Aparently when you mash fruit (or make smoothies with them), it breaks down the cells/fibres in the fruit. Its the same with fruit juice.
Our slimming world consultant always explains is like this: If you tried to eat 30 oranges in one go you couldn't do it, If you made fruit juice from 30 oranges, you could drink it in one go probably, because all the fibre in the whole orange that fills you up has been broken down.
Also your body needs to work to break down a whole banana and doesnt need to if it is mashed. Totally agree with cheeky chops my slimming world consultant says exactly the same about not being able to eat loads of oranges but could drink lots.