It's interesting, there's a lot of research on this topic. I suppose it's all done by men trying to get rid of PMS symptoms in women. Funny how much research was done on Viagara issues too <img src="/images/graemlins/smile.gif" alt="" />
In any case, they found it's not that we're missing something nutritional, a la people who eat dirt because they're low on iron. It's about hormone levels in our brains. Just before our periods, we dip low on serotonin. Now, carbs boost that back up - but if you go for the high-sugar carbs (a la chocolate) you set yourself up for a roller coaster cycle. You get a big boost, then a killer trough when they zip through your system. Then you want more. So you sit there eating an entire box of Oreos <img src="/images/graemlins/smile.gif" alt="" />
The saner way to fight PMS is with a slower, even supply of carbs so that your body gets the serotonin equalizing it needs without the insanity. So whole grains that digest evenly.
Also research shows that having ample calcium in your diet really helps with PMS. So people who say have a box of brownies and milk - or a container of chocolate ice cream - might actually be partially trying to fix their calcium craving.
Something to consider!