If Marie Osmond, Queen Latifah and Valerie Bertinelli can follow a diet plan and lose weight, you ought to be able to too, right? That's why millions of people every year turn to three of the nation's top weight-loss programs.

But how do they differ, and which one might be right for you?

Weight Watchers is famous for its POINTS system, which can be found on food labels and restaurant menus across the country.

"Every food has a POINTS value, which is calculated based on a food’s calories, fat and fiber," according to the company's Web site. "POINTS values help you keep track of what you eat, so that you stay within a daily POINTS target that’s personalized for you, based on your height, weight and other factors."

Weight Watchers combines that with online or in-person meetings to help you retool your lifestyle and food choices. Meetings cost $10 to $12 per week, depending on location, and the first month of the online program is about $46.

Jenny Craig offers a whole line of food that helps users learn eat correct portions. It offers in-person counseling sessions that include taking body measurements, setting goals and talking about exercise.

The cost of Jenny Craig depends on which plan and which menu items are selected.

NutriSystem sells nutritionally balanced meals based on the glycemic index, which is a theory that suggests good-quality carbohydrates, which are digested more slowly than simple carbs, help eaters feel full longer without dramatic swings in blood sugar.

The women's program cost $299 for a 28-day food supply and the men's is $329 for 28 days of food.

Which One's For You?

Miranda Thiel, 20, researched all the programs on the Internet before she settled on Jenny Craig. The college sophomore said she needed someone to hold her accountable.

"I was eating, at the start (of the program), 1,700 calories (a day) and before that, God only knows how many calories I ate," Thiel said. "I thought that was going to help me, to go in every week and weigh on someone's scale."

Thiel also tried Weight Watchers, but without much time to cook, she said she preferred Jenny Craig's approach. Plus, she didn't like counting POINTS .

Working with her Jenny Craig counselor, Thiel lost 40 pounds and went from a size 16 to a size 9 over 11 months. She said her biggest challenge has been applying what she learned by eating Jenny's food to decisions in the grocery aisle.

What To Expect

Thiel's weight-loss journey on Jenny is just what dietitians expect.

"(Jenny Craig and NutriSystem) can be helpful for people who want meals done for them and don't want to think about it," said Hy-Vee supermarket registered dietitian Carrie Nielsen. "They're ready to lose weight, but they don't want to put in the cooking work. You get three meals and a snack a day. It's good for a person who's busy."

Nielsen said the prepackaged programs can be a good way to get a weight-loss program back on track quickly.

"A lot of these meal plans are 1,200 to 1,500 calories -- if you consume only that you will lose weight if you eat only what they send you," she said.

On the downside, Nielsen said, going back to cooking from either Jenny Craig's or NutriSystem's packaged meals can be a tough transition.

"I know someone who lost 100 pounds on (NutriSystem) and she's reluctant to go off of it because, what does she do now?" Nielsen said. NutriSystem's Delthine Carroll said that transition is part of what the company's counselors are there for -- helping people make better decisions.

One complaint dietitians have about Jenny and NutriSystem is that local counselors are usually not trained dietitians, though registered dietitians are available on the corporate level.

What Do Experts Say?

Some dietitians also dislike the preservatives in prepackaged food and the expense they can run up.

"The price of these things -- in my mind, if you're going to rely on processed foods, you've got Healthy Choice in the supermarket, so why are you buying into their stuff?" said Creighton University Medical Center registered dietitian Joni Pagenkemper.

Florida-based health coach Sharyn Lustre said she steers clients away from all of the national diet programs in favor of teaching them to think about exactly what they're eating and rely on the bottom-line equation: Eat less than you burn and you'll lose weight. But even Lustre, along with Pagenkemper and Nielsen, said Weight Watchers comes as close to true behavior modification in a livable, long-term program as any in the group.

"Weight Watchers is one I do recommend and support because it's more cost effective, they're everywhere, they have more longevity in terms of their outcomes, and it's been supported by (the Journal of the American Medical Association)," Pagenkemper said. "Weight Watchers is not a diet. The others are focused on dropping weight quick. Weight Watchers is changing your habits."

"It actually educates you about the food groups and good, healthy eating choices," Lustre said. "They're very adamant about a healthy weight for your height before you set goals. They will not let you go below what's healthy for you."

On the downside, dietitians said the responsibility and accountability required for Weight Watchers to work will turn some people off. Users have to cook for themselves, figure out portion sizes and keep strict track of POINTS. Many people may want to lose weight but don't want to go to group meetings or weigh publicly, though the online version offers an alternative.

Got A Better Idea?

The experts said there are even better ways to not just drop pounds, but truly change your relationship with food. Pagenkemper said even a single session with a clinical dietitian could pay for itself in spades.

"We're like, the price of a haircut or two. This is your life and health we're talking about," she said.

Those who can't afford even one appointment can start with the registered dietitians at many grocery stores. They are people like Nielsen who give store tours and help customers understand labels.

One of the top tips Nielsen doles out for free: Start a food journal and write down everything that passes your lips.

And get some support. One of the best aspects of Weight Watchers, NutriSystem and Jenny Craig, the experts said, it their access to online, in person and over-the-phone counselors who cheer you through the process.

You can create that yourself, they said, by recruiting a spouse, colleague or sibling to take the journey with you.