Fasting and Intermittent Fasting

01 Abstract

Human starvation physiology is an established sequence. After the last mixed meal, hepatic glycogen is drawn down over hours; lipolysis and fatty-acid oxidation rise; hepatic ketogenesis increases as the fast lengthens; gluconeogenesis from glycerol, lactate, and amino acids maintains glucose; protein loss is attenuated but not abolished; insulin falls and glucagon, catecholamines, and growth hormone rise in characteristic patterns (Cahill, 2006; Owen et al., 1969). That sequence is not a protocol menu. It is the background against which named fasting regimens must be read.

In free-living adults with overweight or obesity, intermittent-fasting regimens often produce weight loss similar to continuous caloric restriction when both reduce energy intake (Trepanowski et al., 2017; Harvie et al., 2011; Schübel et al., 2018). When a daily eating window is added without a prescribed deficit, some trials find little or no advantage over unrestricted eating (Lowe et al., 2020). When time-restricted eating is added to an explicit calorie target, a two-year randomised comparison did not show additional weight loss beyond calorie restriction alone (Liu et al., 2022). Isocaloric early time-restricted feeding can improve insulin sensitivity and blood pressure without further weight loss in short, tightly controlled designs (Sutton et al., 2018). That last result is a meal-timing finding. It is not evidence that sixteen hours of fasting “turns on autophagy” in human tissues, and it is not evidence that intermittent fasting extends human life.

The controlling conclusion of this article is therefore negative in the place the market is most confident, and limited in the place the physiology is most real. Fasting physiology is real. Named regimens are not interchangeable. After matching, intermittent fasting has not been shown to outperform continuous restriction for weight, fat mass, or most cardiometabolic endpoints. Early eating windows retain an independent glycaemic signal in some trials. Longevity, autophagy-as-consumer-benefit, and exact hour thresholds do not survive the human record.

The popular sentence is that intermittent fasting “works.” That sentence has no scientific content until the regimen, the comparator, the matching, the population, and the endpoint are named. Weight loss after an unmatched 5:2 diet is not the same finding as insulin sensitivity after isocaloric early time-restricted feeding, and neither is a human lifespan result.

The question this article answers is therefore not whether people can lose weight while eating less often. They can, as they can on any energy deficit. The question is: when calories, protein, weight loss, and diet quality are adequately matched, what human effects remain that can be attributed to fasting or to meal timing rather than to energy restriction — and for which named regimen? Continuous caloric restriction as a subject belongs to the sibling title SBL-41/SP-CALORIC-RESTRICTION. Here it is the comparator that decides whether a clock or a gap is doing independent work.

A second question is carried alongside the first because the market will not drop it: do autophagy, ketosis, or rodent longevity supply a human justification for a named hour-count? Those objects are treated separately in Part Four. They are not allowed to substitute for the matched-trial record in Part Three.

03 A taxonomy that must not collapse

The following names are used as they are used in the trial literature. They are not synonyms. An overnight fast is the default human condition of a nocturnal eating pause. Acute experimental fasting is a single, timed withholding, often 12–72 h, used to measure fuel fluxes (Cahill, 2006). Prolonged fasting, in the human clinical and spa literatures, is typically a multi-day food withdrawal, sometimes water-only and sometimes Broth-or-juice modified, often medically supervised (Wilhelmi de Toledo et al., 2019; Michalsen et al., 2005). Alternate-day fasting (ADF) alternates a zero- or near-zero-energy day with an ad libitum or controlled feast day (Heilbronn et al., 2005; Varady et al., 2013). Modified ADF allows a small intake — commonly about 25 per cent of energy needs — on the “fast” day (Trepanowski et al., 2017). The 5:2 pattern restricts energy on two non-consecutive days and leaves five days closer to habitual intake (Harvie et al., 2011). Periodic fasting names multi-day cycles repeated at intervals of weeks or months. Fasting-mimicking diets (FMD) are periodic, low-energy, low-protein, plant-formulated cycles designed to reproduce selected fasting responses without a water-only fast (Brandhorst et al., 2015; Wei et al., 2017). Time-restricted eating (TRE) confines the daily eating window, often to 4–12 h, without necessarily prescribing a calorie target (Gabel et al., 2018; Lowe et al., 2020). Early TRE (eTRE) places that window in the morning or early afternoon (Sutton et al., 2018; Jamshed et al., 2019). Late TRE places it in the afternoon or evening. Religious fasts, of which Ramadan is the most studied in metabolic journals, specify dawn-to-sunset abstinence with a nocturnal eating period; they are neither TRE nor ADF (Lessan and Ali, 2019).

