Pre op diet

 I am having a hard time staying on the pre op diet. The sugar free Carnation Breakfast drink tastes very good but it upsets my bowels. I don't know if it's the sugar free or the milk. Did anyone else have this problem? Thanks for you help.

Can you switch to a soy protein drink and soy milk or mix it with a lactose free milk.   I can't drink milk so I have to mix all my protein with soy milk. 

 Thanks,
I started using soy and I feel a lot better.