I was pretty much vegetarian for a 6-week period one summer (by force--there wasn't any fridge space for meat and I was too squeamish to handle raw meat that year). My parents took me out for a steak dinner the night after that final. I was very unhappy that evening. I've never heard of it happening with grains, but I wonder if it's a matter of your digestive system going "Hang on! What is this?" if you haven't eaten it for a while.
My vegan best friend would have to start introducing small amounts of cheese into her diet a month before breaks because her mom thought she was just vegetarian...

I'm just a little suspicious of diets that revolve around the idea that some food group(s) are concentrated evil.

Anyway:
Dear BF:
Your girlfriend may have been gotten by the bodysnatchers. That is the only explanation for the fact that she bought running shorts last week and decided to clean all the things this week.
Sorry.