gain weight and gain muscle, aka tone up :) i used to be skinny fat too but now that i've started exercising and eating better i'm looking so much better
Eat more food, including plenty of protein and healthy fats and lift heavy weights!
This. Especially if you've been undereating, stay off the scale for a little bit, since water retention will show up immediately and for some people, that can scare them away from finally eating enough.
1. If it happens so suddenly, most of it is water weight, not fat.
2. Aren't you battling anorexia? Your body could use those 10 pounds, if not more.
3. This is your ED talking.
I would second Tina's post, but, depending on how low your weight is, heavy lifting might not be for you just yet.