CaseOne (not her real name) was a lady of about 50 years, who had suffered from migraines about twice a month for about 15 years. They would last for three days, and were very painful.
She tried to work out what was causing her migraines, but there seemed to be no particular triggers. They just happened when they happened.
One afternoon, she got another migraine, and when asked what she had eaten, she said "I only drank two glasses of (cloudy) apple juice because I was thirsty."
Now, this seemed quite remarkable. What could it be about apple juice that would trigger a migraine? "Tannin" came to mind. (It is a natural chemical that makes the brown colour in apple juice.) Tannin also occurs in red wine, and red wine is a well-known trigger of migraines. Aha!
So CaseOne looked at what else she was eating that contained tannins. Tea, chocolate, and alcoholic drinks that are matured in the barrel seemed to be the significant items. So she stopped eating and drinking these, and she got far less migraines.
She still got some migraines, but it now became much clearer what were causing them. One example was a drink called "wild blackberry." Another particularly bad example was carob, which some authorities claim is a good substitute for chocolate for people who get migraines.
CaseOne missed her tea, so she tried drinking one cup of weak tea a day. But sometimes, until she learned to be very careful, she would take too much tannin, and trigger a migraine.
Now, CaseOne is free of migraines, and hardly notices the change in her diet.