Modified Fasting Followed by an Alternating Low-Carbohydrate Mediterranean Diet (carbo-switch diet): Long-Term Weight and Cardiometabolic Outcomes after ≥10 Years of Follow-Up. A Retrospective Real-World Analysis over 16 Years of Clinical Practice: Carbo-Switch Diet: 10-Year Outcomes

Background: Long-term maintenance of weight loss after intensive dietary interventions remains a major challenge in obesity care. The “Alternant metabolic model” (Carbo-switch) combines an initial phase of protein-sparing modified fasting followed by alternating low-carbohydrate days and a structured Mediterranean maintenance strategy (5+2 pattern). Objectives: To evaluate long-term (≥10 years) outcomes on weight maintenance, waist circumference, incident type 2 diabetes, and mortality following a sequential dietary program. Methods: Retrospective, monocentric observational study including 260 adults with obesity or overweight (mean age 49.3 ± 9.8 years; 63.1% women; BMI 33.4 ± 4.8 kg/m²). The intervention included 15 days of protein-sparing modified fasting (400–600 kcal/day), ≥6 months of alternating very-low-carbohydrate and hypocaloric Mediterranean days, followed by long-term Mediterranean maintenance using a 5+2 weekly pattern. After a mean follow-up of 11.2 ± 2.1 years, survival status was assessed and survivors were contacted to collect data on weight, adherence, waist circumference, and glycemic outcomes. Results: At follow-up, 18 patients (6.9%) were deceased (61% cardiovascular). Among 242 survivors, 146 (60.3%) maintained adherence, while 48 discontinued within the first year and 48 were not reachable. Mean weight loss at 6 months was −17.6 ± 5.2%. At ≥10 years, adherent participants maintained a net weight loss of −10.6 ± 5.3% versus −2.4 ± 4.9% in non-compliant individuals. Waist circumference decreased from 108 ± 11 cm to 96 ± 10 cm in adherent participants versus 103 ± 11 cm in non-compliant. Among individuals without baseline diabetes (n = 160), incident diabetes was 15.8% in adherent patients compared with 32.5% in non-compliant. Conclusions: A sequential dietary strategy combining modified fasting, carbohydrate alternation, and long-term Mediterranean 5+2 maintenance is associated with sustained clinically meaningful weight loss, durable waist reduction, and lower incidence of type 2 diabetes in real-world practice. Long-term adherence appears to be the main determinant of success.