Losing 8 pounds in 5 days would require a daily deficit of 5,600 calories, so if you ate nothing you would still need to burn 3,600 calories to hit that, and if you’re hiking with a moderate load at a relaxed pace you’d be burning around 500-600 calories and hour, so would need to be hiking for like 7 hours a day AND not eating anything to lose that much weight in that much time…