Weight matters when you have a lung disease. Overweight may impact your breathing. If you weigh too little, it may complicate your recovery after diseases such as pneumonia or other infections. You will have to find a suitable balance.
However, when you have a chronic lung disease like pulmonary alveolar proteinosis (PAP) it is better to weigh a little too much than being too thin. This is due to the fact that if you get sick or have to be hospitalised you may lose weight. Regardless of your current weight position, you should always talk to your doctor before changing your diet.
In contrast to some diseases your diet has no influence on the progress of your disease. However, a healthy diet may influence your overall wellbeing in a positive way.
If you think you need to lose or gain weight you can discuss this with your doctor. He/she may be able to direct you to a dietician, in case you need to make any changes to your diet. You can also discuss the impact of your weight and diet in relation to your disease if you feel you need advice in this regard.