Depends on the loading. For F, you are virtually guaranteed seconds if you want - they significantly overstock entrees. I sometimes order two "entrees" (usually a Chinese thing, which comes with a lot of accompanying dishes, plus a western main). Although if the cabin is full (9/9 or 6/6) you may not get a second of the exact entree you want, it is a virtual lock that they will still have seconds of some of the others. Plus many of the appetizers, soups and snacks are rather large - you can easily do a salad and a soup and count that as a meal.

For J class, it is more load dependent but they're not as overstocked as much as F. If F overstocks 200% (2 meals for every pax) J might be 110%. Just ask. Won't hurt.