Hello dear Understand your concern Weight gain will depend on the your genetic factor and your metabolism. Sometime low weight also run in the family. My advice you to do not take protein power for weight gain as all these powder available in the market contain the steroid supplements. And steroid can cause weight gain but steroid cause lots of serious side effects like kidney damage, osteopenia, skin damage and decrease immunity lead to increased chance of infection. I give following advice you to increase the weight: Do regular exercise like walking, weight lifting, running, swimming and cycling that help in boosting up your metabolism. Take high protein diet like egg, meat, chicken, peanuts and ground nuts. Take fruits like banana, orange and apple. Green leafy vegetables daily. Drink plenty of waters 2-3 liters per day It will take time but gradually your weight will gain. Sometime weight will not increase due to genetic background. But avoid to take protein powder. Also go for testing thyroid hormones to identifies hyperthyroid problem as it cause in weight gain. Also rule out the worm infections by stool tests. Hope this may help you Best regards Dr. Sagar