Background <p>Obesity is a chronic, relapsing disease associated with substantial metabolic morbidity. While bariatric surgery and pharmacotherapy can be effective, their use may be limited by invasiveness, adverse effects, cost, or long-term accessibility. There remains a need for sustainable, non-invasive lifestyle-based strategies applicable in routine outpatient care. This study evaluated 10-year outcomes of a structured lifestyle-based nutritional intervention (metabolic endolipolysis) in adults with obesity.</p> Methods <p>This retrospective observational cohort study evaluated long-term outcomes of a structured outpatient nutritional intervention in a real-world clinical setting. A total of 100 adults with obesity (BMI ≥ 30&#xa0;kg/m²) were included. The intervention was based on a defined macronutrient composition with strict dietary fat limitation (approximately 30&#xa0;g/day), adequate protein intake (≥ 110&#xa0;g/day), and normoglycemic carbohydrate intake, combined with behavioral support and recommended daily moderate physical activity. Body composition was assessed annually using bioelectrical impedance analysis. Metabolic outcomes included HbA1c, fasting glucose, lipid profile, and liver enzymes.</p> Results <p>A mean fat mass reduction of 9.6&#xa0;kg was observed during the first year, with sustained reductions over the 10-year follow-up. Total fat mass decreased by 23.1%, including a 32.3% reduction in visceral fat, while lean body mass was largely preserved. Improvements were observed in metabolic parameters, including reductions in HbA1c (− 8.5%), LDL cholesterol (− 36.6%), and total cholesterol (− 30.0%). The greatest changes occurred within the first year and remained relatively stable thereafter. Adherence and retention appeared relatively high based on attendance at scheduled visits and self-monitoring; however, quantitative adherence metrics and validated assessment tools were not available.</p> Conclusions <p>This long-term observational study suggests that a structured lifestyle-based nutritional intervention delivered in an outpatient setting may represent a feasible, non-invasive component of obesity management. The intervention was associated with sustained improvements in body composition and selected metabolic parameters. These findings should be interpreted within the limitations of an observational design, including the absence of a control group, and warrant confirmation in randomized controlled trials.</p> Trial registration <p>Retrospective observational study; registration not required.</p>