I don't know if 20 days without food is healthy but, historically at this time of year, we would pretty much be fasting. We would have carb loaded at the end of summer and most of our energy would come from that stored fat since food would be scarce during the winter (little bit of greens and whatever meat we could get our hands on). Modern ways of eating/gorging are but a speck on the evolutionary timeline. What if you live in the tropics? Did I just blow your mind?