Unhealthy can have two conditions. one condition is that it is harmful for body. other condition is that it is not useful but still has no benefit. if you mean harmful to body then yes anything harmful to body is Haram. 

There is a law in Fiqh that anything harmful to body is haram. But deciding if a specific substance is harmful for body or not it is not an Islamic matter. but it is a scientific matter that scientist and doctors should specify it. Islamic scholars only say the general law. 


**Reference:**

http://javab.net/hadavi/fa/questions/question/fa796