Hi and welcome to HCM. I want to clear some facts on weight and height Inheritance: It may be due to the genes.Parents or one of the parent has the nature of not gaining weight even though the person involves in any type of food habbits or regimen.So this will be inherited by the offspring also. Absorption: There may be some problem because of which the persons intestine may not be able to absorb the essential materials or end products of digestion which inturn results in malnourishment thus leading to underweight. Digestive problems: The individual may not be in the state of having enough food due to some causes like for eg- some get indigestion if they have even a little extra food,or may be suffering from irritable bowel syndrome,or colonitis or something like that.The person may not be involving with correct habbits or exercises to get the food digested well , assimilated and the good part of the end product of digestion to be absorbed to meet the body needs. Low Hb% in the body: If a person is aneamic also then wont gain weight.so boost up your Hb% Unkown cause: Here no matter what ever the person does,there is no problems of digestion absorption or malnourishment but the individual remains thin but active and healthy. Home Remedies for Weight Gain • Eat banana three time a day followed by milk of curd. You can also make the banana shake in milk to gain weight. • Eat lots of fruit with milk. • In summers you can drink mango shake in milk daily to gain weight If you have tried everything and not gaining weight, instead losing weight, its time to consult a doctor for proper diagnosis of reason behind this. Regards Dr Santosh