I have a theory that there are about 10 basic types of diets and diets within each category are very similar to each other.
I. Low-fat, low-calorie
Diets in this category emphasize limiting calories, avoid high-fat foods, and eating a healthy, balanced diet. Most diets fall within this category.
List of diets: Scarsdale diet, Rotation diet, Cabbage soup diet, Ornish diet, Pritikin diet, DASH diet, TLC diet, Mayo Clinic diet, Volumetrics, Biggest Loser Diet, Fat Belly diet, Abs diet, Daniel Plan, Joy Bauer's Life Diet, Sonoma diet, American Heart Association Diet.
My opinion: It would be healthy to be on one of these diets for a period of time, maybe 2 to 3 months. I don't believe it is possible to lose weight on these diets. Maybe some people could lose a pound per week.
II. Packaged meals
These really fit into the same category above, except for the presentation. These are the most expensive type of diets.
List of diets: Weight Watchers, Jenny Craig, Lean Cuisine, Nutrisystem
My opinion: same as above
III. Vegetarian and Vegan
These may have some health benefits.
List of diets: Vegetarians (avoid meat but eat eggs and dairy), Vegans avoid anything animal-based, including eggs and dairy. Raw food diet, Macrobiotic diet (fish)
My opinion: One would go on one of these for religious or philosophical purposes. Minor weight loss may be a side effect.
IV. Sugar Water
Maple syrup diet, Master Cleanse, Hollywood diet
My opinion: May be useful for a 48 hour fast and cleanse.
V. Diet Pills
Types: orlistat (fat blocker); sibutramine (appetite suppressant); hoodia (appetite suppressant); green tea extract (boosts metabolism); hydroxycitric acid (suppresses appetite and boosts metabolism); ephedra (boosts metabolism - banned because of dangerous side effects); chromium picolinate (appetite suppressant)
My opinion: Should be used only under doctor's orders
VI. Very-low calorie liquid diet
My opinion: May work for very obese people. Should be used only under doctor's orders
VII. Protein shake meal replacement
Slim-Fast ("a shake for breakfast, a shake for lunch, then a sensible dinner"), Cambridge Diet
VIII. High-protein, low-carb.
Banting diet, Eat Fat Grow Slim diet, Atkins diet, Paleolithic/Paleo diet, Protein power, South Beach diet, Dukan diet, Elimination diet, Eco-Atkins, Glycemic Index Diet, Makers Diet, Sugar Busters, Carbohydrate Addict's Diet
My opinion: May result in moderate weight loss if the fat content is high enough. Would be useful for maintaining weight, although a balanced low-fat diet is probably healthier.
IX. High fat diet
My opinion: This is the only way to achieve rapid weight loss, but it is unhealthy and should only be done for about three-four days before shifting to another diet.
X. Medium carb, medium fat, medium protein diets
Mediterranean Diet, Zone Diet
My opinion: These would probably be the best diets for long-term maintenance.