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.