I need to gain weight but i want it to be in muscle. i'm 5'7 and 96 pounds with a fast metabolism , how can i do this?

Dietician: Have you had your thyroid function checked to make sure that it is not overactive? If it's not then it's a simple matter of increasing calorie intake. I recommend that you have a consultation with a dietician at your hospital where you would get expert advice on what type of diet is healthy for you and your activity level and your ideal weight would be determined.

Eat & exercise.: You need to focus your exercise regimen more on weight training than aerobics. As well, make sure you eats lots of food, and focus on complex carbohydrates and lean protein sources.