I think the people who assume that fasting for 1-4 days qualifies you for an eating disorder are a bit ignorant. Yes, people with eating disorders "fast" but it stems from a different place. It's also characterized by repetition of "fasting" as opposed to a yearly/bi-annual fast or something. As Miriel has said, many people fast (whether it's one meal, or a few days) for religious purposes. It doesn't hurt them.

Agreed with Miriel again, though, when I think that doing it for weight loss/health is not beneficial. Because, as she said, you tend to over-eat and your body stores up what you consume more, as you've been "starving" yourself. Juice fasts might be okay? But your body is still keeping some nutrients, and those are generally used more as detox anyways, not for weight loss (or how they should be used).