My periods were wacky the first few months on Atkins (April-August) and yes, I skipped one period, had breakthrough bleeding 2x, one period was so bad I thought I was dying - heavy cramping, bleeding, you name it!! Last 2 months I have regulated somewhat - - my periods are on time, they last a normal 4 days, and yes, I do have some nasty cramping but MIDOL helps.