句中的 with "negative consequences" for those affected and wider society 可以看作是 with 复合结构,for those affected and wider society 作补语。
However, there are fears BMI on its own is not a "reliable measure" of an individual's health and may be resulting in both under- and over-diagnosis of obesity, with "negative consequences" for those affected and wider society.
这句话的for those affected.....是做状语修饰前面的consequences吗?还是作定语?介词短语能后置做状语修饰前面的名词吗?