Every month, as many as 40,000 people sign up for eDiets’ free newsletter, according to Steve Johnson, the company’s CTO. And each quarter, approximately 100,000 new dieters pay $45 for a three-month subscription to the program. The subscription entitles members to weekly fitness and meal plans customized according to their eating habits, dietary preferences, medical conditions, and emotional and weight loss needs. The Deerfield Beach, Fla.-based company has more than 300,000 paying members and 9.8 million opt-in subscribers to its newsletter.

Before the company went online, Johnson worked with professional, licensed dieticians to build eDiets’ proprietary diet engine from scratch. The diet engine, which runs on Windows NT, relies on a customer database and a meal plan database connected via software. The software extracts information from each database to produce the customized diet plan for each member.

When a new customer registers on eDiets, she fills out a questionnaire, indicating her current age, weight, height and gender. Then, selecting from pull-down menus, she specifies whether she has any dietary preferences or restrictions?such as being a vegetarian?and indicates if she has any medical conditions, such as high blood pressure, hypertension, diabetes and high cholesterol. Finally, she indicates whether she’s a couch potato, exercises moderately or is very active, and if she eats when she’s stressed, depressed or upset. She submits the questionnaire to eDiets, and it gets stored in the customer database.

Not everyone gets a customized diet. The company advises dieters to check with their doctor before beginning any diet or fitness program, and they won’t give you a diet if you’re within a recommended weight range. Instead, the service may tell you that you’re within your target weight and that trying to lose additional weight is unhealthy.

For eDiets’ business to survive, it has to make sure members return to the site on a weekly basis and renew their subscriptions after three months. To encourage them to do that and ensure they feel supported in their weight loss efforts, eDiets uses the same proprietary technology the company has developed for generating the personalized diets. For instance, if the system finds that a member hasn’t logged in for several weeks, it will automatically send that individual an e-mail encouraging him to stay on track, says Johnson.

The one drawback to the plan is that many members find the online program isolating. "With an online weigh-in, there just doesn’t seem to be the motivation to stay on program the way there is with a face-to-face program like Weight Watchers," says a former eDiets subscriber.