Hi lybrate-user you do maintain these (1) regular exercise like yoga, swimming, skipping, push ups, sit ups etc (2) eat more foods more often (3) drink milk or milk shake (4) use weight gainer nutritional supplement (5) eat more vegetables, fruits, lean meat, fish, egg. Cottage cheese etc (6) add cream, butter with food (7) banana 2-3 pcs (8) no water before or during meals (9) drink 3 lit water/day (10) no smoking and alcohol (11) avoid fast foods and junk foods, processed foods (12) take quality sleep (13) stay stress free. These will help you.