Hi Thank you for asking HCM. I have gone through your query. Your problem can be due malabsorption syndrome or parasitic infestation. This can be ruled out by stool routine examination. Deworming should be done with antihelminthic drugs like albendazole. In case of malabsorption syndrome it should be treated also. Taking balanced and proteinaceous food will be helpful to gain mass. Milk and milk products, eggs, meat and chicken can be taken. You can also take protein supplements for mass gaining. You can also do mass gaining exercises. Hope this may help you. Let me know if anything not clear. Thanks.