See, it is myth that if you eat lots of food you will put on weight because it depends on quality to food rather than quantity of food.There are many reason of being underweight. 1. Endocrine disturbances 2. Genetic 3. Vitamins and minerals deficiency 4. Psychological problem 5.IBS 6. Eating disorder 7. Liver dysfunction And many more We treat the diseases by treating the cause of  disease.   So my opinion is to contact directly to us so that we can find the cause of weight reduction , gathering all your data and according ly we will suggest you.