Six- and Twelve-Month Changes in Body Composition and 24-h Energy Expenditure After a Very Low-Calorie Ketogenic Diet

Objective: This study assessed changes in body composition and 24-h energy metabolism at 6 and 12 months after initiation of a 1-month very low-calorie ketogenic diet (VLCKD) in women with obesity. Methods: Seventeen women with obesity who completed a 1-month VLCKD underwent a 4-week transition phase with carbohydrate reintroduction, followed by a hypocaloric balanced diet. Assessments of body composition by dual-energy X-ray absorptiometry (DXA) and 24-h energy expenditure (24hEE) by a whole-room indirect calorimeter were performed. Results: Following the initial 7% weight loss, body weight further decreased at 6 months (-3.9%, p < 0.05), primarily driven by a significant decrease in fat mass (-10%, p < 0.05). From 6 to 12 months, three participants continued to lose weight, whereas most remained stable or partially regained. Lean soft tissue, decreased during the VLCKD phase, remained stable throughout follow-up. Both 24hEE and 24-h sleeping metabolic rate exhibited a progressive trend toward increase. Minute-by-minute 24hEE trajectories revealed a significant increase in metabolic rate from 1 to 6 months (p < 0.001). The metabolic adaptation observed after 1 month of VLCKD was no longer detectable at either 6 or 12 months. Conclusions: These findings provide novel insight into the physiological adaptations following VLCKD, supporting its role in supervised weight loss programs for selected patients. Trial registration: ClinicalTrials.gov identifier: NCT07418281.