Maybe you want to lose weight for your class reunion. Or perhaps you're getting married in a few months and want to look your best for the big day. Or maybe you just want to wear those skinny jeans again. Whatever your reason, it can be tempting to believe the get-fit-quick diets that promise you'll lose 20 pounds in two weeks.

But watch out. Usually, diets that seem too good to be true are too good to be true. Here's a roundup of the seven worst weight-loss plans.

1. Detox Diet:

A detox diet promises to cleanse your body of toxins and flush out fat. It's known by several different names--lemonade diet, master cleanser, maple syrup diet—and became especially popular after Beyoncé Knowles said she used the plan to lose 20 pounds for the movie Dreamgirls. Experts say the diet, which consists of drinking a combination of maple syrup, lemon juice, cayenne pepper, and water, may cause you to lose weight because of the severe calorie restrictions, but you're likely to regain the weight very quickly. It can also cause serious side effects, such as irritability, fatigue, and digestive problems.

2. Diet Pills:

Most diet pills promise extreme weight loss, either by suppressing your appetite or preventing the absorption of fat. Despite the dramatic claims, diet pills are generally ineffective and can have dangerous side effects, most commonly causing digestive problems. Weight-loss pills containing ephedra (also known as ma huang) can increase your risk for high blood pressure, stroke, and serious heart problems. In fact, in April 2004, the Food and Drug Administration pulled all supplements containing ephedra from the shelves.

3. Cabbage Soup Diet:

This plan claims that it allows dieters to lose 10 to 15 pounds a week by allowing unlimited amounts of the soup, while instructing dieters to eat only specific food combinations. For example, on the fourth day of the diet, participants should eat only the soup, as many as eight bananas, and drink skim milk. While the food limitations will cause dieters to lose weight quickly, it's an unhealthy plan, and most people have found that they've regained the weight and more after completing the diet. People who have tried the diet complain of flatulence, bloating, and feeling dizzy.

4. Calorie Shifting:

This plan sounds like it accounts for the worst part of most diets: regaining the weight. It claims that if you restrict calories on some days and eat more on other days, you'll trick your metabolism, losing weight without worries of regaining it later. Sounds good in theory, but calorie shifting sometimes requires dieters to eat a dangerously low amount of calories, leading to dizziness and lightheadedness.

5. Apple Cider Vinegar Diet:

Sometimes this diet requires drinking the vinegar; sometimes it calls for taking pills. Either way, consuming the acidic vinegar doesn't do anything to get rid of fat or speed up your metabolism, as claimed.

6. The Grapefruit Diet:

This diet promises weight loss of 10 pounds in 12 days. Like apple cider vinegar, grapefruit is declared to have fat-burning abilities, and the meal plans for this diet call for eating half a grapefruit or a glass of grapefruit juice with every meal. Most of the weight loss comes from restricting calories to about 800 a day, which is too low to be healthy. Dieters are likely to regain all weight after ending the plan.

7. Green Tea Diet:

Though green tea may improve your health due to its high antioxidant content, it's not a weight-loss miracle drug. Drinking green tea in place of high-calorie coffees and sodas could prevent your waistline from thickening over time, but simply adding green tea to your diet is unlikely to help you lose weight. Similarly, green tea extract pills or green tea patches will have minimal, if any, influence on weight loss. The good news is that green tea has no serious side effects, but you should be aware it does contain caffeine.