy obese groups all showed significantly increased odds compared with the reference healthy phenotype, suggesting that excess fat mass itself, regardless of metabolic presentation, loads the liver with fibrogenic risk. The odds of an elevated lipid accumulation product were significantly raised in every non-reference group, underscoring the sensitivity of this simple measure, which is derived from waist circumference and fasting triglycerides, to deviations from metabolic health in either direction. Multiple linear regression models for visceral fat thickness, liver stiffness, and carotid intima-media thickness confirmed the group-level findings.

Perhaps the most sobering result was the one that failed to appear. Carotid intima-media thickness, the ultrasound marker of early arterial wall thickening, showed no significant differences across the six obesity phenotypes. In a cohort of older men, in whom decades of cumulative cardiovascular exposure may have homogenized atherosclerotic burden, the adiposity and metabolic indices did not translate into detectable differences in subclinical vascular disease. The authors are careful to note that this null finding should be interpreted within the specific context of their population and does not rule out associations in younger cohorts, in women, or in populations followed longitudinally rather than assessed at a single time point.

The technical logic behind the lipid-based indices helps explain why they outperform BMI. The visceral adiposity index integrates waist circumference, body mass index, triglycerides, and high-density lipoprotein cholesterol into a sex-specific estimate of visceral fat dysfunction, capturing not just how much fat is present but how pathologically it is behaving. The lipid accumulation product combines waist circumference with fasting triglyceride levels, effectively quantifying the lipid overflow that occurs when adipose tissue storage capacity is exceeded. The triglyceride-glucose index, a simple product of fasting glucose and triglycerides, serves as a proxy for insulin resistance, the central metabolic lesion linking obesity to type 2 diabetes and fatty liver disease. Because all three rely on measurements already collected in routine clinical practice, they could be deployed at scale without new equipment or expense.

The study’s imaging findings carry their own implications. Visceral fat thickness measured by ultrasonography emerged as a meaningful discriminator of obesity phenotypes, offering a radiation-free, bedside alternative to computed tomography and magnetic resonance imaging for quantifying the fat compartment most strongly linked to cardiometabolic risk. Liver stiffness measurement, likewise obtainable by ultrasound-based elastography, identified hepatic involvement even in men classified as metabolically healthy obese, a finding consistent with the growing recognition that so-called healthy obesity is frequently a transitional state in which organ damage precedes overt metabolic decompensation. For screening programs in resource-limited settings, the combination of ultrasound and routine blood chemistry may offer a pragmatic risk-stratification pathway that far outstrips the information content of a height and weight measurement.

The authors emphasize that their conclusions are bounded by the study design and population. The cross-sectional analysis captures a single moment in time and cannot establish whether the measured indices predict future cardiovascular events, diabetes, or liver disease progression. The cohort was exclusively male and exclusively older, spanning ages 50 to 80, so the findings cannot be directly generalized to women or to younger individuals in whom the physiology of adipose tissue distribution and metabolic risk may differ. The data derive from a secondary analysis of the PolyIran-Liver trial, originally funded by Tehran University of Medical Sciences, and the current analysis received no dedicated funding. The work was approved by the ethics committee of Tehran University of Medical Sciences and conducted in accordance with the Declaration of Helsinki, with informed consent obtained from all participants.

Even with those caveats, the study lands at a moment when the medical community is actively searching for alternatives to BMI. Recent debates over the definition of clinical obesity have called for measures that distinguish fat distribution and organ dysfunction from simple mass, and the new findings supply a concrete, low-cost toolkit for doing so in middle-aged and older men. The lipid accumulation product and the visceral adiposity index, the authors conclude, can be considered practical and inexpensive indices for metabolic risk stratification, while visceral fat thickness, liver stiffness, and the body adiposity index add anatomical and organ-level resolution that blood tests alone cannot provide. As health systems confront rising rates of obesity-related disease with constrained resources, the message of this research is that the next leap in obesity medicine may come not from new machines but from smarter use of the measurements clinicians already make every day.

Subject of Research: Comparison of visceral fat, liver stiffness, and lipid-based indices for classifying obesity phenotypes in older men

Article Title: Evaluating obesity phenotypes in men aged 50–80 years: comparative insights from visceral fat, liver stiffness, and lipid-based indices

Article References: Aghakhani, A., Rajabi, D., Khoshkholgh, M., Mohamadi, P., Mohammadi, Z., Emamgholipour, S., & Poustchi, H. (2026). Evaluating obesity phenotypes in men aged 50–80 years: comparative insights from visceral fat, liver stiffness, and lipid-based indices. BMC Endocrine Disorders. https://doi.org/10.1186/s12902-026-02548-9

Image Credits: AI Generated

DOI: 10.1186/s12902-026-02548-9

Keywords: obesity phenotypes, metabolic syndrome, visceral fat thickness, liver stiffness, visceral adiposity index, lipid accumulation product, TyG index, body adiposity index, carotid intima-media thickness, BMI limitations, cardiometabolic risk, Golestan Cohort Study