High gloucose reading while on the pre-op diet

Has anyone else experinced high levels while on the pre-op diet?  My  levels were good (below 100) prior to going on the pre-op now they have been shooting up to 200.  I have sometimes had this happen before when I am not eating enough.  Any thoughts would be appreciated.

What does your pre-op diet include? All surgeons have different (or even no) pre-op plans. Are you on clear liquids, protein shakes, protein and veggies...?

I am on 3 Shakes a day plus one small meal

Are the shakes low carb? If not this could be the problem.