1. 3 Hour Diet

- The 3-Hour Diet involves eating small portions every three hours throughout the day. The theory is that eating constantly will keep your metabolism continually running at a high rate and burning fat. There are no prohibited types of food—only portion restrictions. Fried chicken, candy bars, bacon, and red meat are allowed.

2. Atkins Diet

- The Atkins Diet emphasizes eating lean protein and low-starch vegetables and avoiding simple carbohydrates such as flour and sugar. The diet involves a reduced glycemic load (carb content) to keep blood sugar levels in a healthy range. In theory, consuming fewer carbohydrates allows your body to burn greater amounts of fat. 

3. Best Life Diet

- The Best Life Diet attempts to change the way you eat, exercise, and live to achieve better health. Its goal is to tackle the root cause of overeating. The diet was designed to counter the quick-fix mentality of most diet programs out there. The Best Life Diet promises to help you discover why you were out of shape to begin with and inspire physical and emotional changes that will last a lifetime.

4. Blood Type Diet

- The Eat Right for Your Type diet (Blood Type Diet) advises people to eat certain foods based on their blood type: A, B, AB, or O. The plan posits that each blood type digests food proteins (called lectins) differently and that eating the wrong food proteins can cause ill effects on the body—including slower metabolism, bloating, and even certain diseases. According to this diet, avoiding bad food proteins will help you achieve better health.

5. Cabbage Soup Diet

- As its name suggests, the Cabbage Soup Diet involves eating a very limited diet primarily made up of cabbage soup for a week in order to achieve quick weight loss. The diet promises rapid weight loss—about 10 pounds in a week and is promoted as a "vanity diet"—a quick way to lose a few extra pounds to look good for a special occasion.

6. Caveman Diet

- The Caveman Diet focuses on eating foods from the Paleolithic era of human nutritional needs—foods we ate prior to farming and domesticating animals. The goal is to train your body to crave healthy foods. This diet promises to achieve your ideal body weight, sharpen the mind, and enhance a connection to your body’s inner being—similar to a wild animal's keen hunting instincts.

7. Fat Flush Diet

- The Fat Flush Plan folds weight loss into a low-carbohydrate, restricted-calorie diet. The notion is that the liver is a "fat-burning furnace," and the right combination of foods and a specific eating schedule will increase metabolism and cause the body to burn fat efficiently. The diet promises to cleanse the liver, which, in theory, will help melt fat and cellulite away from the waist, hips, and thighs.

8. French Women Don't Get Fat Diet

- The French Women Don’t Get Fat Diet is based on the creator’s theory that French women don’t diet, count calories, or skip meals. Instead, French women develop a balanced relationship with food and remain thin. The diet involves eating high-quality foods in moderate portions. Instead of counting calories or cutting out certain foods, this diet promises that you’ll be able to trim down without giving up the decadent things in life.

9. Glycemic Index Diet

- The glycemic index (GI) is a scientific ranking that classifies foods based on how quickly they raise blood sugar levels. High-GI foods trigger a rise in blood sugar and release insulin, which is thought to trigger fat storage, intensify hunger, and lead to weight gain. The premise is that by avoiding foods that have a high-GI score, your appetite will decrease, and you will subsequently lose weight.

10. Grapefruit Diet

- The Grapefruit Diet is a meal plan with a primary focus on consuming grapefruit or grapefruit juice at every meal. Foods can be prepared with spices, dressings, or butter. Some caveats include no extremely hot or cold foods, nothing prepared in aluminum pans, and keeping “protein meals” and “starch meals” at least four hours apart. Used for more than 80 years, the diet’s goal is quick weight loss with a daily caloric intake less than 1,000 calories.

11. The Hormone Diet 

- The Hormone Diet suggests that hormone fluctuations can negatively affect a person’s weight, as well as other factors that can contribute to weight gain. The diet is designed to sync hormones with diet, exercise, nutritional supplements, and detoxification. The diet regulates what you eat and indicates the right time to eat to ensure the maximum benefit to your hormones.

12. Jenny Craig

- Jenny Craig is a three-tiered personalized weight loss program that focuses on food, body, and mind. The core of the diet is portion control that begins with prepackaged meals, which are usually frozen. The program also provides support to dieters through one-on-one consultations. The ultimate goal is to wean people off the prepared meals and teach them to make healthy food choices on their own.

