I can simply not tolerate buckwheat, as I found out recently when I decided to try some buckwheat pasta. The following day I felt just awful, and finally violently threw up after hours of feeling miserable.
I didn't realise it was the buckwheat though . . . and after eating a smaller amount of pasta a few nights later, I had to be sent home from work the following day. Oops!
Not sure why it should have caused such a wild reaction, but if you're trying new foods, I'd recommend trying just a little bit to begin with to make sure your body can tolerate it without any problems.