Unless you didn't eat for 1.5-2 days before your flight, you can't really point the finger at UA....

That being said, United takes these complaints/feedback seriously. However, unless there are multiple accounts, there's nothing to indicate UA whatsoever.

EDIT: Just in case you didn't know: Taking activated charcoal and apple cider vinegar can assist with food poisoning. Both are available via amazon in the pill format. Source: a blog on boardingarea.com that i will google when I am able to.