All major lines can accommodate special requests, but some lines have larger programs than others. SeaDream Yacht Club, for instance, is the only cruise line with an optional raw food menu. Regent Seven Seas Cruises and Oceania Cruises offer vegetarian dishes and a vegan menu with breakfast, lunch, and dinner, and even afternoon tea. Costa Cruises has a gluten-free menu in the main dining room for three meals a day, and on Carnival Cruise Line, you'll find gluten-free bread, baked goods, pizza, and even beer. Disney Cruise Line also does a great job meeting dietary needs for families.

Many lines have sample menus on their websites to give you a sense of what is offered in each of the restaurants. Although there's no guarantee what you see will be the exact dishes when you cruise, you will get a good sense of what the standard mix of offerings will be. See if there are a variety of vegetarian and vegan items. Gluten-free dishes may also be marked with icons, as is the case with Celebrity Cruises and Royal Caribbean.

Even with all of the menu options available, you should always let the cruise line know in advance if you have dietary requirements beyond just being a vegetarian. Most lines require that you fill out a special form detailing your needs, and request the information 30 to 90 days before your cruise. 

Meet with the restaurant manager on the first night to be sure the kitchen staff is aware of your requirements.Don't be shy: The manager can also go straight to the chef to fulfill additional special requests — but don't delay because this usually requires 24-hour notice. There are typically some standard meat- and dairy-free dishes in the kitchen's repertoire, such as vegetarian curries, tofu stir-fry, and other Asian dishes.

Head to the salad bar and get creative with your concoctions. In addition to fresh vegetables, you'll often find legumes, olives, and fresh fruit, and sometimes quinoa, hummus, and a grain dish, such as tabbouleh. Another area at the buffet that tends to have vegan and vegetarian options is the international foods section, where there may be a chef cooking stir-fry to order. 

If there is a gluten-free section at the buffet, vegans and vegetarians should also head there, as it's where cruise lines tend to stick other healthy options, such as kale salad — even at the breakfast buffet on Holland America's new Koningsdam. People with gluten allergies know buffets can also be hazardous due to cross-contamination. When in doubt, ask the staff if they can bring you items straight from the kitchen.

Detox drinks are in vogue on cruise ships. For instance, for a fee, you can order fresh blends at the juice bar at the Senses Spa & Salon on Disney Dream or at the Asian-inspired Aurea Spa on MSC Divina. SeaDream's juice bar is complimentary, serving up blends like a Blood Apple Blaster (apple, ginger, red beet, lime juice, and agave). If you'd rather your treat be a little sweeter, ship ice cream counters have sorbet and sometimes other dairy-free choices.

The annual Holistic Holiday at Sea cruise was developed for vegan travelers. The group even brings its own chef, who creates special menus in advance. (There are also yoga classes on deck and lectures on healthy living.) The next trip is a seven-day Caribbean cruise on MSC Divina in March 2017.