I asked my doctor once if there was such a thing as dog food for humans because I saw an episode of futurerama where they were advertising "bachelor chow" and it piqued my interest. I wanted to find a single food source that I could stock up on that would give me all the nutrition I would ever need with out lacking in any one category. He laughed so hard at that, and then got serious and said ensure it probably the closest thing. He told me they feed people in comas via feeding tubes with something that is basically the same as ensure. It is formulated with all the vitamins, minerals, fat, proteins, glucose and etc that an average person needs. You could basically live off the stuff if you drank the right volume per day to meet your caloric needs.
So yeah, I think you would be fine on ensure. Probably not even lose any weight if you drank enough to satisfy your caloric needs.