Without knowing more specifics about your friend, I cannot pinpoint what the exact cause could be. Things in general that contribute to water retention include eating foods high in sodium and not enough potassium (which most ingredients in a NutriBlast would be low sodium, high potassium), being dehydrated (when the body is lacking water, it holds onto it more easily), a congested lymphatic system, compromised kidney function, certain medications, inflammation in the body, certain foods (see this article here:
http://www.nutriliving.com/blog/feeling-bloated), food allergies, or hormonal imbalances among others.
My suggestion would be to keep track of the ingredients in the NutriBlasts and switch them up one at a time to see if there's a particular food that might be the cause.
Regarding the weight gain...please read this article here for some tips: