History of Intermittent Fasting: Origins to Now

The history of intermittent fasting stretches back thousands of years, long before it became a mainstream health topic. From ancient Greek philosophy and religious observances across Islam, Christianity, and Judaism, to twentieth-century medical research and the 2012 BBC documentary that brought the 5:2 diet to British households, fasting has evolved from a spiritual discipline into a widely discussed dietary strategy. This article traces that journey, examines the scientific evidence, outlines the most common methods used today, and explains who should approach intermittent fasting with caution.

Where did intermittent fasting originally come from?

Intermittent fasting originated in ancient religious and philosophical traditions, with figures such as Hippocrates advocating fasting for health and major world religions formalising it as a spiritual practice long before any scientific rationale was established.

Intermittent fasting has its earliest roots in ancient religious and philosophical traditions, predating formal medical understanding of nutrition by thousands of years. Across cultures and continents, periods of voluntary food restriction were woven into spiritual practice long before they were studied as a health intervention.

In ancient Greece, philosophers including Hippocrates and Pythagoras are widely attributed with advocating fasting as a means of mental clarity and physical purification, though primary texts are fragmentary and these attributions should be understood as part of a long-standing scholarly tradition rather than direct quotation. Hippocrates is often credited with the view that eating when ill could feed disease rather than the body, a sentiment that echoes in later medical thinking. Ancient Egyptian and Mesopotamian texts are also reported by historians of medicine to reference ritual fasting as a form of bodily and spiritual cleansing, though the evidence base for these claims is largely interpretive.

Religious traditions formalised these practices across the world. Islam prescribes Ramadan, a month of dawn-to-dusk fasting. Christianity has historically observed Lent and other fasting periods. Judaism marks Yom Kippur with a 25-hour fast. Hinduism and Buddhism both incorporate fasting days into their calendars. These traditions were not designed as weight-management tools, but they established a cultural familiarity with voluntary food restriction that would later inform secular health movements.

What is notable is that these early practices were largely intuitive, shaped by belief rather than physiology. The idea that the body might benefit metabolically from periods without food was not articulated in scientific terms until the twentieth century, yet the behavioural pattern itself is among the oldest documented human health practices.

How has intermittent fasting been used through the centuries?

Intermittent fasting has been used across the centuries as a religious observance, a Galenic medical remedy, and a naturopathic treatment, before attracting structured scientific investigation in the early twentieth century.

Intermittent fasting has been used across the centuries primarily as a religious observance, a medical remedy, and a philosophical discipline, with its application shifting considerably depending on the era and cultural context. Its journey from spiritual ritual to clinical investigation spans millennia.

During the medieval period in Europe, fasting was largely governed by the Catholic Church, which prescribed numerous fast days throughout the liturgical year. These were not optional for observant Christians, and historians of food culture have noted that the practice influenced agricultural patterns and trade. Physicians of the era, working within the Galenic tradition, also recommended fasting as a treatment for fevers and digestive complaints, believing it allowed the body to expel harmful humours, though these practices were not evaluated by modern standards of evidence.

By the eighteenth and nineteenth centuries, fasting began to attract secular medical interest. European physicians experimented with therapeutic fasting for conditions including obesity, epilepsy, and mental illness. In the United States, the naturopathic movement of the late nineteenth century promoted extended fasting as a means of detoxification, though these claims were rarely supported by rigorous evidence.

The early twentieth century saw more structured medical investigation. Researchers began documenting the physiological effects of caloric restriction and fasting on metabolism, laying groundwork for later scientific inquiry. By mid-century, fasting had largely fallen out of mainstream medical favour in Western countries, replaced by calorie-counting dietary approaches. However, interest never disappeared entirely, and it re-emerged with considerable force in the late twentieth and early twenty-first centuries as researchers began examining its effects on metabolic health, longevity, and chronic disease.

When did intermittent fasting become a recognised health approach in the UK?

Intermittent fasting became widely recognised in the UK after the 2012 BBC Horizon documentary introduced the 5:2 method; NICE and the NHS acknowledge it as one dietary option but have not formally endorsed it as a first-line strategy.

Intermittent fasting became widely recognised as a health approach in the UK following the broadcast of the BBC Horizon documentary "Eat, Fast and Live Longer" in 2012, presented by Dr Michael Mosley, which introduced the 5:2 method to a mainstream British audience. Before this point, intermittent fasting was largely confined to specialist research circles and niche health communities.