Table 1. Fasting-regimen taxonomy used in this article. Cadences are typical of the trial literature, not prescriptions.

04 How the literature mixes protocols

Reviews that pool “intermittent fasting” as a single arm collapse ADF, 5:2, TRE, and sometimes FMD (de Cabo and Mattson, 2019; Patterson and Sears, 2017). Meta-analyses that do this can be useful for a first weight-loss estimate and misleading for mechanism. A TRE trial that does not prescribe a deficit is not a test of ADF. An FMD cycle is not a 16:8 window. Ramadan cohorts are observational, culturally specified, and usually include changes in sleep, hydration, and meal composition (Lessan and Ali, 2019). They cannot be spent as randomised TRE evidence.

The matching problem is the second mixing error. Many positive intermittent-fasting trials are unmatched: the fasting arm eats less because the protocol makes that easy, and the control arm is habitual intake (Gabel et al., 2018; Cienfuegos et al., 2020). That is a test of energy reduction delivered by a schedule, not a test of the schedule after energy is equated. The trials that do the harder work — Trepanowski et al. (2017) on modified ADF versus daily restriction; Schübel et al. (2018) in HELENA; Liu et al. (2022) on TRE plus calorie restriction; Sutton et al. (2018) on isocaloric eTRE — are the ones this article weights when the claim is independence from calories.

In humans, the post-absorptive state after a mixed meal is not a cliff. Hepatic glycogenolysis covers most of the overnight glucose requirement; as the fast lengthens, glycogen falls and gluconeogenesis and fatty-acid oxidation rise (Cahill, 2006; Rothman et al., 1991). Owen et al. (1969) measured, in prolonged starvation, the shift of glucose production toward kidney as well as liver and the rising contribution of ketone bodies to brain fuel. Those classic studies describe days, not a 16:8 window. Treating an overnight fast as if it were Cahill starvation is a category error.

Insulin falls as glucose and incretin drive recede. Glucagon, catecholamines, and growth hormone rise in patterns that support lipolysis and hepatic glucose output (Heilbronn et al., 2005; Anton et al., 2018). Growth-hormone pulses during fasting are a human endocrine finding; they are not a hypertrophy protocol and they do not license unsupervised multi-day fasts. Protein oxidation continues. The body attenuates nitrogen loss as ketones rise, but it does not stop losing lean tissue (Cahill, 2006). That fact is the physiological ground of the lean-mass concern in Part Three.

06 Glycogen, lipolysis, fatty-acid oxidation, ketogenesis

Human ¹³C NMR work showed that hepatic glycogen is substantially depleted over about a day of fasting, with gluconeogenesis already contributing a large fraction of glucose production before glycogen is gone (Rothman et al., 1991). Muscle glycogen is a different store, more tightly tied to recent carbohydrate and contractile work. Lipolysis increases as insulin falls and catecholamine sensitivity of adipose tissue changes (Jensen et al., 1987). Fatty acids are oxidised in liver and muscle; the liver converts a fraction to ketone bodies. Ketogenesis is therefore a function of fatty-acid supply, hepatic carbohydrate status, and insulin — not a switch that flips at a marketed hour.

