I wonder if that's the case for low-cal or low-fat meals in coach too?

I've never ordered a special meal on an eastbound to LHR, but I always pack a protein bar for breakfast in Y because those greasy little hot croissants seem like they'd turn into instant love handles. (And by that stage of the flight, if I didn't have an alternative I'd probably cave and eat it anyway. Not a good way to start a jet-lagged day..)