assuming normal low carb (avoiding white starches, etc.), it's more about will-power. Breakfast: limited fruit, omelet, plain yogurt, maybe high fiber cereal or a bit of oatmeal, lunch: salad with lean meat like fish or chicken or hamburger with lettuce, or some chinese meat wrapped in lettuce, dinner--no bread and no starch (ask for an extra salad or side of veggies). If it's too tempting, ask for then to leave off rice/potato. Taking veggies from lunch buffet and eating in room before dinner helped me avoid bread. Walk at least 30 minutes fast on the promenade deck to burn some of those carbs.