Ketosis is established as a metabolic state of prolonged carbohydrate and energy deficit. It is not a validated surrogate for weight-independent health benefit. People on a late eating window can be post-absorptive at dawn without being in starvation ketosis. People on a ketogenic diet can be ketotic while eating. The state and the intervention are not the same object.

07 Protein metabolism, insulin, glucagon, catecholamines, growth hormone

During a fast, whole-body protein breakdown supplies gluconeogenic amino acids. The rate falls as ketone use rises, but nitrogen balance remains negative until food returns (Cahill, 2006). Resistance training and adequate protein on feeding days are the usual experimental attempts to protect fat-free mass; they are not guaranteed by the fast itself (Moro et al., 2016; Tinsley et al., 2017). Insulin suppression is the endocrine signature of the post-absorptive state. Glucagon supports hepatic glucose output. Catecholamines support lipolysis. Growth hormone rises with fasting in human studies and participates in the lipolytic and anti-insulin milieu (Anton et al., 2018). None of these hormone changes, by themselves, constitute a clinical outcome.

08 AMPK, mTOR, and autophagy as measured objects

AMPK is activated by a falling energy charge; mTORC1 is restrained when amino acids and insulin-pathway input fall (Hardie, 2005; Wolfson et al., 2016). Autophagy is the conserved recycling programme that those and other inputs regulate. In yeast and in mice, nutrient withdrawal induces autophagy that can be measured with LC3, p62, and genetic reporters (Kuma et al., 2004; Alirezaei et al., 2010). Alirezaei et al. (2010) reported profound neuronal autophagy in mice after short-term fasting. That is a mouse-brain finding. It is not a demonstration that a human 16:8 window clears human neurons.

Human evidence that everyday intermittent fasting “turns on autophagy” in a tissue that matters for aging is thin. Blood-cell LC3 changes, if present, are not organ autophagy. Ketone appearance is not an autophagy assay. The consumer claim that a specific clock hour is required is speculative and is red-teamed in Part Four. What is established is the signalling logic in cells and animals. What is not established is a human, regimen-specific, outcome-linked autophagy dose.

09 Circadian biology and meal timing

Peripheral clocks in liver and adipose tissue are reset by food as well as by light (Chaix et al., 2014; Panda, 2016). In mice, time-restricted feeding can improve metabolic measures even when calories are not reduced (Hatori et al., 2012; Chaix et al., 2014). That animal result is the origin of much TRE optimism. It is also the origin of over-read. Mice are nocturnal; a “daytime” feeding window in a mouse is not an early human breakfast window.

In humans, early eating windows can improve 24-hour glucose and some insulin measures relative to later windows in controlled designs (Sutton et al., 2018; Jamshed et al., 2019; Hutchison et al., 2019). The American Heart Association scientific statement on meal timing treated frequency and timing as plausible cardiovascular modifiers, not as proven event-reducing therapies (St-Onge et al., 2017). Circadian alignment is therefore a real axis. It is not a substitute for energy balance, and it is not a licence to treat late TRE as metabolically equivalent to eTRE.

A fasting regimen can reduce intake by shrinking the number of eating occasions, or it can fail because feast days or nocturnal meals compensate. Heilbronn et al. (2005) found, in non-obese adults on ADF, that feast-day intake did not fully replace the fast-day deficit, so weight fell. That is a human compensation finding, not a universal law. TRE trials that do not prescribe calories sometimes report spontaneous energy reduction and sometimes do not (Gabel et al., 2018; Lowe et al., 2020). Hunger on fast days is a common reason for dropout (Trepanowski et al., 2017). Appetite is therefore both a mechanism of deficit and a mechanism of non-adherence. It is not, by itself, a health outcome.

