Are there any reports or research on severe headaches experienced by people following the South Beach Diet?

My 49 year old sister lost 35 pounds following the South Beach Diet, and has stayed at a weight of 110 pounds since she began the diet over four years ago. She was just hopitalized for three days due to an excruciating headache. She had to be heavily sedated with Demerol she was in so much pain. An MRI & contrast CAT Scan found nothing abnormal. Finally, her doctor gave her an injection of some kind of medication in her neck to block the pain and she was released from the hospital. I recently heard a radio report by a well known nutritionist (Gary Null) who stated that he believes the Atkins Diet -- and similar high protein low carb diets -- have very serious negative long term health consequences. Headaches was one of the many problems he mentioned. A quick search using Google did yield some articles on this subject, but I'm wondering if anyone can comment on their own experience or maybe point to additional research.