The 5:2 diet is a fad diet that emphasizes intermittent fasting. The 5:2 approach is similar to but less restrictive than alternate day fasting as adherents restrict calories for just two days per week. The diet was popularized in the summer of 2012 when the BBC broadcast a Horizon episode featuring physician, broadcaster, and author Michael Mosley explaining his experiments with fasting. A variation of the 5:2 diet is the 16:8 diet, in which the person fasts for 16 hours a day and eats meals each day in the 8 hours between 10am and 6pm.
The diet involves restricting caloric consumption to 25% of an individual's caloric needs for two days per week, and eating normally for the other five days. The diet does not actually advocate for full fasting, but rather severe calorie restriction during the two "fasting" days: the average limit for women is 500 calories, with 600 for men, although this varies based on various factors. Although the diet does not restrict any types of foods during the fast days, it is suggested that adherents focus on vegetables (especially leafy green), lean meats, eggs, soups, black coffee and tea, and water. There is no restriction placed on how often adherents may eat during the "fast days," as long as the caloric intake is kept at 25%. There is also no rule for which of the two days during the week are fasting days.
Medical opinion is that the benefits of fasting remain unproven by adequate high-quality clinical research, and adults should eat about 2000 calories a day. For some people, such as pregnant women or diabetics on medication, fasting may be unsafe.
Fasting is an ancient tradition, having been practiced by many cultures and religions. Hippocrates was known to prescribe short-term fasting to ill patients in the 4th century BC. The modern 5:2 diet was popularized in the UK in 2012 after Dr. Michael Mosley took part in a BBC2 Horizon documentary about the supposed health benefits of fasting. Interest in the 5:2 diet increased after Mosley published a series of related diet books, beginning with the first book – The 5:2 Fast Diet – in early 2013.
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