THe myth is that 12 weeks is the acceptable max, before your heart explodes I guess. SO says most of the literature, not the heart exploding part, the 12 weeks part. I'm not sure of the exacts but I imagine the body gets really stressed if it goes this long in ketosis, and the foods are all fat and cholesterol. In moderation CKD seems fine, 2 times a year maybe, but I dont think its healthy past 12 weeks.