The documentary prompted significant public interest and was followed by the publication of "The Fast Diet" by Mosley and Mimi Spencer in 2013, which became a bestseller. This popularisation coincided with a growing body of peer-reviewed research examining the metabolic effects of time-restricted eating and periodic caloric restriction, giving the approach a degree of scientific credibility that earlier popular diet trends had lacked.

In the years that followed, NHS guidance and NICE did not formally endorse intermittent fasting as a first-line weight management strategy. NICE guidance on obesity management has continued to emphasise individualised dietary approaches, recognising that no single dietary method suits all patients, and NHS patient-facing resources have acknowledged intermittent fasting as one of several dietary patterns that some people find sustainable. NHS Live Well pages and the British Dietetic Association (BDA) have both provided balanced information on the approach.

By the late 2010s, intermittent fasting had moved from a fringe concept to a recognised, if not universally recommended, dietary strategy within UK health discourse. A number of UK universities and NHS-affiliated research groups have conducted or contributed to trials examining time-restricted eating and the 5:2 protocol, and the approach is now discussed in consultations about weight management and metabolic health, though clinical guidance continues to emphasise that it is not appropriate for everyone.

What does the scientific evidence say about intermittent fasting?

Evidence shows intermittent fasting can produce weight loss and improve metabolic markers, but produces results comparable to continuous caloric restriction when energy intake is matched, and NICE has not issued a specific recommendation in its favour.

The scientific evidence on intermittent fasting suggests it can support weight loss and improve certain metabolic markers in some individuals, though it does not appear to offer a consistent advantage over continuous caloric restriction when total energy intake is matched. Research in this area has grown substantially over the past two decades, though important questions remain.

Studies published in peer-reviewed journals, including trials conducted in the UK and internationally, have found that intermittent fasting can reduce body weight, improve insulin sensitivity, lower fasting glucose, and reduce inflammatory markers in some participants. A review by de Cabo and Mattson published in the New England Journal of Medicine in 2019 examined evidence across multiple fasting protocols and concluded that metabolic benefits were observed, particularly in people with overweight or obesity, though the authors noted that long-term adherence data remain limited. More recent systematic reviews and meta-analyses, including those published in journals such as JAMA and the BMJ, have broadly supported the finding that intermittent fasting produces weight loss comparable to continuous energy restriction when caloric intake is similarly controlled.

One area of active research is the effect of time-restricted eating on circadian biology. Evidence suggests that aligning food intake with daylight hours may have additional metabolic benefits beyond simple caloric restriction, though this remains an emerging field.^[5] Animal studies have shown promising results regarding longevity and cellular repair processes such as autophagy, but translating these findings to human clinical outcomes requires further investigation, and no firm conclusions can yet be drawn for people.^[2]

It is important to note that much of the existing evidence comes from relatively short-term trials with modest sample sizes. NICE has not issued specific guidance recommending intermittent fasting over other dietary approaches for weight management, reflecting the view that the evidence base, while encouraging, does not yet support a definitive clinical recommendation. The BDA provides a balanced summary of the evidence in its Intermittent Fasting Food Fact Sheet.^[13] Individuals considering intermittent fasting should discuss it with their GP or a registered dietitian, particularly if they have existing health conditions.

Which intermittent fasting methods are most commonly used today?

The most commonly used methods are the 5:2 protocol, 16:8 time-restricted eating, and alternate-day fasting, each differing in fasting frequency and duration, with no single approach suited to everyone.

The most commonly used intermittent fasting methods today are the 5:2 protocol, the 16:8 time-restricted eating approach, and alternate-day fasting, each differing in the frequency and duration of the fasting period. Understanding these distinctions helps individuals and clinicians assess which approach, if any, might be suitable.

The 5:2 method involves eating normally for five days of the week and restricting caloric intake to approximately 500 to 600 kilocalories (kcal) on two non-consecutive days.^[13] This was the approach popularised in the UK following the 2012 BBC documentary and remains widely recognised. The BDA notes that some versions of the protocol use sex-specific targets, and individuals should seek personalised advice.

The 16:8 method involves restricting all food intake to an eight-hour window each day and fasting for the remaining sixteen hours. Common eating windows include midday to 8 pm or 10 am to 6 pm, though the timing can be adjusted to suit individual circumstances. This approach is widely practised, partly because it requires no calorie counting, though it may not suit people who need to take medication with food or who are at risk of hypoglycaemia.

Alternate-day fasting involves alternating between days of normal eating and days of significant caloric restriction or complete fasting. Systematic reviews have reported that this approach tends to have a higher dropout rate in clinical trials compared with other protocols, suggesting it may be more demanding to sustain.^[3][4]

The 24-hour fast, sometimes called the eat-stop-eat method, involves one or two complete fasting days per week. This is less commonly used and requires careful consideration of individual health status.