11 Weight loss when calories are not matched

In adults with overweight or obesity, unmatched intermittent-energy-restriction and TRE protocols often produce weight loss of a few kilograms over weeks to months, in the same range as other diet advice that reduces energy (Harris et al., 2018; Rynders et al., 2019; Patikorn et al., 2021). Gabel et al. (2018) reported weight loss with 8-hour TRE against a historical no-intervention frame. Cienfuegos and colleagues later tested shorter windows. These designs answer “does this schedule reduce weight versus usual eating?” They do not answer the controlling question. An umbrella review of meta-analyses found benefits for weight and some metabolic markers, with the usual caveats of short duration, heterogeneous protocols, and overlapping trials (Patikorn et al., 2021).

12 The calorie-matched comparator

Trepanowski et al. (2017) randomised adults with obesity to modified ADF, daily calorie restriction, or control for a year. Weight loss did not differ significantly between ADF and daily restriction; LDL cholesterol rose in the ADF arm relative to daily restriction in that report; dropout was high. Catenacci et al. (2016), in a smaller zero-calorie ADF versus daily restriction pilot, likewise found similar weight change. Harvie et al. (2013) compared intermittent energy and carbohydrate restriction with daily restriction in overweight women and reported similar weight loss with some insulin-marker differences that did not rewrite the weight result. HELENA was designed to test intermittent versus continuous restriction at equal net intake (Schübel et al., 2016). Across this class of trials, the repeating human result is strongly supported: when the energy gap is similar, intermittent schedules do not reliably outperform daily restriction for weight.

Liu et al. (2022) randomised adults with obesity to calorie restriction with or without an eight-hour eating window for 12 months. Time restriction did not add weight loss beyond the calorie target. Templeman et al. (2021) isolated 24-hour fasting from energy restriction in lean adults: alternate-day 24-hour fasts with 150 per cent intake on feeding days were compared with matched continuous restriction and with a control. Fasting without a net deficit did not reproduce the metabolic signature of energy restriction. Those two trials, with Trepanowski et al. (2017), are the core of the matched-comparator case.

13 Time-restricted eating: window versus clock

Lowe et al. (2020) prescribed a 12:8 to 16:8-style window without calorie counselling and found no meaningful weight advantage over a three-meal pattern in a randomised design with objective weighing in a subset. Sutton et al. (2018), by contrast, fed men with prediabetes an early time-restricted schedule that was isocaloric and still improved insulin sensitivity, blood pressure, and oxidative-stress markers without weight loss. Jamshed et al. (2019) reported improved 24-hour glucose on early restricted feeding. Hutchison et al. (2019) found improved glucose tolerance with time-restricted feeding in men at risk for type 2 diabetes. These eTRE results are the strongest human case for an independent timing effect on glycaemia. They are short, small, and tightly controlled. They do not show that any window of the same length works, and they do not show event reduction.

Late TRE is not the same experiment. Eating the day’s energy at night sits closer to circadian misalignment. Ramadan CGM work shows large dusk excursions and overnight hyperglycaemia when the fast is broken with a large meal (Lessan et al., 2012; Lessan et al., 2015). That is religious fasting physiology, not a refutation of morning eTRE, and not a reason to treat Ramadan as a TRE trial.

14 Glucose, insulin, lipids, blood pressure, inflammation, liver fat

When weight falls, fasting glucose, insulin, and triglycerides often improve, as they do in any successful energy-restriction trial (Harris et al., 2018; Rynders et al., 2019). After matching, the incremental IF effect on those endpoints is inconsistent. Sutton et al. (2018) is the main isocaloric exception for insulin sensitivity and blood pressure. Lipids are mixed: some ADF reports raise LDL (Trepanowski et al., 2017); others do not. Inflammatory markers and liver fat generally move with weight and with diet quality; they have not been shown, in adequately matched human trials, to be unique signatures of a 16:8 clock. Cardiovascular events have not been tested in a powered IF outcomes trial. The AHA meal-timing statement did not convert timing into a substitute for established risk-factor care (St-Onge et al., 2017).

