Some people though they're thin at the beginning later they were able to add themselves more weight than I expected to see in them! and some didn't change much and almost look the same to me when compared to before they begin their diet plan!
Protein doesn't help you to gain weight as much as fat can do... I think it all depends on the amount of calories you're having daily. Simple rule 1gm of protein = 4Kcal 1gm of Carbohydrate = 4Kcal 1gm of fat = 9Kcal