I did this this few years ago (TATL economy) when I was on a low-carb diet and it was a mistake. I basically got a low-fat meal with fruit and diabetic jam and artificial sweeter. Looking at the other meals being served, I noticed that could have picked around the "normal" meals.

More recenly, (no longer on a LC diet) I ordered a Kosher meal with while travelling CE and got sliced turkey and salad. This was a mid-morning departure, though. On the way back (5pm?) it was rice, salmon and veggies.