The phrases food faddism and fad diet originally referred to idiosyncratic diets and eating patterns that promote short-term weight loss, usually with no concern for long-term weight maintenance, and enjoy temporary popularity.
Scientific view 
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"Fad diet" is a term of popular media, not science. Some so-called fad diets may make pseudo-scientific claims, but others labeled "fad" are based on science[dubious ]. According to one definition, fad diets claim to be scientific but do not follow the scientific method in establishing their validity. Among the scientific shortcomings of the claims made in support of fad diets:
- not being open to revisions, whereas real science is
- observations that prompt explanations are used as evidence of the validity of the explanation
The term "fad diet" has been pulled into the debate in the scientific community over the physiology of weight gain and loss. It has been used by proponents of established views to refute claims of non-traditional methods of weight loss such as low-carbohydrate diets. Some researchers hold to the established belief that weight loss is strictly a function of a reduction in caloric intake, and that no other strategy can help dieters achieve long term weight loss.
Fad diets 
Food fad is a term originally used to describe simple, catchy diets that often focused on a single element such as cabbage, grapefruit or cottage cheese. In 1974, the term was defined as three categories of food fads.
- A particular food or food group is exaggerated and purported to cure specific diseases.
- Foods are eliminated from an individual’s diet because they are viewed as harmful.
- An emphasis is placed on eating certain foods to express a particular lifestyle.
Food fad is also used by media and the scientific community to refer to diets that do not follow common nutritional guidelines, regardless of their actual status as a fad; for example, the Atkins and Paleo diets are commonly referred to as food fads, even though they have enjoyed cycles of popularity for several decades. Thus, while called food fads, they are not actual fads (which are defined by sharp but brief spikes in popularity).
FamilyDoctor.org, a publication of the American Academy of Family Physicians, for example proclaims that fad diets "typically don't result in long-term weight loss and they are usually not very healthy. In fact, some of these diets can actually be dangerous to your health. They then offer a long list that includes low-carbohydrate diets in general and Atkins, the Zone diet and three others by name. One scientific study contradicts the website's assertions. A 2007 study published in the Journal of American Medicine concluded that overweight premenopausal women age 25 - 50 without any heart, renal, kidney, or diabetic disease on the Atkins diet lost more weight than those on specific low-fat diets after 12 months. The researchers concluded that low-carbohydrate diets are a "feasible alternative recommendation for weight loss." However, this study did not compare the Atkins diet to calorie restriction diets.
Programs often considered fad diets:
- Cabbage soup diet
- Grapefruit diet (a.k.a. the Hollywood Diet and erroneously as the Mayo Clinic Diet)
- Israeli Army diet
- Nutrisystem
- Paleolithic diet 
- South Beach Diet
- Gerson therapy
- Low-fat diet
- Morning banana diet
- Low-carbohydrate diet 
- High carb/low fat diets
- Controlled portion sizes
- Food combining
- Liquid diets
- Diet pills and herbal remedies
- Eat Right For Your Type: The Blood Type Diet
- Baby Food Diet
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- "Nutrition for Weight Loss: What You Need to Know About Fad Diets". Familydoctor.org. Retrieved October 13, 2012.
- Scott, Jennifer R. (2008-11-10). "What You Need to Know About The Mayo Clinic Diet". About.com: Weight Loss. About.com. Retrieved 2009-03-25.
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- "Nutrition for Weight Loss: What You Need to Know About Fad Diets". familydoctor.org. 2004-02-01. Retrieved 2011-09-19.