I suppose if the alien race had underdeveloped biotechnology in comparison to us, then they would have to find some other way of getting food. (Assuming that they eat food, and they eat organic food.) The beforementioned scenario of the aliens facing many hostile beasts on their own planet, may mean that the organisms they need for food are annoying to gather.

To compensate, they mine essential minerals and other things from the ground. Using these pure minerals, they make a pure cocktail of sustenance which they take swigs from every so often. Sort of like a multivitamin for everything.