Your bodies are just really good at self-preservation. They see the liquid diet as a famine and retain water. You might be dehydrated if you don't drink plenty of water. Metabolism varies so much by person.
Speaking of famine etc. I almost considered going on that lemon juice fast - you drink the juice of a lemon (supposed to be organic of course) mixed with a bottle of water (500 ml), 2 tablespoons of pure maple syrup and a dash of cayenne pepper.
The idea is to have six to eight of these per day for as long as you can stand it.
I actually did this back in 1995 when Josh went to visit his Dad in Alberta for a couple of weeks.
I think I lasted about 10 days. I did lose 20 pounds but I was a lot younger then!
It is supposed to give your digestive system a break. They also recommend salt water flushes, plus a mild laxative herbal tea
Was talking with a chiropractor a few years back and told him about this - he actually endorsed it and said that you can even clean out your gallbladder of stones using this regimen. It's pretty brutal but after awhile you don't even think about eating.
It makes you realize how much time we spend preparing food, eating it and cleaning up afterward so it is sort of a break. Hard to do if you have to prepare food for others, however.