Hi For weight gain you will have to maintain proper nutritional supplementation to body through diet and also start doing muscle or weight training to gain muscle mass. You need to eat a blend of carbohydrates, proteins and fats. Add whole grains, rice, potatoes, sweet potatoes, ghee [in limits] and also paneer, tofu, eggs [if non vegetarian] and nuts in diet. Do not simply push on fats to gain weight. For weight gain a balanced diet is needed along with proper weight training exercises. Start weight training sessions under supervision of a trained physical trainer. Take proper sleep and drink plenty of water. You can also be advised protein supplements but take only under supervision of a dietician and in calculated doses. Along with it, avoid stress and do not be over anxious as weight gain takes time if you do it in an appropriate and healthy way. Also, once get a full body blood workup done. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Honey Arora, Dentist