Jaime from the Mythbusters does this; he explains it in an episode where they are testing fuel consumption of cars over a long distance and can't stop to eat. Adam brought snack foods, Jaime brought what he calls "444". 4 fruits, 4 vegetables, and 4 beans ground up in a blender for him to drink. He put his recipe in an email that someone posted to reddit at one point.

Jaime claims it's healthy and full nutrition, but he only eats/drinks it when he can't be bothered to actually eat something.

It bears repeating, over and over, that this is not how it was originally pitched. That is not the marketing at all.

It is being marketed as a total meal replacement. There is a thin bit of legalese to cover them in case some poor bastard will die of malnutrition.