One type of duck is sweet and cold in nature(lighter feathered), and another type of duck is sweet and warm(darker feathered). The ones in supermarkets and restaurants are the darker one. Duck is used to provide nourishment for patients suffering from weakness, and the light feathered duck is especially good for yin-deficiency leading to flaring up of internal fire, asthma and lower back pain in the elderly. For duck to clear internal fire it shouldnt be roasted because this changes the nature of the meat and could make the condition worse. If you are suffering viral or bacterial infection or inflammation you should not eat duck as the meat causes the infection and inflammation to expand. Too reduce the bad reaction of duck meat, you can cook with ginger – and it will taste better as well.