13. Macrobiotic Diet

- A blend of Buddhism and Western practices, this diet is more of a life makeover—macrobiotic means “long life”—to achieve both physical and Zen-like mental harmony. The diet is primarily vegetarian, with some fish and seafood, and focuses on natural and organic foods. True followers of the diet opt for fresh, locally grown foods. The diet's nod to Eastern philosophies supports the idea of achieving a yin-yang balance from food.

14. Master Cleanse Diet

- The Master Cleanse Diet is a liquid diet used to detoxify the body and encourage weight loss. The diet is meant to be strictly followed during a three- to 10-day period. It is broken up into three phases: Ease-In, The Lemonade Diet, and Ease Out. The Master Cleanse Diet claims to make the body healthier and energized while removing toxins from the body and promoting weight loss.

15. Mediterranean Diet

- The Mediterranean Diet encourages an all-encompassing healthy lifestyle through consumption of simple, fresh foods and fitness. Based on the traditional eating habits of poor coastal regions of Southern Italy, Crete, and Greece, it includes vegetables and legumes, fresh fruit, olive oil, and moderate amounts of fish, poultry, and red wine. The diet promises healthy weight loss, along with numerous other health benefits.

16. New Beverly Hills Diet

- The New Beverly Hills Diet is an updated version of the original that was published in 1981. The diet suggests that food doesn't inherently cause weight gain; inefficiently digested food is to blame. The diet encourages eating the right foods at the right time and paying particular attention to food pairing—that is, which foods you are eating together.

17. Nutrisystem Diet

- The Nutrisystem Diet is a prepaid meal plan with 28 days worth of meals (breakfast, lunch, dinner, and dessert) delivered to your door. Menus provide a mix of low-glycemic carbohydrates, plenty of fiber, and lean protein. Daily caloric allowances are restricted to 1,200 for women and 1,500 for men. Nutrisystem offers support from registered dietitians throughout the program.

18. Shangri La Diet

- The Shangri-La Diet has one rule: Take 1 to 3 tablespoons of extra light olive oil and/or 1 to 2 tablespoons of sugar water twice daily between meals. The premise is that the body learns to associate flavorful foods with calories, thus leading to overindulgence and weight gain. In theory, by consuming olive oil and sugar water, which have calories but little taste, you teach your body to stop associating flavor with calories, and it will want less food.

19. Skinny Diet

- The Skinny Diet claims to be “a no-nonsense, tough-love guide for savvy girls who want to stop eating crap and start looking fabulous." The diet requires a full transformation to a vegan diet—banning sugar, meat, dairy, alcohol, and caffeine—and promoting fruits, vegetables, soy, nuts, legumes, and green tea. The premise is that being skinny means being healthy. It’s about eating what’s good for you and passing on what’s not. 

20. South Beach Diet

- The South Beach Diet was designed by a Florida doctor and dietician to help people lower their risk of developing heart disease. The goal is to replace "bad carbs" with "good carbs" and "bad fats" with "good fats." So nix refined sugars and processed grains in favor of vegetables, beans, and whole grains and replace saturated fats with foods rich in good fats and omega-3 fatty acids, such as salmon and avocado.

21. Volumetrics Diet

- The Volumetrics Diet aims to empower readers to quit on-and-off dieting for good by living a healthy lifestyle based on nutritious food and regular exercise. The diet focuses on the “energy density” of foods (the number of calories in a specific amount of food). This low-calorie, high-volume eating plan includes foods with a lot of water and fiber, as both can increase your sense of fullness.

22. Weight Watchers Diet

- The primary focus of Weight Watchers is long-term weight management with a commitment to better eating habits and a healthier lifestyle. There are no forbidden foods. Instead, a point system ascribes values to foods. To achieve weight-loss goals, dieters must stay under a certain number of points for foods consumed. Support and education are part of the comprehensive approach to healthier food and exercise choices.

23. The Zone Diet

- The Zone suggests that food can affect the hormonal response of the body and cause changes in insulin production. The diet suggests a food plan with a balanced ratio of carbohydrates (40%), protein (30%), and fat (30%). This mix is optimal for how the human body is genetically programmed and will allow the body to enter an efficient metabolic state ("The Zone").