15 Body composition and lean mass

Fat mass falls when energy intake falls. Fat-free mass often falls with it. Whether IF accelerates lean loss relative to daily restriction is not settled. Resistance-trained men on 16:8 TRE with protein-aware eating preserved strength and lean mass over eight weeks in Moro et al. (2016). Tinsley et al. (2017) found more ambiguous body-composition results in a shorter TRE-plus-training design. In untrained or older adults, a protein gap on feeding days is a plausible harm pathway and is not disproven by athlete studies. The honest grade is emerging and population-specific: training and protein can protect lean mass on TRE; IF is not a lean-mass-sparing technology.

16 Exercise

Training in the fasted state changes substrate use; it does not automatically improve performance. Athlete TRE studies are small and mixed (Moro et al., 2016; Tinsley et al., 2017). Ramadan research in athletes is a different literature, complicated by dehydration and sleep. This article does not extract an exercise prescription. It records that exercise is a modifier of body composition and glycaemia under any diet, and that fasted training is not a validated longevity intervention.

The consumer sentence is that a 16-hour fast “turns on autophagy.” The laboratory sentence is that nutrient withdrawal induces autophagy in yeast, cultured cells, and mice, including mouse neurons after short fasts (Alirezaei et al., 2010). Those sentences are not interchangeable. Human tissues of interest — liver, muscle, brain — are not routinely biopsied for LC3 flux in TRE trials. Blood-cell markers, when collected, are not organ autophagy. Ketone appearance is not an autophagy assay. A marketed hour-count has not been calibrated against a human flux measurement that predicts a clinical outcome.

Grade: autophagy as a conserved starvation response in cells and animals is established. Autophagy as a proven, hour-thresholded, consumer benefit of 16:8 practice is speculative. The dedicated red-team file in the apparatus records this ruling: keep the cell biology; drop the hour-switch.

18 Exact fasting hours

Glycogen NMR and starvation studies describe a continuous shift, not a cliff at 12, 14, 16, or 18 hours (Rothman et al., 1991; Cahill, 2006). TRE trials use windows of 4, 6, 8, 10, or 12 hours for operational convenience (Gabel et al., 2018; Wilkinson et al., 2020). Sutton et al. (2018) used an early six-hour window because that was the experimental meal schedule, not because a receptor times out at hour six. The claim that a specific hour is required for benefit is not established in humans. What is established is that longer daily fasts often reduce eating occasions, and that early placement can change glycaemia in controlled feeding.

19 Ketosis as a proxy for benefit

Ketone concentrations rise as hepatic carbohydrate status falls and fatty-acid supply rises. That is chemistry. It is not a clinical endpoint. People can lose weight without measurable ketosis. People can be ketotic on a high-fat diet while gaining weight. Prolonged-fast ketosis is not 16:8 ketosis. Using a urine strip as a success metric for intermittent fasting confuses a fuel shift with an outcome. Grade: ketosis as a fasting metabolite is established; ketosis as a sufficient proxy for benefit is speculative.

20 Longevity and rodent extrapolation

Caloric restriction extends life in many laboratory animals. Every-other-day feeding and time-restricted feeding can extend life or improve metabolic disease in mice, sometimes even without a calorie cut (Hatori et al., 2012; Mitchell et al., 2019). Pak et al. (2021) argued, in mice, that fasting periods mediate much of the geroprotective effect of a calorie-restricted diet. Those are mouse findings. Human CALERIE tested two years of calorie restriction in non-obese adults and improved cardiometabolic risk factors and some aging biomarkers; it did not measure lifespan (Ravussin et al., 2015; Kraus et al., 2019). No human randomised trial of intermittent fasting has a mortality endpoint. Observational periodic-fasting reports cannot carry that load. FMD cycles improved selected risk markers in a small human study (Wei et al., 2017) and produced multi-system effects in mice (Brandhorst et al., 2015). That is not a human longevity trial.

