I'm 40 years old, been eating low-carb for 18 months and Paleo/Primal for 10 months. My cycles were always long - 35 to 42 days - although the flow usually was only about 5 days. I've always had massive tension headaches two days before the flow starts and also in the middle of the cycle, plus water retention, cramping, increased hunger, lowered immunity (interesting someone else mentioned that too, I'd never heard of it anywhere else but definitely noticed it myself), joint aches, flu-like symptoms, and an attack of diarrhea the day before the flow started (funny someone else mentioned that one too, I only saw mention of that one other time. I read somewhere that it's from a hormonal surge just before your period starts - progesterone I think it was). All of that has gone away, and my cycles are now very consistently 28 days, flow for two days. Mostly symptom-free except for slight increased hunger. Most of the symptoms went away pretty quickly, within the first 6 months. I did go through a couple months when I spotted very slightly in the middle of the cycle, but that went away too. It took over a year for the cycle to reduce down to 28 days and for the headaches to go away completely.