There were two special trees in Gan Eden. In the case of the tree of knowledge of good and bad, we know that eating from it once produced a permanent effect. Was this true for the tree of life too, or was that more like a "maintenance" tree that you had to keep eating from to live forever?
The reason I ask is that initially Adam and Chava were permitted to eat from that tree. Once they ate from the other, they were prevented from doing so. So either eating from the tree of life would also produce a permanent effect and it's just "luck" (as if there's any such thing in torah) that they didn't, or that tree works differently, like regular food where eating produces a temporary effect and eventually you need more. (Or, I suppose, that it produces a permanent effect that is cancelled by eating from the other tree.)
I searched this site and reviewed Rashi on B'reishit and my go-to source for English-language midrash, Sefer Ha-Aggadah, all without luck.