I think that in this arena there was no editorial consitency or thought on the matter and that it just depended on the writer. Most likely the conflict was just completely ignored with the assumption that no one would bother to think about it or would even notice it. Maggin's Superman was certainly no vegetarian and even helped his mother cook meat.
Much like those old Disney comics where Donald Duck and clan sit down to a nice family dinner of roast duck, where the implication is that the walking-and-talking main character ducks are completely distinct creatures from mere "animal" ducks; the beef in beef bourguignon was somehow never really "alive" or part of an animal.
Either that, or in Superman's code there's a difference between direct killing and indirectly supporting an industry.
Waid's solution of making Clark a vegetarian was a good effort in bringing consistency to the table, but it merely moved the problem. Is eating plant life "taking a life"? I suppose that Superman's code now only applies to beings with a certain level of sentience because, to some degree, everything is alive.
The real question is - does Kal require material sustenance? If so, then eating is a matter of survival. But if not, then eating is a conscious choice to kill something.
I've vowed to preserve ALL forms of life wherever possible.
That "wherever possible" bit might make things somewhat flexible.