United has invested quite a bit in their “Polaris” international premium cabin experience, in terms of food, wine, and amenities. However, it looks like the investments in their premium cabin product don’t apply across the board, as United has introduced some cuts to their domestic catering as of September 1, 2017.
As far as the big three US airlines go, United is the most detailed in showing customers what they can expect to eat onboard. The North America premium cabin dining page on united.com has a lot of information about what they’ll serve onboard based on how long your flight is, when you depart, etc.

FlyerTalk member qukslvr619 notes that United quietly introduced catering changes as of yesterday:
Flights 2:30-2:59 hrs:
Breakfast: Remove breakfast breads only
Lunch: Two cold meal options and a chocolate truffle (vs one hot and one cold option, mixed nuts/bread//side)
Dinner: One hot meal/one cold meal option (vs two hot options); offers mixed nuts/bread/salad/dessertFlights 3:00-3:59
Breakfast/Lunch: No change
Dinner: One hot meal/one cold meal option (vs two hot options); offers mixed nuts/bread/salad/dessertFlights 4:00-5:24 (exc. transcons)
Breakfast, lunch and dinner have cold and hot meal options (vs two hot-meals)
Pre-plated dessert replaces ice cream/sorbet on lunch/dinner flights
On top of that, United will no longer have real food on domestic redeyes, with the exception of their premium transcons. All other flights will just have a snack basket in first class.

Ultimately these changes are fairly minor, though I think it’s always interesting to see the direction that airlines take with their premium cabin catering. In this case, all domestic flights with the exception of premium transcons will feature at most one hot option, compared to the two that were previously offered in many markets.
Then again, given the quality of food domestically nowadays, I almost prefer cold options, since they’re a safer bet.
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