NEW YORK (CNN/Money) - You promised yourself that you'd take off 15 pounds by Memorial Day but halfway through the summer you're still struggling to get rid of that extra weight.

Ready to call Jenny?

Weight Watchers International, Jenny Craig, and L.A. Weight Loss -- the three largest commercial weight loss franchises -- have received praise from industry experts for their fitness-based approach to weight management. But if you're thinking about joining one of these programs, you'll pay a premium for each pound that you lose.

Jenny Craig encourages its participants to buy their proprietary line of foods, which boosts the price you'll pay for each pound of weight loss. Food is purchased on a weekly basis, and depending on the menu you choose, costs between $10 and $15 a day.

The program fees also vary based on the type of weight loss program you select. Jenny Craig's platinum program is a lifetime membership that offers unlimited weight loss and follow-up maintenance for $399. The gold program offers a year of unlimited weight loss and maintenance for $199.

Both Weight Watchers and L.A. Weight Loss offer less expensive dieting options. The initiation fee for Weight Watchers ranges from $15 to $30, depending on the region where you join and the average weekly cost for dues is $12. L.A. Weight Loss offers customized diet plans that start at $7 a week, not including the program's initiation fee, which is approximately $129 in the New York City area.

But it's your target weight that usually dictates how much these programs will cost you per pound of weight loss.

Experts warn that losing more than two pounds a week can be hazardous to your health. Dr. Sunita Jayakumar, M.D., however, thinks that a pound a week is a safer but more conservative approach to healthy weight loss.

So how will that affect your checkbook?

Assuming you consistently lose one pound a week for 15 weeks, you can expect to pay $83 for each pound you lose on Jenny Craig's gold plan, assuming you spend $70 a week for food, or $13 on Weight Watchers, including a $15 initiation fee.

Constructing your own fitness plan is certainly a cheaper weight loss option, but there is some evidence that it may not be as effective as commercial dieting centers.

"For many people, [Weight Watchers] would be a good program to try, especially if they feel the group setting will be helpful to them and keep them motivated," said Dr. Stanley Heshka, Ph.D.

The problem with solo dieting, he adds, is that "you start out with all of these good intentions but 2 or 3 weeks later other things pop up and 5 months later you've forgotten about it."

Healthy living Web sites • The American Heart Association • American Council on Exercise (ACE) • President's Council on Physical Fitness

Weight Watchers commissioned the New York Obesity Research Center to conduct a long-term study of its program that began in 1998. Researchers, led by Dr. Heshka, randomly assigned participants to either a self-directed weight loss program or to a Weight Watchers program and tracked their progress over a two-year period.

The final report, published in the Journal of the American Medical Association (JAMA), noted that the Weight Watchers participants lost an average of six pounds over the course of the study, compared to less than a pound of weight loss for those who followed a self-directed program.

Dr. Jayakumar believes that commercial weight loss programs such as Weight Watchers can provide sound guidance to moderately overweight individuals looking to lose 20 to 30 pounds but she refers dieters who have medical problems to health professionals.

"Patients with multiple medical problems need to be advised by a medical professional as well as a registered dietician," she said. "They can't just go to a weight loss center, because they need medical attention."

Don't be lulled into thinking that such programs will make dieting any easier, especially if weight loss has become a regular New Year's resolution.

Weight loss, Dr. Jayakumar explains, can be a "frustrating ordeal" because it often takes several months for dieters to reach their fitness goals.

She also warns that advertisements featuring former clients who've lost several pounds in a relatively short period of time are misleading.

"It creates an illusion that they are the ones who are going to make you lose the weight. In reality, it's up to you to lose the weight," she said before reiterating that safe weight loss should be limited to a pound per week.

Commercial weight loss centers sell a service which may or may not work for you. So keep in mind that the sales representative telling you about the program is there to hook you on their product, not guide you towards your fitness goals.

And like anything else, there are no guarantees that you will achieve your ideal weight on any of these programs, let alone be one those success stories featured on the program's advertisements.