Fat guy in a blubber coat! And to answer your question, those people could survive a month long prison sentence without being fed... They have enough energy stored in their tissue to detonate a thermonuclear bomb. So the answer is never. How often do you need to eat? At least once every three or so days. Ideally you'd just be skipping eating one day of every four days. Studies show you will live up to 15% longer and with much better quality.