The perceived wisdom (mainly from the internet) is that for RNY patients, caffeine (the main constituent of Pro Plus) is a no-no.
1) It is claimed to cause ulcers.
2). It is claimed to interfere with absorption of Iron
3) It is claimed to interfere with the absorption of Calcium.
4) Caffeine is a diuretic. Early, post op, when you are fluids only, it can dehydrate you.
I am not a doctor, so I have no medical basis for these observations, and can only relay others opinions.
HTH
Chris