I need more stats. Height, weight, age, activity level, % body fat?
PRIMAL IS NOT LOW CARB. We only think it's low carb because SAD is so freakin' high carb. The truly low carb people are meatitarians who eat no veggies whatsoever.
Eat sweet potatoes and your muscles will firm up again. If you start gaining fat, then you're eating more carbs than you need. Cut down on sweet potatoes. The End.
5'0" female, 44 years old. Started Primal October 31, 2011, at a skinny fat 111.5 lbs. Low weight: 99.5 lb on a fast. Gained back to 115(!) on SAD chocolate, potato chips, and stress. Currently keeping food tracker.
I (try to) follow by-the-book primal as advocated by Mark Sisson, except for whey powder and a bit of cream. I advocate a two-month strict adjustment for newbies. But everybody is different and should tweak Primal to their own needs.