5:2 Diet (5:2 Intermittent Fasting)

The 5:2 diet is a form of intermittent fasting in which you eat normally five days a week and sharply reduce calories (approximately 500–600 kcal) on two non-consecutive days. It does not necessarily change what you eat; it reduces total intake across the week.

The advantage is that severe restriction falls on only two days, leaving the rest of the week free. On the downside, fast days can be hard to endure, and some people compensate by eating more on normal days, which cancels the deficit.

History and origin

The 5:2 diet was popularised by British journalist and physician Michael Mosley in 2012, after he made the BBC documentary Eat, Fast and Live Longer, in which he personally investigated the effects of caloric restriction and intermittent fasting. The documentary generated considerable public interest in the UK and paved the way for a book. The Fast Diet, published in 2013 alongside writer Mimi Spencer, sold millions of copies worldwide and officially launched the term “5:2” into the popular vocabulary of dieting.

The scientific foundation of the approach comes from the research of Mark Mattson at the National Institute on Aging (NIA/NIH), who studied for decades the effects of intermittent caloric restriction on metabolism, brain function and longevity in animals and humans. Mattson published numerous studies suggesting that periods of fasting trigger beneficial cellular adaptations, including autophagy and regulation of insulin sensitivity — arguments that Mosley picked up and popularised.

After 2013, the 5:2 diet attracted the attention of clinical researchers, with several studies comparing it to continuous caloric restriction. Results were generally similar in terms of weight loss, although adherence profiles differ from person to person. It remains one of the best-documented forms of intermittent fasting in the clinical literature.