Of COURSE you CAN drink as much juice as you like! However, if weight loss is an issue, you will want to drink closer to the three cup limit. Paavo Airola recommends 3-6 cups daily, and in my experience this is LOTS of juice! The stuff is packed with nutrients.
I have done extra long (up to 48 days) on The Master Cleanser , which consists of only lemon juice, natural maple syrup and water with a pinch of cayenne... and worked out every day. You NEED much less than you think, unless you have special needs (hypoglycemic, diabetic etc.).