The Worst Diets Ever: Diets That Don't Work

"Eat what you want, when you want, and watch the pounds disappear!" You've heard of them, maybe even tried them: miraculous-sounding diets that claim to melt off pounds with minimal effort. There are hundreds of these quick-fix diets out there, from the grapefruit diet to the detox diet to the "caveman" diet. But how do you tell legitimate weight loss plans from diets that don't work (at least in the long run)?

One reason's it's so hard to tell the difference is that even the worst diets will likely result in weight loss, at least initially. But it does little good to lose weight, experts say, if it comes right back.

"Don't be fooled into thinking it is because of some magical food, pill or potion. What causes weight loss is eating fewer calories than you burn," says Dawn Jackson-Blatner, RD, a spokesperson for the American Dietetic Association (ADA).  "Crazy, unbalanced diets cause weight loss because they are basically low-calorie diets."

After a few weeks on an unrealistic diet, dieters usually become frustrated and give up. This leads to feelings of failure that can help send them right back to their unhealthy lifestyles.

"Fad diets not only fail to produce long-term weight loss, they can lead to deprivation, weight gain, and discouragement," says Michelle May, MD, author of Am I Hungry?What to Do When Diets Don't Work."In other words, you are often worse off than before you started."

The Worst Diets Ever

Experts who spoke to WebMD identified these 5 types of diets that are unlikely to produce long-term results for most people: 

1. Diets that focus on only a few foods or food groups (like the cabbage soup diet, grapefruit diet, strict vegan diets, raw food diets, and many low-carb diets). Beware of any diet that rules out entire food groups. People need to eat from a variety of food groups to get all the nutrients they need, says ADA spokeswoman Andrea Giancoli, MPH, RD.

Yale University's David Katz, MD, author of The Flavor Point Diet, says that while restrictive diets do work initially, they fail over the long haul. You can lose weight on diets that focus on single foods (like cabbage soup), but how much cabbage soup can a person eat?  Before long, you grow weary of eating the same foods every day, and cravings for favorite foods lead you back to your former eating behavior.

Keep in mind that all foods can fit into a healthy lifestyle in moderation -- even things like bacon, super-premium ice cream, and chips. And when diets forbid certain foods and dieters envision a life without their favorite treats, those diets usually fail.  "Any time you restrict a certain food, it triggers cravings for the forbidden fruit and sets up a restriction-binge cycle," says Blatner.