The ships I've worked on have 4 different 'venues'
Crew mess - where anyone can eat - usually geared towards whatever countries the majority of the crew come from, lots and lots of rice and soups, stews, curries, stir-frys. Usually Asian, Caribbean, Filipino tastes
Staff mess - where those considered 'staff' - cruise staff, shoppies, admin and pursers, show people, etc. More geared towards 'western' tastes - plainer meats, chicken, fish, rice, potatoes, soups, maybe a sandwich and salad bar
Officers mess - for those marine and hotel folks who wear at least a couple stripes. Usually a menu or what the pax are being served. Tablecloths and someone bussing the table
and the fourth is pax areas - you might have the privilege to eat in the dining room or specialty restaurants, staff who work late can often get into the 24 hour pizzerias or last 15 minutes of the midnight buffets.
but all in all - lots of food is available and you pretty much have a choice on how healthy you eat. I have loads of coworkers who are 'holistic' or vegan who eat quite well onboard. Can also depend on how active the crew welfare group onboard is in staying on the food and beverage department. My last ship there was a girl very proactive in getting steamed chicken and vegetables for lunch and dinner - and they started serving whole grain breads and brown rice.
And if there's a port day - lots of great restaurants around the world to choose from