The sibling CR article owns the continuous-restriction lifespan debate. This title’s ruling is narrower: human intermittent fasting has insufficient evidence for lifespan extension. Rodent ADF and TRE longevity are not transferable by assertion. de Cabo and Mattson (2019) reviewed the animal and human literatures together; the present article refuses to let the animal half settle the human half.

21 Fasting independent of calorie reduction

After matching, the surviving independent effects are limited. Sutton et al. (2018) and related eTRE work show glycaemic and blood-pressure changes without further weight loss. Templeman et al. (2021) show that fasting without a net deficit is not a substitute for energy restriction in lean adults. Liu et al. (2022) and Trepanowski et al. (2017) show that adding a schedule to a matched energy gap does not reliably enlarge weight loss. The red-team ruling: do not claim a general calorie-independent benefit. Claim, at most, a timing effect on selected glycaemic measures in early-window, tightly controlled human studies.

22 Adherence as an independent virtue

Some participants prefer fewer eating occasions. Some drop out because of hunger on fast days (Trepanowski et al., 2017). Lowe et al. (2020) did not find an adherence miracle. Preference is real and individual. It is not evidence that intermittent fasting is easier in general, and it is not evidence that easier-for-some is a biological advantage after matching. Grade: adherence advantage is plausible for some people and not established as a class property.

23 Long-term outcome evidence

Most human IF trials last weeks to one year. Cardiovascular events, cancer incidence, dementia, and death are not powered endpoints. CALERIE is the longest high-quality human restriction trial and is not an IF trial (Kraus et al., 2019). Wilkinson et al. (2020) showed 10-hour TRE improvements in a metabolic-syndrome cohort without a calorie-matched control of the same intensity. The long-term outcome grade for intermittent fasting as a disease-modifying therapy is not established.

The trial corpus is concentrated in adults with overweight or obesity, often middle-aged, often without frailty or pregnancy. That sampling is not an accident and it is not a licence to generalise.

Pregnancy and lactation. Energy and micronutrient needs are higher. Intermittent fasting is not an evidence-based prenatal intervention in this corpus. Religious fasting in pregnancy is a clinical and cultural question outside a lifestyle-trial dataset. This document recommends no regimen.

Children and adolescents. Growth, energy, and eating-disorder risk make recreational IF inappropriate as a research-supported practice. Ganson and related adolescent survey work sits beside, not inside, the adult RCT record. Cuccolo et al. (2022) associated intermittent-fasting implementation with eating-disorder symptomatology in a surveyed sample — an observational warning, not a causal trial.

Older adults and frailty. Lean-mass loss, polypharmacy, and falls risk make unmatched energy restriction a different object than it is in a 35-year-old. Protein and resistance training matter more here, not less (see the sibling amino-acid and nutrition-for-aging titles). TRE in older adults has been piloted; it is not a frailty therapy.

Athletes. Small TRE-plus-training studies do not underwrite a performance protocol (Moro et al., 2016; Tinsley et al., 2017). Fasted endurance sessions change fuel use. They do not automatically improve race outcomes.

Diabetes and medications. Ramadan CGM studies document large glucose swings when meals shift to night (Lessan et al., 2012; Lessan et al., 2015). Insulin, sulfonylureas, and SGLT2 inhibitors change hypoglycaemia and volume-depletion risk when meals are skipped. A few TRE feasibility studies exist in type 2 diabetes. They are not a substitute for individual clinical management, which this document does not provide.

Other medications. Time-of-day dosing, food effects on absorption, and hypotension on prolonged fasts (including medically supervised water-only series such as Goldhamer et al., 2001) are safety objects, not lifestyle tips.

25 Eating-disorder risk, frailty, and the residual clinical question

Any protocol that moralises hunger or valorizes going without food can be recruited by disordered eating. That is not a reason to pretend the metabolic literature does not exist. It is a reason not to market hour-counts to adolescents or to people with a restricting history (Cuccolo et al., 2022). Prolonged water-only fasting has blood-pressure effects in selected supervised series (Goldhamer et al., 2001); it is not 16:8, and it is not a home protocol in this document.

