There's no getting around it -- a whopping 55 percent of American adults are overweight, according to the U.S. Department of Agriculture. That hefty statistic leaves many of us searching more frantically than ever for the magic weight-loss answer. All those glossy hardbacks on display at the bookstore provide the diet fodder we're hungry for: Dr. Atkins' New Diet Revolution, The Zone, Sugar-Busters! ...

While these diet programs promise quick and effortless weight loss, many experts think that the only guaranteed weight loss will be from your wallet. So why are these "fad diets" so wildly popular, and do any of them actually work?

The lure of fad diets stems from the fact that most of them offer a quick fix. "Fad diets really give a great promise ... and a lot of them really do give quick results," says Leslie Bonci, director of sports nutrition for the Department of Orthopedic Surgery at the University of Pittsburgh.

There's no strict definition of a "fad diet," according to experts, but a common thread is the tendency to categorize foods in the extreme: Certain foods are either good or bad, entire food groups are restricted or eliminated, and changes in eating behaviors are not promoted.

According to Bonci, "Fad diets pretty much all promise that you only have to do them for a short amount of time. They usually rely on some kind of a gimmick -- for example, an emphasis on protein to the exclusion of all else, or some kind of food combination, or a particular mix of things," that will draw your attention purely because it's unusual.

Bonci explains that the majority of popular diets fall into four basic categories:

Despite the controversy that surrounds these diets, each diet has its share of staunch supporters. Take the Atkins diet, for example, which is currently enjoying a surge in popularity since the 1992 re-publication of founder Dr. Robert Atkins's first book from the 1970s. Atkins's high-protein, low-carbohydrate eating plan was also recently co-opted in Barry Sears's wildly popular book The Zone, published in 1995.

The Atkins diet promises that "your overall health will improve, you'll feel better, and you won't feel hungry between meals." Judith Mattart, 60, from Yuma, Arizona, swears by the Atkins way of eating. "I cannot say I have lost any weight on the Atkins diet; however, I enjoy some benefits I never expected. The main thing is I never slip, I don't cheat, and I'm never hungry."

Other veterans of the Atkins diet, however, have experienced some negative side effects. Catherine Bishop, 26, from Atlanta, Georgia, says that "it was so completely different from how I normally eat ... the total reversal in my eating pattern really knocked me over. I felt fatigued and groggy."

The importance of consulting your physician

The consensus is that not every diet is right for every person. If you're wondering whether to try a particular diet, how do you decide if that diet is right for you? Ann Grandjean, executive director of the Center for Human Nutrition, in Omaha, Nebraska, says that "when it comes to dieting, there is no one program that will meet the needs of all people." Grandjean adds that "we need to prescribe the diet for the individual who's trying it. For example, someone who has extremely high cholesterol levels and very low triglycerides may do well on a low-fat, high-carbohydrate diet ... but it is best to get the advice of your physician."

Denise E. Bruner, M.D., president of the American Society of Bariatric Physicians (specializing in the treatment of obesity and its related conditions), agrees that "there's no one specific diet that is appropriate for everybody, and we're all different. I think a program has to be tailored to the individual needs of a patient."

Diets to avoid

Experts do say there are several diets you should not attempt. "The scariest diets we see are extremely restricting in calories, with limited nutrient intake and no attempt to take supplements," says Grandjean. "Any time the calories are low and the number of food groups is limited, then the bigger the scare." Dr. Bruner recommends steering clear of diets that do not provide a wide variety of nutrients and that promise immediate, unrealistic weight loss.

With all these choices, then, what is the best way to lose weight? "I look at food ingestion like a caloric budget," says Dr. Bruner. "If you are taking in more than the budget calls for, then there's going to be an excess there. It is about calories. If you look at Atkins, Sugar-Busters!, or The Zone, most of the food plans are a 1200- to 1500-calorie plan, so this will create a caloric deficit, and you will lose weight."

Exercise is key

The experts concur that exercise is a necessary part of any diet plan. "Everyone on a weight-loss plan will eventually plateau, and exercise is then the best way to jumpstart a weight-loss program," says Grandjean. Dr. Bruner agrees, explaining that "we can never lose sight of the importance of physical activity. It is not only diet that makes a difference; it is also engaging in physical activity on a continual basis."

"We use the word diet and we think it means a temporary fix. What we need to do is make changes in our lifestyle. Unfortunately, this is not as palatable as a quick fix," says Grandjean.

So, there's no free lunch here. If you want to lose weight, you'd better make sure that lunch is nutritionally balanced, low in calories, and good for you too.