Weight Loss and Long-Term Weight Trajectories After a Structured Nutritional and Behavioral Intervention: A Large Real-World Cohort Study

Background/Objectives: Achieving and maintaining intentional weight loss is a major challenge in routine clinical practice, and real-world evidence is limited. Methods: This retrospective cohort study evaluated initial weight loss in 56,093 adults from a total of 126,659 who commenced the French RNPC program between 2013 and 2025, and subsequent weight trajectories in 2395 participants with 4-year follow-up data. The intervention combined an energy-restricted, protein-enriched, low-glycemic-load diet with individualized dietary and behavioral support, followed by progressive food reintroduction and optional long-term follow-up. Results: During the weight-loss phase (median, 4.6 months), median body weight decreased by 11.0 kg (12.7%) and waist circumference by 12.0 cm (11.8%), while lean mass percentage increased by 1.3 percentage points. At 4 years, among the 2395 participants with available follow-up data, median weight remained 7.8 kg (9.1%) and waist circumference 10.0 cm (9.8%) below baseline. Longitudinal mixed-effects models using all available repeated measurements showed similar patterns in weight, BMI, waist circumference, fat mass, waist-to-height ratio, and relative fat mass at 4 years. Conclusions: These findings show substantial initial weight loss and long-term maintenance of clinically meaningful reductions in weight and waist circumference among participants with 4-year follow-up data after a structured nutritional and behavioral intervention in routine clinical practice.