For a person to live on a liquid diet for life, what would they have to drink every day?

Ensure? Boost? Any type of meal replacement shake? Juice?

Your body doesn't absorb solids, it takes the nutrients out of food as a liquid and processes the liquids into your cells for energy. For example when you eat an apple, it's like you ran a steam roller over the apple, digested the juice and the little flat piece left on the pavement would be passed through your system as waste.

But you need to eat foods that contain fiber (like what's left of the apple) to keep your body's food processing system working properly. There is a lot of evidence that many of the problems people have with their intestinal systems like colon cancer are due to lack of fiber in their diet.

If the diet contained all of the nutrients you need, including fiber, the fact that it was consumed in liquid form wouldn't hurt.