Privacy and anonymity: "Many dieters are very self-conscious about their bodies and are sensitive to being judged. The Internet is a great way for someone who struggles with those issues, or someone who's isolated, to get some support without the scarier commitment of seeing a coach or group face-to-face," says Annie B. Kay, author of "Every Bite Is Divine" (Life Arts Press, 2007).

24/7 access: You can get to your online diet from anywhere at any time.

Time saver: "It reduces the barrier of traveling to a clinic. It also allows people to have access to a regular source of check-in even when they are traveling," says Gary D. Foster, director of the Center for Obesity Research and Education at Temple University.

Support: Internet diets offer opportunities for individuals going through similar experiences to support each other. "Hearing and seeing someone who has 'done the impossible — lost weight and kept it off' is highly motivating for many individuals. Internet weight-loss 'buddies' are helpful for many people for that reason, as well," says Janet Bond Brill, author of "Cholesterol Down" (Crown, 2006).

Cost: "They're usually much cheaper than face-to-face consultations with a nutritionist or personal trainer, and there is a ton of high-quality information available for those who know how to find it," says Kay. The typical charge is about $5 per week with a three-month commitment. Personal counseling is about $7 to $10 per week.

What are the negatives?

No accountability: "Many sites are fancy tools that offer no accountability. Individuals are often more successful at weight loss when monitored by another party (such as Weight Watchers' weekly weigh-ins). Internet diet programs often lack the interpersonal communication of one-on-one contact and support," says Brill.

Time consuming: Tracking and entering your food and activities, updating your meal plan, using the shopping lists online — it's more work then having a nutritionist assist you.

Computer skills required: You need to really know how to use the Internet and computers.

Interference: "Ads and inducements to buy products that may or may not help the dieter are everywhere, and beg the question of what type of relationship is being established," says Kay.

Lack of feeling: According to Kay, "There's no real substitute for quality personal contact. As a dietitian, when I see someone face to face, I see my client's emotions more clearly, and the nuances of a face-to-face conversation just can't be replicated over the Internet."

No activity: "Sitting at the computer is a completely sedentary activity that contributes to the couch-potato lifestyle that must be reversed to promote a lifetime of weight control," says Brill.

Maintenance is difficult: Prescriptive meal plans are difficult to stick to, even if you personalize them, and are you supposed to follow them forever?

Easy to skip: If you want to avoid dieting online — you simply don't log on. It's easier than skipping an appointment with a nutritionist. Dawn Jackson Blatner, a spokesperson for the American Dietetic Association, suggests making the online diet program your homepage.

Pricing: Many sites don't give prices until you've filled out the uninformative "diet profile."

What makes a good Internet dieting program?

According to Blatner, all online programs should include:

Blatner also warns against "scam" sites that:

Questions you need to ask yourself:

Charles Stuart Platkin is a nutrition and public-health advocate, and author of "Breaking the FAT Pattern" (Plume, 2006). Sign up for the free Diet Detective newsletter at www.dietdetective.com.