Being lean is mostly good if you are healthy and have strength. But being underweight is a concern if it is due to poor nutrition and many other issues, being underweight you are at risk of developing anemia, fragile bones, hair loss, fertility issues, and nutrient deficient. You can check if you are underweight or not by using a BMI calculator. If you are finding it difficult to put on some good weight and by weight, I mostly refer to some muscles and good fat.