What remains after matching, taxonomy, and safety is modest. Intermittent fasting can be a way some adults reduce energy intake. Early eating windows can improve some glycaemic measures in short, controlled studies without further weight loss. Autophagy marketing, exact hours, ketosis-as-victory, rodent longevity, and a general calorie-independent benefit do not survive. Continuous restriction, diet quality, protein, and training remain the objects that actually move weight and lean mass in the matched record. This title does not tell a reader what to eat or when. It tells a reader what the names mean and what the trials have and have not shown.

The numbered list is generated from verified NCBI records in the 20 August 2026 search. Identifiers that could not be resolved were not printed. Author–year citations in the text correspond to this list.

1. Alirezaei M, Kemball CC, Flynn CT, Wood MR, Whitton JL, Kiosses WB. Short-term fasting induces profound neuronal autophagy. Autophagy. 2010;6(6):702-10.
   PMID 20534972 · PMC3106288 · doi:10.4161/auto.6.6.12376
2. Anton SD, Moehl K, Donahoo WT, Marosi K, Lee SA, Mainous AG, et al.. Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Obesity (Silver Spring, Md.). 2018;26(2):254-268.
   PMID 29086496 · PMC5783752 · doi:10.1002/oby.22065
3. Brandhorst S, Choi IY, Wei M, Cheng CW, Sedrakyan S, Navarrete G, et al.. A Periodic Diet that Mimics Fasting Promotes Multi-System Regeneration, Enhanced Cognitive Performance, and Healthspan. Cell metabolism. 2015;22(1):86-99.
   PMID 26094889 · PMC4509734 · doi:10.1016/j.cmet.2015.05.012
4. Cahill GF. Fuel metabolism in starvation. Annual review of nutrition. 2006;26:1-22.
   PMID 16848698 · doi:10.1146/annurev.nutr.26.061505.111258
5. Catenacci VA, Pan Z, Ostendorf D, Brannon S, Gozansky WS, Mattson MP, et al.. A randomized pilot study comparing zero-calorie alternate-day fasting to daily caloric restriction in adults with obesity. Obesity (Silver Spring, Md.). 2016;24(9):1874-83.
   PMID 27569118 · PMC5042570 · doi:10.1002/oby.21581
6. Chaix A, Zarrinpar A, Miu P, Panda S. Time-restricted feeding is a preventative and therapeutic intervention against diverse nutritional challenges. Cell metabolism. 2014;20(6):991-1005.
   PMID 25470547 · PMC4255155 · doi:10.1016/j.cmet.2014.11.001
7. Cuccolo K, Kramer R, Petros T, Thoennes M. Intermittent fasting implementation and association with eating disorder symptomatology. Eating disorders. 2022;30(5):471-491.
   PMID 34191688 · doi:10.1080/10640266.2021.1922145
8. Felig P, Marliss E, Owen OE, Cahill GF. Blood glucose and cluconeogenesis in fasting man. Archives of internal medicine. 1969;123(3):293-8.
   PMID 4885676
9. Fond G, Macgregor A, Leboyer M, Michalsen A. Fasting in mood disorders: neurobiology and effectiveness. A review of the literature. Psychiatry research. 2013;209(3):253-8.
   PMID 23332541 · doi:10.1016/j.psychres.2012.12.018
10. Fontana L, Meyer TE, Klein S, Holloszy JO. Long-term calorie restriction is highly effective in reducing the risk for atherosclerosis in humans. Proceedings of the National Academy of Sciences of the United States of America. 2004;101(17):6659-63.
    PMID 15096581 · PMC404101 · doi:10.1073/pnas.0308291101
11. Gabel K, Varady KA. Intermittent Fasting and Muscle Lipid Metabolism. The Journal of clinical endocrinology and metabolism. 2021;106(3):e1468-e1470.
