The liquid diet for just one day seems to work well. He doesn't say to make it low-calorie, but he says not to make it fatty and heavy stuff - don't just liquify meatloaf, for example! And it's just one day a week.
I just have soup and juices. A smoothie, too, if I have the time and items for making one. I think it does end up being lower calorie.
One other of his recommendations that I like: sip hot water throughout the day. In a mug, really hot water. It's a good way for me to get my water 'quota.'
No clear head. My head is always muddled.