All of these methods share the principle of creating periods of low or absent caloric intake, but they differ considerably in their practical demands. Adherence varies widely between individuals, and there is no single method that suits everyone. A GP or registered dietitian can help assess which approach, if any, is appropriate for a given person's health profile and lifestyle.

Is intermittent fasting safe, and who should avoid it?

Intermittent fasting is generally safe for healthy adults but should be avoided without medical supervision by those with insulin-treated diabetes, a history of eating disorders, pregnancy, frailty, or who take medicines affected by food intake.

Intermittent fasting is generally considered safe for healthy adults, but it is not appropriate for everyone, and certain groups should avoid it or seek medical advice before starting. Safety depends heavily on individual health status, existing medical conditions, and the specific fasting protocol chosen.

People who should avoid intermittent fasting without medical supervision include:

• Those with type 1 diabetes or insulin-treated type 2 diabetes, as fasting can increase the risk of hypoglycaemia and may require medication adjustment

• People taking SGLT2 inhibitors (such as dapagliflozin, empagliflozin, or canagliflozin), as prolonged fasting combined with reduced carbohydrate intake can increase the risk of euglycaemic diabetic ketoacidosis; anyone on these medicines should consult their GP or diabetes team before fasting

• Pregnant or breastfeeding women, for whom adequate and consistent nutrition is essential

• People with a history of eating disorders, including anorexia nervosa or bulimia, as restrictive eating patterns may trigger relapse

• Children and adolescents, whose nutritional needs during growth make caloric restriction potentially harmful

• People who are underweight or malnourished

• Frail older adults, who may be at increased risk of muscle loss and nutritional deficiency

• Those with advanced chronic kidney disease, where dietary management is already complex and should be supervised

• People with a history of gout, as fasting and rapid weight loss can precipitate flares

• Those taking medicines that must be taken with food, such as certain doses of rivaroxaban or other medicines where food affects absorption or tolerability; check with your GP or pharmacist before changing your eating pattern^[10][11]

For people with type 2 diabetes managed with diet or non-insulin medication, intermittent fasting may be considered under medical supervision, but any changes to eating patterns should be discussed with a GP or diabetes specialist first, as medication doses may need review. Diabetes UK provides guidance on fasting safely for people with diabetes.

Common side effects, particularly in the early weeks, include headaches, fatigue, irritability, difficulty concentrating, and disrupted sleep. These often settle as the body adapts. If you experience significant dizziness, fainting, or symptoms of hypoglycaemia, stop fasting, rehydrate, and contact your GP. For urgent advice, NHS 111 is available.

Anyone experiencing an adverse effect they believe may be related to a dietary supplement or product used alongside fasting can report it via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk. If you are considering intermittent fasting alongside any medical treatment, always consult your GP before making changes.

Scientific References

1. Overweight and obesity management (NG246) — Physical activity and diet.
2. Effects of Intermittent Fasting on Health, Aging, and Disease — de Cabo & Mattson.
3. Intermittent fasting for adults with overweight or obesity.
4. The impact of intermittent fasting on body composition and cardiometabolic outcomes in overweight and obese adults: a systematic review and meta-analysis of randomized controlled trials.
5. Time-Restricted Eating and Its Metabolic Benefits — Mishra et al..
6. SGLT2 inhibitors: updated advice on the risk of diabetic ketoacidosis.
7. Life-threatening dapagliflozin-associated euglycaemic diabetic ketoacidosis in a postoperative patient (BMJ Case Reports).
8. Low blood sugar (hypoglycaemia).
9. Efficacy and Safety of Intermittent Fasting in People With Insulin-Treated Type 2 Diabetes (INTERFAST-2) — A Randomized Controlled Trial (Diabetes Care).
10. Rivaroxaban (Xarelto▼): reminder that 15 mg and 20 mg tablets should be taken with food.
11. Rivaroxaban | Drugs | BNF — NICE.
12. Rivaroxaban Prescriber Guide (EMC).
13. All Food Fact Sheets — British Dietetic Association.
14. MHRA Yellow Card scheme — adverse event reports (FOI 21/1138).
15. Adverse reactions to drugs | Medicines guidance — BNF (NICE).
16. Intermittent fasting in the treatment of type 2 diabetes (Frontiers in Nutrition).
17. The effect of food on the absorption and pharmacokinetics of rivaroxaban — Stampfuss et al..

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