Biology is not a simple linear physical equation. We have buffers. There's a lot of balancing mechanisms inside and altering your food supply can change the state your body operates in. Or if I may try this naive comparison, when I drive my car and use brakes, I slow down up until a point the engine starts to reaccelerate. The ECU adapts to reallocate more energy because going too slow would "kill" the engine. For a computer, fasting would be like reaching memory pressure so high, your OS garbage collects/flush caches and then programs suddenly runs better.

ps: not that I like all of Levin's work, I do admit that his tendency to abstract into grand ideas is not helping, but I think the morphogenesis/gap-junctions part of his work is still very interesting and straightforward.