According to one water fasting study, you can expect to lose around 6.6% of weight if you fast for 10 days assuming you’re a man…if you’re a woman and/or you’re planning on doing a longer/shorter fast, use this table to estimate your own results…but we’re talking total body weight, which includes water weight, glycogen-bound weight, sodium-bound weight, your muscle mass (because you’ll be losing the so-called structural protein throughout the fast), the feces that will leave your body during the fast, and last, but most definitely not least, your body fat. Also, you can expect to lose a lot less weight in total (but actually a bit more of your body fat) if you start a water fast after you’re already in ketosis.