A system and method for method defining, creating, and managing meals according to user preferences regarding a diet plan, preferred foods, preferred meal preparation options, and meal times. An expert system uses information about an individual's diet preferences and related goals, to develop a personalized plan including a complete meal plan and to generate meal suggestion messages for each meal. Meal suggestion messages are transmitted to users' portable devices at their preferred meal times. If a user accepts a meal suggestion, nutritional information regarding the accepted meal is tracked and considered in determining the user's progress toward a goal. If a user rejects a meal suggestion, the expert system generates a meal substitute suggestion or a specific food item substitute suggestion. When the user accepts the substitute suggestion, nutritional information regarding the substituted meal or food item is tracked and considered in determining the user's progress toward a goal.