Healthy weight gain means more increase in muscles and to a certain extent fat in order to support those muscles. Just
eating anything or high calorie foods will result in only fat gain which will not give you a proper body shape and will also be detrimental later in life. In order to achieve a healthy weight you should know what you have to eat and how much to eat. I have 11 years of experience in this field and have helped innumerable people to manage their weight.