Conversion Bariatric Surgery, Ketogenic Diet, and Intermittent Fasting in Bariatric Surgery Patients with Recurrent Weight Gain: a Prospective Randomized Controlled Trial

BACKGROUND: Recurrent weight gain (RWG) after metabolic and bariatric surgery (MBS) increases the need for alternative treatment strategies. This study evaluated the effects of conversion bariatric surgery (CBS), very low-calorie ketogenic diet (VLCKD), and time-restricted intermittent fasting (TRIF) on anthropometric measurements, biochemical parameters, and dietary habits in patients who experienced suboptimal clinical response (SCR) or RWG after bariatric surgery. METHODS: This study included 56 patients, allocated to four groups (CBS, VLCKD, TRIF, and control; n = 14 each). Weight, waist-hip measurements, body composition, glycemic/lipid profile, and serum levels of specific vitamins and minerals were assessed at baseline and at week 6. Energy and nutrient intakes were calculated using BeBiS-9. RESULTS: Data were analyzed with SPSS 22.0. The percentages of total and excess weight loss differed significantly among the groups (p < 0.001), with CBS (9.07–28.5%), VLCKD (9.12–31.85%), TRIF (5.09–14.97%), and control (0.97–3.40%). Additionally, the pre- and post-intervention differences in fasting insulin, HOMA-IR, HbA1c, cholesterol, LDL-C, triglyceride, and uric acid levels varied significantly among the groups. VLCKD showed a more prominent effect on glycemic parameters, whereas CBS had a more beneficial impact on the lipid profile. In intervention groups, daily energy, carbohydrate and fat intake (g/day) decreased; protein percentages increased; the frequency of consumption of energy-dense foods decreased; and healthy food preferences increased. CONCLUSIONS: Consequently, clinically significant improvements in weight management and metabolic parameters were observed in CBS, VLCKD, and TRIF groups under multidisciplinary team follow-up. These findings suggest that dietitian-led VLCKD and TRIF interventions may be considered as alternative treatment options before deciding on CBS.