Choose an online diary that offers accurate nutrition information, flexibility and ease of data entry. Test the site by entering your food intake for a particular day, and then cross-check the nutrition analysis -- calories, fat, sugar and other nutrients -- against a nutrition text from the library. Ensure that the database includes the foods that you normally eat and also allows you to add food items if needed. Preview any additional features, including nutrition analysis, reports, exercise tracking, fitness advice and user forums to see whether they meet your needs.