I'm confused why the use of "increases" in the following sentence is incorrect --- I intuitively think it should be "increase" instead, but can't quite explain why I think so.
High consumption of trans fat is dangerous: not only does it increases your LDL cholesterol level, it also decreases your HDL cholesterol.
My confusion is exacerbated by the fact that "high consumption of trans fat is dangerous: it increases your LDL cholesterol level" seems grammatically correct, and the use of "decreases" in the sentence above also seems correct.