We completed a Whole30 in January, 2011. If you vary your diet, include LOTS of fresh veggies, a little fruit and good quality protein you will not turn into a fatty.
Most of your plate should be vegetables. We try to have at least two veggies sides with our protein. We lost weight, but would have lost more if we would have restricted fruits/nuts. All of the nutrients in fruits are also available in vegetables without all of the sugar.
We each lost 15 lbs and have continued losing with continuing paleo the past 7 months. We screw up occasionally with beer (we live in Portland, back up off my beer cave people,) corn and dairy.
Total weight loss for me (Kylie) is 23 lbs, the bigger change has been my body composition.