1. How does diet soda cause to spike your blood sugar?
2. How does diet soda cause you spike your blood sugar?
Please comment on the above two questions.
Are both OK? or Which one do you consider OK?

 

Neither of these is correct grammatically. You need
"How does diet soda cause your blood sugar (level) to spike?"

(I doubt it's correct medically either!)

 

It is medically incorrect, but not quite as incorrect as I would have imagined. New research shows that diet sodas can marginally raise blood sugar by affecting the micro-organisms in the stomach.

But "spike" seems like a stretch to me. I think "How does diet soda raise your blood sugar" would be more accurate (but probably sell fewer newspapers).

Could Artificial Sweeteners Raise Your Blood Sugar?

[after drinking diet soda for a week] By the end of the week, blood sugar levels had risen in four of the seven people. Transfers of feces from people whose blood sugar rose increased blood sugar in mice, more evidence that the artificial sweetener had changed the gut bacteria.