A diet of just protein smoothies?

I think the problem is that as soon as you start eating again, you'll do it exactly like before. Dieting on shakes won't do anything to teach you portion control, or about what your body needs. It also won't open your eyes to the amounts of calories in your food. Counting calories seems to be a hassle for some, but at least you learn to judge your food intake. With a shake, that's just never going to happen. That's why you either have to live off of them forever (I guess, but good Gods, why would you?!), or learn better strategies eating the foods you like to eat. Same goes for juice fasts or any kind of restrictive diet. So, TL;DR: no, and no.

I have protein shakes 1 to 2 times a day. But the majority of my calories come from food. For me it's to get all my vitamins and minerals since I have never been able to get it from food alone. And because it's easy for breakfast and still healthy. I have never had any issues with my stomach or colon for that matter lol. But I'm also not eating only shakes. But they are also natural and no crap in them. I read all labels since I have quite a few food sensitivities. But to eat only smoothies I would die, how do you have snacks?

Constipation.

https://www.soylent.com/

Not for me. I'm still in a love affair with food in it's various tastes and textures. I just watch portions.

Try this; pickled beets and grated ginger that have Chia seeds soaked in the brine overnight, mixed with Greek Yogurt. Have it with warm Edamame bean pods and sourdough Wasa crackers.

Why bother losing weight only to gain it back again?
I will say that I am a big fan of a smoothie or shake as a meal in a long term plan of weight maintence. I am an 8 year maintainer and I have been mixing up protein shakes on a regular basis for a lot of that time. Especially on days when I am going out to dinner or want to indulge. I like to have one protein drink mid morning to keep me full and bank my lunch calories to save for a splurge.

I imagine there would be digestive issues. constipation or something. I am no scientist, I just FEEL like it is not a good idea to live on liquids only.

My aunt has cancer and for her, protein drinks are the only thing that tastes good to her right now. I understand doing this for true medical reasons such as chemo patients or the posters who had jaw surgery; for them this is their only true means of nutrition. I can't imagine a healthy adult wanting or needing to consume only protein drinks especially when you can eat fruits, veggies and other nutrient rich foods.

No you should be eating 90% real wholesome food