Perirenal fat: a neglected fat depot shaping heterogeneity of obesity along with hepatic fat.

Objective: Obesity is a heterogeneous condition that leads to diverse cardiovascular and metabolic outcomes. This study aimed to identify the primary visceral fats contributing to metabolically unhealthy obesity and to investigate the characteristics of fat distribution associated with different obesity-related complications.

Methods: A retrospective analysis was conducted on fat-selective magnetic resonance images (MRI) from 319 individuals with a BMI ≥24 kg/m². Participants were categorized into four groups: solely obesity, T2DM, hypertension, and dyslipidemia, to examine differences in the distribution of hepatic, pancreatic, preperitoneal, mesenteric, and perirenal fat (PrFT). Correlation analyses were performed to elucidate relationships between visceral fat deposits and obesity-related characteristics. Logistic regression identified key fat deposition sites associated with common obesity-related complications. Additionally, the limitations of single-site fat measurements in capturing the heterogeneity of obesity were examined.

Results: PrFT exhibited the strongest correlation with blood pressure (r = 0.225 ~ 0.306, all p < 0.001) among all visceral fats, and the hypertensive individuals with obesity presented the highest PrFT. Hepatic fat showed the highest association with glucose metabolism (r = 0.188 ~ 0.407 all p < 0.01), as evidenced by higher hepatic fat content in the T2DM group compared to other groups. Risk of metabolic syndrome increased by 3.06-fold (95% CI:1.35-6.93, p = 0.007) and 6.79-fold (95% CI:2.45-18.83, p < 0.001) with moderate and severe fatty steatosis compared to those without hepatic steatosis. A 2.24-fold (95% CI:1.27-3.97, p = 0.006) increase in metabolic syndrome likelihood was observed for each 1 cm increment in PrFT.

Conclusions: Besides hepatic fat, perirenal fat is also a key determinant for metabolic syndrome. Patients with various metabolic abnormalities present distinct patterns of visceral fat distribution, which could be simply profiled by perirenal and hepatic fat quantification.