In 1954, similar blended fruit and vegetable drink recipes were published in a book titled "Nutrition For Health"  by Alice Chase, M.D.

Green Smoothie History

These are some examples of very early green smoothie recipes from 1940,  just two years after the introduction of the Waring Blendor which was the first modern electric blender on the market.

In 1955, similar blended recipes called Sunshine Cocktails were included in a book titled "New Guide to Intelligent Reducing" by G. Hauser.

The recipes above were also included in a book titled "Electric Blender Recipes" by Mabel Stegner published in 1952.