Somehow, for a lot of girls, it seems like weight gain is a no brainer once we are healthy again...it sort of follows us around and jumps us when we are not looking...
But a lot of guys complain that they can't seem to get back to a healthy weight and that they look too skinny or undernourished.
For the guys you need a two pronged plan of attack...firstly nutrition...High protein diet with extra protein to build muscle, healthy fats (nut butters, coconut oil, olive oil...) and good proteins supplemented with protein powders.
Whole grain breads, oatmeal and other full grain sources of carbs are good too.
Then you need to train with weights to help to build your muscle mass...you do not need hugely heavy weights but slow movements and pyramidal training.
It is the forever guy/girl thing...we want less, you want more.
Good luck.
Sharon