When it comes to the most effective weight-loss programs, there's no better way to sort fact from fiction than with a long-term medical study. They make for dense reading, but research studies are ideal sources of unbiased information on diet plans. Most popular diets haven't been subjected to long-term clinical studies, but we found solid research about Weight Watchers, the Atkins Diet, the Zone Diet, Slim-Fast, Dean Ornish's "Eat More, Weigh Less," Rosemary Conley's "Eat Yourself Slim," Jenny Craig, the Mediterranean diet and "The Volumetrics Weight-Control Plan" published in peer-reviewed medical and science journals.
Among reviews in the mainstream press, Health magazine offers the best analysis of diet plans, evaluating dozens of popular weight-loss programs and using an expert panel to pick 10 of the healthiest options available. U.S. News & World Report also employs an authoritative team to analyze 26 commercial diets, ranking them in categories including safety, nutrition, and long- and short-term weight loss. Another useful resource is WebMD.com, where editors track down expert opinions on nearly every popular weight-loss plan. ConsumerReports.org published a 2011 analysis of seven diet plans and books, but gives only brief information about each.
User reviews from sites such as Viewpoints.com, Epinions.com and DietsInReview.com are very helpful for gauging the opinions of regular dieters. This kind of information is often absent in professional reviews, such as how easy the diet is to stick to or whether the program provides the motivation and support it claims to offer. Most diet books also have 100 or more Amazon.com user reviews that provide the same sort of feedback.
A couple of tenets are true for any weight-loss plan. First, exercise is key. Although research indicates that physical activity alone might not be much help -- you can easily eat enough calories to compensate for what you burn -- the American Council on Exercise says "the combination of exercise and diet is more effective than diet alone." Working out is also essential to keeping the weight off.
Second, dieters who get long-term support, either in person or online, are more likely to maintain their weight loss than those who don't. We found studies suggesting that online and telephone support may offer the same benefits as in-person support for maintaining weight loss, but this hasn't yet been proven. Although websites like eDiets.com provide virtual support to dieters (which many find useful), Weight Watchers is king when it comes to face-to-face meetings.
In terms of efficacy, most scientific studies show that the majority of popular diets will lead to short-term weight loss as long as you stick with them. For example, a University of Surrey study published in the journal Public Health Nutrition observed 300 overweight or obese subjects as they followed several mainstream weight-loss plans, including the Atkins Diet, Weight Watchers and Slim-Fast. Over the course of six months, all the participants lost a similar amount of weight (between 11 and 19 pounds) regardless of the diet they followed.
When it comes to the low-carb vs. low-fat debate, experts say either diet can help you shed pounds. In a 2010 study published in the Annals of Internal Medicine, researchers at Temple University divided more than 300 people into either a low-carb or a low-fat group. The low-carb diet limited carbohydrates to less than 20 grams per day for three months, then gradually added more carbs. The low-fat diet plan contained less than 30 percent of subjects' total daily calories from fat. At the end of two years, both groups lost roughly the same amount of weight (15 pounds on average). "Successful weight loss can be achieved with either a low-fat or low-carbohydrate diet," the researchers conclude.
However, dietitians and other experts often express concern about the severely restrictive nature of super-low-carb diets. Not only are these plans extremely challenging to follow, but they also pose a risk of nutritional deficiency by completely, or almost completely, eliminating food groups. Scientists are still unraveling just how a nutritionally complete diet aids weight loss; for example, in a Journal of Nutrition study published in July 2011, researchers found that a high-protein, high-dairy diet encouraged reductions in visceral fat volume, body fat percentage and trunk fat mass.
Nonetheless, the entire, still-evolving body of research confirms that weight loss is a simple formula of calories in vs. calories out, so any diet that reduces calories will help you shed pounds. The trick is choosing a diet that provides balanced nutrition, then following it until you get to your goal weight. All of the medical studies we found concluded with the same advice: The best diet is one that you can stick to.
In addition, studies show that those who self-monitor -- that is, tracking the foods you eat and the exercise you do -- are ultimately successful at losing weight. This personal accountability can help you shed pounds whether you follow a commercial diet program or design your own. Websites and mobile apps such as CalorieCount.com and NutriData.com make food-journaling easy, as do many of the tools on the best-reviewed diet websites, including eDiets.com (*Est. $19 per month) and SparkPeople.com (free). For more on how to keep a weight-loss journal, see our blog article, "Reach your resolutions for free." (Note: ConsumerSearch is owned by About.com, which also owns CalorieCount.com, but the two don't share an editorial affiliation.)