Hello dear, we normally plan a diet in such a manner that it not only help in increase weight but also increase your appetite. See, there is cause behind any disease. Underweight also caused due to many reasons like 1. Endocrine disturbances 2. Genetic 3. Vitamins and minerals deficiency 4. Psychological problem 5.IBS 6. Eating disorder 7. Liver dysfunction And many more   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.