Umm. Interesting question. I think much depends. How the dieter perceives the shakes, how much education goes along with the programme..and after.
But, I'm trying to think of a diet which only includes shakes for the whole 'journey' and can't think of any, though I'm sure there must be.
As for maintaining Whether you have more of a chance keeping it off if you've lost your excess weight on shakes alone (hypothetically as I don't know any), or whether you've lost on food, even that is possibly a little more complex that it appears.
Since maintenance has very little to do with the diet you lost the weight on (IMO), then my view is that it should make very little difference at all.
You would think that someone on 'real' food would do better than those just surviving on shakes, but there really are few diets out there where you learn to eating a balanced diet suitable for long term maintenance rather than a diet that is 'tweaked' to help weight loss along (ie, products that have been reduced in fat but with more additives, very low fat foods with very limited healthy fat additions, low carb etc.)
But as I say, few diets, if any rely totally on shakes alone for the whole duration, so I doubt much evidence is out there to support one way or another. I know that the main 'shake' diets in the UK include food as some stage; Cambridge can be done with food all along, and both LL and LT have 'real' food towards the end to get you back for portion control and healthy eating.
Slimfast has food too, though obviously a different type of 'shake' diet.
Very interesting question though
