Prolonged Water‐Only Fasting Followed by a Whole‐Plant‐Food Diet Promotes Fat‐Free Mass Recovery and Continued Fat Mass Loss in Adults With Overweight or Obesity

Introduction Conventional weight‐loss strategies often result in inadequate fat loss, poor sustainability, and unintended lean mass loss. Prolonged water‐only fasting followed by dietary change may offer an effective alternative, but its impact on body composition remains underexplored. Methods This secondary analysis utilized dual‐energy X‐ray absorptiometry (DXA) to assess changes in fat‐free mass (FFM), fat mass (FM), and bone mineral content (BMC) in adults [median (IQR) age: 62 (15) years with overweight or obesity. Participants underwent a median (IQR) of 14 (6) days of water‐only fasting, followed by 6 (3) days of food reintroduction with a whole‐plant‐food diet and a subsequent maintenance period of 45 (5) days. Study visits occurred at baseline and at the end of each period. Results At end of fasting, FFM accounted for 74% of total BW lost during fasting. However, at the follow‐up visit, the median (IQR) percentage change in total BW, FFM, FM, and visceral adipose tissue (VAT) mass from baseline was −8.2 (5.2), −4.4 (5.6), −14.7 (8.9), −15.8 (12.8) %, respectively. At follow‐up, FM loss accounted for 67% of the total BW lost. BMC remained unchanged across all study visits. Conclusions This protocol produced sustained FM loss, specifically VAT mass, and FFM recovery, suggesting it may support effective weight management.