This question has come up a few times over the years. Whether it was asked in jest or if a person were really considering living on smoothies in an attempt to lose a lot of weight quickly, the question is valid.
So, can you? There are varying opinions and there are also variables when talking about what kinds of smoothies. If we define smoothies as nothing but juices of fruit and vegetables then a person could probably sustain themselves on them for a while but couldn’t live long term on them. Even though they could get protein from avocado and nuts, the amount of protein needed would have to be supplemented by adding an extra source of protein to hit the required daily protein intake of 56 grams for men and 46 grams for women.
If your smoothies were complex and the amount of nutrients and proteins were measured correctly and supplemented when needed, you could feasibly live on smoothies indefinitely. You can balance smoothie and solid food intake to lose weight by targeting calorie levels 10-20 % lower than the recommended daily intake for men (about 2500 calories) and women (about 2000).
Calorie restriction is probably the most healthy and consistent way to drop pounds if done in the right amount and making sure one gets the proper nutrients along the way.
There are those people who cannot eat solid foods and liquidified food may be there only option. Smoothies offer a great way to take in calories and vitamins in liquid form.
So, in conclusion, the answer is yes you could live on smoothies if you took in the correct amount of vitamins, nutrients and proteins. You will need roughage too to make sure to stay regular.