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!