The popularity of the Atkins Diet and other low-carbohydrate weight management solutions has skyrocketed in the last year or two—but what health concerns do they present?

Susan Learner Barr, M.S., R.D., the director of program development for Weight Watchers North America, who is a registered dietician and has a masters degree in science and human nutrition, says the low-carb way of life can be dangerous.

"I think that Atkins and other low-carb plans are highly restrictive. For instance, the plan allows little to no fruits, vegetables, pastas and other whole grains—and as a nutritionist, I can tell you this is an unhealthy way to eat," she says. "These restrictions really have their downside—you're not getting the vitamins and fiber you need. Because of this, you can get constipated, and you need a lot of supplements to make up for what you're not getting from those foods."

Barr adds that there can be some undesirable side effects in addition to these health concerns.

"There can be other side effects such as bad breath and even depression," she warns.

Barr says that low-carb plans such as Atkins rarely culminate in long-term or permanent weight loss.

"The minute one tries to eat healthfully again, and go off the diet and add things like carbs back in, he or she gains weight back, because most of what is lost is water weight. It's difficult to maintain," she says.

Weight Watchers and Jenny Craig are two of the oldest and most popular mainstream weight loss systems around. Representatives from both companies say they have made only a few changes in light of the low-carb craze. The biggest thing both companies say they have done is to make programs more personalized to each individual client.

Weight Watchers' Alternative

At the end of August, Weight Watchers introduced its new Turnaround Program.

In the company's research to create this program, Barr says Weight Watchers came to one important conclusion.

"People responded to a simple approach that does not require counting or tracking for the most part—they found that very appealing," she said.

The Turnaround Program is made up of two systems. One is Flex Points, Weight Watcher's longtime staple for which it is perhaps best known. Flex Points is based on a points system—everything eaten is assigned a point value according to calorie, fat and fiber content. Clients are allowed a certain number of points per day, based on their current weight.

The second system is the new Core Plan. This plan involves no counting or tracking, for the most part. Each day, clients eat from a core list of foods from every food group, including carbohydrates. Barr says all the foods are high in nutritional quality and low-energy density, which she says research has shown to be more filling and satisfying, because it is higher in water and/or fiber content.

Jenny Craig's Alternative

Lisa Talamini, a registered dietician and the director of program development for Jenny Craig Inc., also finds the low-carb approach to be unhealthy and a poor solution to weight loss.

"So much of the low-carb approach is about taking things away, being deprived of things you want to eat," she says. "People eventually stop losing weight over time because they get bored and fall off."

Talamini says Jenny Craig's approach is rooted in science and credible information. Earlier this year, she says the Institute of Medicine came out with new guidelines for carbohydrates, proteins and fats. Previously, Jenny Craig's menus were based on 55 to 60 percent carbohydrates, 20 to 25 percent protein, and 20 to 25 percent fat. Jenny Craig adjusted its program recently to reflect the institute's new guidelines; now, programs can be as low as 45 percent carbohydrates, and Jenny Craig has introduced some new lower-carb, higher-protein foods and products.

"Clients can make personal choices—if they want a plan that is more low-carb or higher protein, they can have that," says San Jose Market Director Tiffany Lawrence O'Leary.

Kindu Kaur, center director of Jenny Craig's Almaden Center, says she thinks that since Jenny Craig's program shows results, clients are happy with it the way it is, and don't typically request fewer carbs than the program offers.

For more information on Jenny Craig, call 800. Jenny.Care or visit www.jennycraig.com. For more information on Weight Watchers, visit www.weightwatchers.com. For more information on Atkins, visit atkins.com.