My girlfriend had no problem eating the greasiest of foods up until recently, where her stomach suddenly now cannot tolerate oil/fat, and also cannot tolerate cold water (must drink warm-hot water.)
What type of gastrointestinal issue is this?
Does she still have her gall bladder?
patients with upper abdominal pain and who conform to a profile of ‘fair, fat, female, fertile and forty’ are likely to have cholelithiasis.
(reported for being in wrong forum)
Yes, she still has the gall bladder.
She is in her 20s, not 40s, and slim.
Detail I should have added: She grew up abroad (and her gut was just fine then,) but only after coming to America, and especially, after a recent vacation to Georgia, did her stomach suddenly become extremely sensitive to fat and other things.
Could it just be a case of heartburn? Maybe try taking some antacids when it flares up and see if that calms it down.
Otherwise, my guess was the same as Kayakers (even though she’s not fat or forty).
In any case, if you want some internet strangers to diagnose her, we’d need some symptoms beyond suddenly not tolerating fat or cold water.
Does she go to another school? 
You wouldn’t know her.
This is just a real WAG, so please take it as such, but your mention of her experiencing the issue after a vacation to Georgia made me think of Alpha-gal syndrome, an allergy to meats like beef, pork and lamb transmitted by the Lone Star tick. GA is well within their range, and those meats often are oily / fatty, so maybe it’s the meat, not the greasiness that’s affecting her. The cold liquid thing, I don’t know, maybe that’s unrelated.
Or again, maybe I’m waaay off the mark. Does she get any of the other symptoms listed in this article?
Since this involves a real world medical issue, let’s move it to IMHO (from FQ).
May be the crap we put in the food here. My son has IBS or Crohn’sor otherwise stomach issues. We went to Greece for a week and he ate regular food there, drank beer and never had a stomach issue at all.
I wonder if the OP’s reference is to the country Georgia and not the US state?
And my WAG, if it’s the country Georgia, would be a H. Pylori infection, which is more prevalent there than in the US. Or she could have picked it up as a child abroad and it was just dormant until now.
I had just heard about this syndrome for the first time, a few weeks ago, while listening to a documentary on NPR. Doctors were telling patients, “No one develops an allergy to meat late in life,” until they learned about this syndrome.
This was my thought as well. According to this article on food additives that are banned in Europe but allowed in the U.S., BHA and BHT are used as preservatives for foods that contain oils or fats. This same article mentions that the additives have caused stomach problems (cancer, to be specific) in rats.
Heh, you did get me wondering for a minute if I, as a naive provincial American, just assumed Georgia the U.S. state erroneously, since the OP did say their girlfriend grew up abroad. But the wording of this passage sounds like they did mean GA the state:
I noticed an upswing in digestive issues with fast food when they started screwing around with ingredients - for the most part I can’t do any fast food any longer. Palm shortening [many people are unable to do palm oils and it has been the miracle/cheap shortening. I can’t even do freaking doughnuts most places now] mushroom powder [mushroom allergy is also very common, and it is generally the ‘natural flavoring’ that is umami boosting savory foods] shellfish [‘oriental flavor’ oriental fish sauce is whatever is dredged out of the ocean, frequently shellfish so not just oyster sauce can have shellfish in it.]
And don’t discount the actual oils as well, many people have a nasty digestive reaction to canola oil, we generally no longer use corn or soy as the cheap oil.
@solost, true, from the wording you quoted it could be the state; the “grew up abroad” had me thinking of an overseas vacation.
We could ask the OP:
@Velocity, was your gf’s vacation in GA the US state, where she may have been bitten by a Lone Star tick and developed Alpha-gal syndrome? Or Georgia in Eastern Europe, where she could have been infected with H. pylori?
Of course there are many other possible diagnoses.
Except for lupus. It’s never lupus.
Peptic ulcer?
Georgia, Atlanta specifically.