I went without food for around 24 day, a few years back, most of it lying down in a hospital bed and not exerting any energy moving or keeping warm, which probably helped, having what turned out to be, a gangrenous appendics and being asked to choose a lunch and dinner daily ( just incase they decided to let me eat later) definitely didn't. .
The going without food wasn't the worst, the lack of water, being allowed less than a small plastic cups worth a day, for around a week, was far worse, despite that I was being kept hydrated via a saline drip. Ever since I feel uncomfortable if I don't have at least .5lt of drinkable liquid on me at all times.