I imagine that ones metabolism factors in as well. I was sick once, couldn't eat anything for 14 days due to large wounds in my mouth. I felt fine if you factored out the pain.
Lost 8-10kg (I'm an athletic, not large person) and I could barely exit a car when I visited the doctors office. I remember being very tired, but not feverish, so I don't think that factored in.
Regained the weight extremely fast when I started eating again. I remember how that surprised me!
What really stuck out for me was just how much time I was spending each day either planning meals or eating them. Easily four hours a day, including cooking, cleaning, eating, and planning meals with friends.
The social part was not so big a deal for me, but only because there were four of us in our fraternity trying it all together. Plus, well, living in a fraternity and being in college. I didn't need the excuse of a meal to hang out with people.