Short-Term, Significant Gains from a 10-Day Field-Based Multi-Modal Outdoor Activity Camp with Time-Restricted Feeding Dissipate at Three-Month Follow-Up

<b>Objectives:</b> This single-arm, pre-post intervention study with a three-month follow-up aimed to determine whether a ten-day outdoor camp combining mixed-modality physical activity and time-restricted feeding elicits positive changes in multiple body-composition outcome measures and whether those changes persist at three-month follow-up. <b>Methods:</b> Forty healthy undergraduates (18 male, 22 female) participated in a 10-day outdoor camp that combined multi-modal physical activities (rock climbing and bouldering, swimming, hiking, applied paddling, survival skills, etc.) with a 13 h daily time-restricted feeding window. Body fat percentage, skeletal muscle percentage, body mass, total body-water percentage, visceral fat level, and skeletal muscle index were measured using the InBody 270 at baseline, immediately post-camp, and at the three-month follow-up. <b>Results:</b> Mixed-effects models with random intercepts for subject revealed significant reductions in body fat percentage (<i>β</i> = -1.63, <i>p</i> < 0.001) and visceral fat level (<i>β</i> = -0.72, <i>p</i> = 0.001), alongside increases in skeletal muscle percentage (<i>β</i> = 1.02, <i>p</i> < 0.001), skeletal muscle index (<i>β</i> = 0.30, <i>p</i> < 0.001), and total body-water percentage (<i>β</i> = 1.19, <i>p</i> < 0.001) from baseline to post-camp; no outcomes differed between baseline and follow-up and no time × sex interactions were observed. <b>Conclusions:</b> These findings indicate that a brief, intensive nature-based intervention can drive rapid, multidimensional improvements in body composition, but structured maintenance is required to sustain benefits.