I looked through the entire book and cant find sour cream mentioned anywhere. I would think maybe in phase 2, if it was fat free and you replaced it with maybe a pat of the butter or the mayo. But thats my opinion, I wish the book had more details.
This would be an eat at your own risk item since measure for measure it is much more dense in calories than skim milk & you'd have to start figuring calories if you're going to sub it for your daily dairy allottment. Takes the ease out of the plan.
Skim milk is around 90 calories a cup. Fat free sour cream (which I cannot eat - yuck) is 200+ calories for a cup. I realize most wouldn't eat that much but that's a big difference & I'm not sure what other ingredients it has that might be different than skim milk. Detox is to eat as pure as possible.