This study serves as an initial comprehensive analysis of body composition in Japanese men with HIV over the age of 20 at a single center. Notably, our findings reveal a prominent rate of hidden obesity, accounting for a considerable proportion of the standard obesity rate (40.1%), underscoring the complex impact of ART on body composition. In Japan, obesity is defined as having a BMI ≥ 25 kg/m2, following a study [8] that highlighted the increased prevalence of hypertension, lipid disorders, hyperglycemia, and other conditions [9]. According to the National Health and Nutrition Survey conducted in Japan in 2019 [10], the prevalence of obesity among males was 23.1%, 29.4%, 39.7%, 39.2%, 35.4%, and 28.5% for those in their 20 s, 30 s, 40 s, 50 s, 60 s, and > 70 years, respectively.

This study found that 29.1% of participants and 53.0% in the normal BMI group had hidden obesity. Additionally, hypertension, diabetes, and lipid disorders were more prevalent among those with hidden or apparent obesity than in normal-weight individuals, indicating the importance of lifestyle guidance regardless of BMI.

The study further highlights the unique challenge of hidden obesity surpassing overt obesity in individuals with PLWH aged older than 60 years, signaling the risk of a surge in obesity rates within this group in the future. Although there is no clear mechanism for ART-induced weight gain, inflammatory markers, such as IL-6 and CRP, are more elevated in PLWH than in non-PLWH, even when the virus is well-controlled with ART [11]. These inflammatory markers cause insulin resistance and are associated with lifestyle diseases such as weight gain and diabetes [5]. In this study, CRP levels increased significantly from the NWG to the HOG to the OOG, suggesting an association between weight gain and chronic inflammation.

Classifying the body shapes (hidden obesity, normal, obesity) of Japanese individuals based on BMI and body fat percentage revealed that pulse wave velocity (an arterial stiffness indicator), HDL-C, LDL-C, and adiponectin significantly increased in the hidden obesity and obesity groups compared to the normal group, with no significant differences between the hidden and obesity groups [12]. These findings suggest that the prevention of lifestyle diseases is as important for patients with hidden obesity as it is for patients with obesity; however, it may be overlooked if body fat percentage is not measured.

The cross-sectional design limits linking body composition changes directly to ART. Future research should use longitudinal designs, include dietary analysis, and account for ART history to explore ART's comprehensive effects on body composition. These findings highlight the need for further studies with nutritional evaluations and interventions to improve PLWH's long-term health. This summary underscores the importance of advanced nutritional and lifestyle interventions in PLWH management, situating the study's implications in wider public health and clinical contexts.