I think it is definitely possible but you would have to be very scrupulous about your choices.
It also depends what you deem 'healthy.'
I find eating clean to be synonymous with eating healthy. I try to eat 80% clean at all times typically.
This means abstaining from typical processed foods which is really found in most food establishments.
Just because you lose weight, maintain weight or don't notice negative symptoms rapidly doesn't mean that what you are doing is healthy.
So while it is possible, it is difficult and I find that most people who believe they are eating healthy (or nutritiously) for their body, are in fact, not.
We studied a lot of this in the multiple nutrition courses I took and what a lot of people produced as examples of healthy eating while they were out were not. One of the biggest issues is sauces, condiments and the like.
The issue at a lot of juice/smoothie places is the use of refined/processed sugar products. The average smoothie place where I live uses juice cocktails in their smoothies, the fruit is pretty processed so as to be more easy to deal promptly (typically puree's) and often the fibre is removed. They also use mass amounts of yoghurt or syrups in their smoothies as well.
I think one of the biggest issues to note, is serving size. People have really incorrect ideas about what is a proper portion and how to allocate those portions for different types of food. Your protein portion and your vegetable portion are not likely to be the same size if you follow traditional food portioning but I see a lot of people having their protein take up half their plate or more...