In theory, would it be possible to create an injection of Vitamins, Minerals, sugars etc so that eating was no longer necessary?
The quantity of nutrients the body requires takes much more physical space than can be included in a simple pill or injection (used only a few times a day).  But nutrition can be provided by IV (intravenous administration), and it is used today for some medical conditions.  When the IV completely substitutes for normal digestion, it is called total parenteral nutrition (or TPN).  The procedure is simple and reliable enough that it can sometimes be used outside of a hospital setting and be self-administered by users at home.