Hello, Thank you for writing to HCM, Masturbation is for satisfy yourself sexually when you dont have any partner. But its good if use in some manners like no excessiveness. Its a thing which people follow by their own way because people follow in what they are having more sexually satisfaction. But excessiveness might occurs problem for the same like weakness and more. You should definitely go for it but not to be so excessive. Now if we talk about underweight than it might not because of masturbation but you may have to take some food which gives you more protein, that could be the solution of underweight. Still if you had any queries you may concern a good doctor for more help they may suggest you better. Hope you will find it helpful. Thanks & Regards, Dr. Gaurav Prajapati