A prime example of this is how when certain people go on a crash diet and they seem to gain more weight despite drastically reducing their food intake. As mentioned before this is because the body figures out that it might be a while before it gets chance to process something for energy, so it then switches into a mode that makes it even more efficient at extracting even more out of what little food your body is being  given for energy to store. You can see how this trait might have been very useful and would have helped to increase survival amongst those who possessed it when food was more difficult to acquire in our early ancestral lineage. Meaning that the genetic expression was able to propagate itself more extensively via the process of natural selection.