This article is from the Diet FAQ, by Claudia McCreary email@example.com with numerous contributions by others.
They're probably not the best answer for most people, since slurping down a
high-protein, low-fat, minimal calorie, blenderized concoction doesn't do
much to teach you the new, healthier eating habits that you'll need to
maintain your weight loss. These diets can also be expensive--an average of
US$2,000-3,000 for a medically-supervised six month plan--especially in
light of the fact that the "food" you're paying for isn't much more than
dried egg whites (an excellent source of protein) and flavoring. Although
nearly all liquid diet programs include classes to help participants ease
back into eating regular food and to maintain their weight loss, the ratio
of clients who actually maintain their new weight for long periods is low.
On the other hand, some obese people have found that the fast, steady weight
loss and ease of such diets (there's no need to plan menus) can help them
lose significant amounts of weight for the first time in their lives. Liquid
diets can succeed, but only if those who use them are dtermined to adopt
healthy eating habits once the diet is over.