After all, diet programs that bring food to your door can run as much as $730 a month, while doing the shopping yourself means budgeting for the skyrocketing price of food. (According to the Department of Agriculture, food prices are up more than 5% since June 2007 and are expected to rise another 4.5% to 5.5% by the end of this year.)

However, sticking to a diet plan long term and adapting it to your eating habits can end up being money well spent. Just don't sign up for anything until you're sure you like it, advises Charles Platkin, founder of health web site DietDetective.com. For programs that include meals, for example, Platkin suggests dieters request samples of the food. Also, calculate all of the costs involved. For programs that don't include meals, it's important to assess what the food requirements are and calculate how much that food will cost each month. For comparison's sake, the average American consumer spent about $314 a month on food last year, according to the Department of Agriculture.

To help you better your odds of getting down to Heidi Klum size, we consulted a study by Consumer Reports, which ranks diet plans in terms of nutrition, clinical studies and long-term adherence. Below are the top five programs on Consumer Reports' list, along with commentary from our own experts and a rough breakdown of the costs involved:

1. Volumetrics

There's no monthly membership fees or prepackaged meals to pay for with Volumetrics. Dieters just need to buy a book and the rest is up to them. Developed by a nutrition professor at Penn State, this low-fat, fruit- and vegetable-heavy diet plan was deemed best overall in Consumer Reports' study. Jo Ann Hattner, a San Francisco nutrition consultant, applauds the book's recipes, in particular, which she says enable dieters to learn how to prepare their own healthy meals and alter their eating behaviors.

The costs: A one-time cost of $15.95 for the book, in addition to monthly food costs. Keep in mind that going heavy on the fruits and veggies will be expensive.

2. Weight Watchers

The industry's gold standard, which offers weekly meetings and weigh-ins, is a great fit for dieters who can't go it alone. In fact, Weight Watchers' in-person approach is the key to the program's success, says Platkin. "The idea of having to go and weigh in before a meeting gives someone an incentive to reach their goal," he says.

Weight Watchers' points system also helps educate dieters on portion control, says Hattner. "This type of program is going to generate more of a behavioral change," she says, and increase the likelihood that dieters will stick to it.

The costs: Registration is $20 and weekly meetings run between $12 and $14. Dieters can opt for a standard $39.95 Monthly Pass that includes unlimited meetings, free registration and free online tools that help them count points and track weight loss. Don't forget to add in food costs.

3. Jenny Craig

Convenience is key for dieters who choose Jenny Craig's program — number three in Consumer Reports' rankings. The program offers personal consultants and a variety of prepackaged meals. The important question, though, is how well members adapt what they've learned once they leave Jenny. "You have to be devoted to maintaining your association with the program to get you through the maintenance part, which is the hardest part of the weight loss," says Hattner. (Jenny Craig says its costs include guidance to help clients prevent weight gain once they leave the program.)

The costs: Enrollment costs range, from as little as $20 (for a three-month program) to $349 (for a year), plus the cost of prepared meals. A sample "20 pounds for $20" program lasts 90 days; members get one-on-one counseling, use of the program's online tools, and spend about $330 a month on prepared meals.

4. Slim-Fast

Even though Slim-Fast's plan consists largely of shakes and bars (to replace breakfast and lunch), Consumer Reports found that it does meet all USDA nutritional guidelines. One problem: "Anything that makes you buy their food or products is untenable in the long run because you get bored," says Caroline Apovian, director of nutrition and weight management at Boston Medical Center. In fact, Consumer Reports found that Slim-Fast had one of the highest dropout rates of the top-ranking plans.

The costs: $40 a week for shakes and bars, plus the cost of dinners and snacks.

5. eDiets.com

Web-based weight-loss program eDiets.com is highly customizable, offering members 20 diets to choose from and its own food-delivery plan. As with all online diet programs, however, dieters should be wary about being able to stick with a totally self-managed program, says Platkin.

The costs: Online plan is $18 a month, plus the cost of food. The meal plan costs $140 a week plus $20 in shipping costs. Total: $160 a week or $638/month.