Background: To compare sex-specific body composition changes after a structured lifestyle intervention in Hungarian Defence Forces (HDF) personnel and to describe baseline dietary, behavioral, and psychological profiles. Material and Methods: This quasi-experimental pilot study included 40 active-duty participants (21 men, 19 women), aged 24–55 years, enrolled in an ongoing HDF lifestyle program. The 6-month intervention integrated individualized dietary counselling, supervised physical training 3 times weekly, and weekly cognitive-behavioral group sessions. Body composition was assessed at baseline (D0) and after 6 months (D1). Psychological, behavioral, and physical activity variables were assessed at baseline only as profile measures. Results: At baseline, age and body mass index (BMI) did not differ significantly between sexes. Men had higher body weight, skeletal muscle mass, visceral fat, and phase angle, whereas women had higher body fat percentage. In both sexes, body weight, BMI, and body fat percentage decreased significantly over 6 months. In men, body weight decreased by mean±standard deviation (M±SD) 9.25±11.68 kg (p = 0.001), BMI by M±SD 2.73±2.97 kg/m² (p = 0.007), body fat percentage by M±SD 3.77±4.94 percentage points (pp) (p = 0.011), and skeletal muscle mass increased by M±SD 1.70±3.58 kg (p = 0.029). In women, body weight decreased by M±SD 5.79±5.88 kg (p = 0.005), BMI by M±SD 2.27±2.47 kg/m² (p = 0.024), and body fat percentage by M±SD 2.66±3.53 pp (p = 0.030), whereas skeletal muscle mass increased non-significantly by M±SD 1.13±1.76 kg (p = 0.063). Baseline profiles were otherwise similar, except for higher energy intake in men and higher eating behavior scores in women. Conclusions: In this pilot sample, participation in a structured multidisciplinary lifestyle intervention was associated with meaningful body composition improvements in both sexes, although response patterns differed. These findings support further evaluation of tailored multidisciplinary lifestyle interventions in military occupational health practice. Med Pr Work Health Saf. 2026;77(3)