Suggest a cruise vacation to a fitness buff, and you're apt to get a negative response. Sure, most lines have added aerobics classes and exercise equipment to their ships, and shore excursions now include active options such as white-water rafting, diving and mountain biking. But what about the food? A dozen feedings a day, a parade of killer desserts, and that ominous midnight buffet . . . As one quipster put it: "Afloat you bloat." Not in the '90s. Responding to demand from health-conscious repeat passengers, and trying to attract a new clientele among younger vacationers, the cruise industry has lightened up its menus while beefing up athletic activities. Salad bars have become standard luncheon fare on the buffet deck. Vegetarian entrees and simply broiled chicken and fish dishes have joined the mix of red meats in the main dining room. Menus proliferate with asterisks denoting appetizers, entrees and desserts that are low in calories, sodium and cholesterol. Even the dreaded midnight buffet has shaped up, with fresh fruits, light pasta dishes and other guilt-free items sharing space with lobster Newburg, beef stroganoff and crepes suzette. "In the last few years, I'd say nearly 100 percent of cruise ships have changed their meals and menus to accommodate passengers who want lighter, healthier fare," says Jim Godsman, president of Cruise Lines International Association, an industry group representing 32 cruise lines that account for 120 ships -- 97 percent of the business sold in the United State and Canada. Jennifer De La Cruz, a spokeswoman for Carnival Cruises, one of the largest fleets, with eight ships, says a recent study by her company's food and beverage department found a 300 percent increase in consumption of vegetarian entrees over the past few years, a 20 percent increase in seafood and poultry orders, and a 20 percent decrease in interest in red meat. Julie Benson, of Princess Cruises, says drinking habits have followed eating patterns onto the health bandwagon. "Sales of mineral waters have zoomed on our ships," she says. Those who want to eat and drink to the hilt can still do so on most ships -- and many passengers still see huge amounts of rich goodies throughout the day as an essential part of the cruise experience. But cruise lines report that a growing number of passengers are after quality rather than quantity and don't want to be confronted with food-laden tables -- heralded continuously over the ship's loudspeaker system -- every time they turn a corner. "We actually had people thank us for not having a midnight buffet, saying it's one more temptation they don't need," says Robin Lindsay, a vice president with 2-year-old Diamond Cruises, which operates the Radisson Diamond. He added that the Diamond's dinner menu always included a selection of healthful choices, including vegetarian entrees, grilled fish and chicken dishes, and low-calorie pastas. Ann Burguieres of Regency Cruises says ordering of diet-conscious items soared when her company created a separate Lean and Light dinner menu, with each course labeled with counts for calories, sodium and cholesterol. The line also has a Lean and Light buffet at lunch, with salads, fresh fruits and high-fiber granola and breads. People appreciate not having to navigate past all the fattening temptations to find something healthful, she says. The degree of food consciousness-raising on board varies from one cruise line to another, ranging from a few low-fat items flagged on the dinner menu to dining rooms devoted exclusively to healthful eating. The most ambitious program -- at a price -- debuted in May aboard Cunard's Queen Elizabeth II. Passengers on trans-Atlantic crossings can book a $599 Spa World Health and Fitness Package, that not only entitles them to the run of the ship's 6,000 square feet of exercise facilities, abundant spa treatments and lectures on nutrition and stress reduction, but also gets them a seat in a dining room where only food low in calories, sodium and fat is served. The package can be bought only by passengers booking first-class "Columbia-grade" cabins, and once you commit to the Spa World dining room, you can't switch back and forth to the regular restaurant. Traveling companions who want to dine with package participants in the Spa World restaurant but don't want spa food can order off the menu of the adjacent Columbia Restaurant. Passengers who don't book the Spa World package can still refer to specially marked menu items in the ship's other dining rooms. Here are a selection of other cruise lines with healthful eating options. (The lines also have extensive on-board fitness facilities). Ask your travel agent for more details. Be aware, however, that just because a ship caters to healthful eating doesn't mean you're off the hook willpower-wise. Norwegian Cruise Line, which offers lean dinner entrees, lunch-time salad bars and even fresh fruit platters at its midnight spread, recently introduced a new buffet sure to tempt even the most intrepid dieter -- an afternoon Chocaholics' Bar. "It's all things chocolate, and it's really sinful," promised an NCL telephone reservations agent, who then giggled: "And guess what, it's just down from the fitness room!" * Royal Cruise Line. All cabins contain a 14-page booklet titled 'Dine to Your Heart's Content," which gives tips on healthful eating on board, based on American Heart Association guidelines. The publication provides fat, salt and cholesterol counts for selected foods and sample plans for daily dining afloat -- which are reinforced by flagged items on the restaurant menu. A separate breakfast menu contains items such as fat-free pancakes and egg-white omelets. A lecture program called New Beginnings brings on experts in nutrition, fitness, stress and other quality-of-life issues. They give scheduled talks as well as informal one-on-one consultations. * Royal Caribbean Cruise Line. The line's Shipshape health and exercise program includes Shipshape menu items for each dinner course. There's also a separate vegetarian lunch and dinner menu, which, though not made up entirely of low-cal items, always includes a sampling of healthful choices. The shipboard menus were created in consultation with an in-house dietitian formerly with the California's Pritikin Longevity Center. * Carnival Cruise Lines. Spa cuisine is identified on menus, and extensive salad bars with low-cal dressings are offered at lunch on all ships. The line has added vegetarian entrees, and ship-board chefs have been experimenting with fresh herb and spice seasonings. * Windstar Cruises. The line recently hired Joachim Splichal, chef-proprietor of several of Los Angeles' toniest bistros, to create 180 new menu items, designed to be gourmet-light. The menu relies heavily on fresh market produce from ports of call, and recipes often use spices in lieu of heavy sauces. Chef Splichal helped produce the spa cuisine for Canyon Ranch, one of the United States' best health and fitness resorts. No midnight buffet. * Holland America Line. A full-service juice bar attached to the huge Ocean Spa on the Statendam, Maasdam and new Ryndam offers fruit and vegetable juices, plus a variety of bottled waters. All menus include flagged heart-healthy selections. * World Explorer Cruises. The line offers a wide selection of vegetarian entrees and salad choices, and no MSG is used in food preparation. Low-cal and low-sodium foods are flagged on menu. Midnight buffet is a light snack. On-board Passport to Fitness program instructors can help passengers devise a plan for healthful eating afloat. * Princess Cruises. Light cuisine choices are offered at all meals, as well as extensive salad-bar selections at lunch. Midnight buffet is more of a snack than a spread. On-board Cruisersize fitness program instructors can give tips on healthful eating as well. * Crystal Cruises. Menu at lunch and dinner highlights a healthy full-course meal. In addition, guests can order an abundance of items on and off the menu at every meal prepared as they like. Desserts always include sugar-free choices. The deck buffet at lunch has an extensive salad bar, and the fitness program's exercise physiologists can counsel on healthful eating on board.