Normal Weight Obesity (NWO) is defined by a normal body mass index (BMI) coupled with an abnormally elevated percentage of body fat (PBF). This phenotype holds particular significance in patients with type 2 diabetes mellitus (T2DM), where altered body composition—namely diminished muscle mass and increased adiposity—may augment insulin resistance, cardiometabolic risk, and functional limitations. Bioelectrical impedance analysis (BIA) offers a practical and noninvasive approach to assessing body composition and uncovering occult obesity that is not detected by BMI-based classifications. This study sought to establish the prevalence of NWO among individuals with T2DM, characterize their clinical and body composition profiles, and examine the association between fat accumulation and metabolic indicators.

A cross-sectional investigation was conducted involving 122 adults diagnosed with T2DM per the 2024 ADA guidelines at University Medical Center Branch 2, Ho Chi Minh City. Anthropometric measurements, biochemical parameters, and body composition data (via BIA) were collected. Participants were categorized into three groups: non-obese, NWO (PBF ≥25% for men and ≥32% for women), and true obesity according to combined BMI–PBF criteria. Statistical analyses comprised t-tests, Mann–Whitney U tests, Chi-square tests, and correlation analyses using Pearson or Spearman coefficients, with statistical significance set at p < 0.05. Ethical approval was obtained from the institutional review board (No. 4079/ĐHYD-HĐĐĐ; October 09, 2025).

Approximately 28% of subjects exhibited the NWO phenotype. Individuals classified as NWO demonstrated normal BMI values (18.5–24.9 kg/m²) yet significantly increased PBF, alongside a pronounced inverse relationship between PBF and muscle mass (r = –0.76, p < 0.001). Additionally, the normal weight central obesity (NWCO) subgroup, defined by waist circumference thresholds (≥90 cm for men, ≥80 cm for women), reflected similar hidden adiposity patterns and a moderate negative correlation between PBF and muscle mass (r = –0.49, p < 0.001). These results highlight the discrepancy between BMI and actual adiposity status in T2DM.

Nearly one-third of T2DM patients present with the NWO phenotype, emphasizing the limitations of relying solely on BMI to evaluate adiposity within this population. The inclusion of BIA-derived metrics—specifically PBF and muscle composition—affords a more precise assessment of concealed obesity and sarcopenic–adiposity. Routine incorporation of body composition analysis into diabetes care may facilitate early identification of high-risk individuals and enable tailored, mechanism-driven interventions.