How do you gain weight for an underweight person?

Answer 1

You probably have a very high metabolism which makes it hard to gain weight. I would slowly start to rasie your calories are start a weight training program. Make sure you are eating quality foods, and not just going out to fast food everyday to gain.

Answer 2

Healthy weight gain can be achieved through strength training and working out. Check your BMI to see if you should gain weight at all.