    PMID 33169157 · doi:10.1210/clinem/dgaa818
12. Goldhamer A, Lisle D, Parpia B, Anderson SV, Campbell TC. Medically supervised water-only fasting in the treatment of hypertension. Journal of manipulative and physiological therapeutics. 2001;24(5):335-9.
    PMID 11416824 · doi:10.1067/mmt.2001.115263
13. Green CL, Englund DA, Das S, Herrerias MM, Yousefzadeh MJ, Grant RA, et al.. The Second Annual Symposium of the Midwest Aging Consortium: The Future of Aging Research in the Midwestern United States. The journals of gerontology. Series A, Biological sciences and medical sciences. 2021;76(12):2156-2161.
    PMID 34323268 · PMC8599030 · doi:10.1093/gerona/glab210
14. Halberg N, Henriksen M, Söderhamn N, Stallknecht B, Ploug T, Schjerling P, et al.. Effect of intermittent fasting and refeeding on insulin action in healthy men. Journal of applied physiology (Bethesda, Md. : 1985). 2005;99(6):2128-36.
    PMID 16051710 · doi:10.1152/japplphysiol.00683.2005
15. Hardie DG. New roles for the LKB1-->AMPK pathway. Current opinion in cell biology. 2005;17(2):167-73.
    PMID 15780593 · doi:10.1016/j.ceb.2005.01.006
16. Harris L, Hamilton S, Azevedo LB, Olajide J, De Brún C, Waller G, et al.. Intermittent fasting interventions for treatment of overweight and obesity in adults: a systematic review and meta-analysis. JBI database of systematic reviews and implementation reports. 2018;16(2):507-547.
    PMID 29419624 · doi:10.11124/JBISRIR-2016-003248
17. Harvie M, Wright C, Pegington M, McMullan D, Mitchell E, Martin B, et al.. The effect of intermittent energy and carbohydrate restriction v. daily energy restriction on weight loss and metabolic disease risk markers in overweight women. The British journal of nutrition. 2013;110(8):1534-47.
    PMID 23591120 · PMC5857384 · doi:10.1017/S0007114513000792
18. Hatori M, Vollmers C, Zarrinpar A, DiTacchio L, Bushong EA, Gill S, et al.. Time-restricted feeding without reducing caloric intake prevents metabolic diseases in mice fed a high-fat diet. Cell metabolism. 2012;15(6):848-60.
    PMID 22608008 · PMC3491655 · doi:10.1016/j.cmet.2012.04.019
19. Heilbronn LK, Smith SR, Martin CK, Anton SD, Ravussin E. Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism. The American journal of clinical nutrition. 2005;81(1):69-73.
    PMID 15640462 · doi:10.1093/ajcn/81.1.69
20. Hutchison AT, Liu B, Wood RE, Vincent AD, Thompson CH, O'Callaghan NJ, et al.. Effects of Intermittent Versus Continuous Energy Intakes on Insulin Sensitivity and Metabolic Risk in Women with Overweight. Obesity (Silver Spring, Md.). 2019;27(1):50-58.
    PMID 30569640 · doi:10.1002/oby.22345
21. Jamshed H, Beyl RA, Della Manna DL, Yang ES, Ravussin E, Peterson CM. Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in Humans. Nutrients. 2019;11(6).
    PMID 31151228 · PMC6627766 · doi:10.3390/nu11061234
22. Jensen MD, Haymond MW, Gerich JE, Cryer PE, Miles JM. Lipolysis during fasting. Decreased suppression by insulin and increased stimulation by epinephrine. The Journal of clinical investigation. 1987;79(1):207-13.
    PMID 3540009 · PMC424023 · doi:10.1172/JCI112785
23. Klempel MC, Kroeger CM, Varady KA. Alternate day fasting (ADF) with a high-fat diet produces similar weight loss and cardio-protection as ADF with a low-fat diet. Metabolism: clinical and experimental. 2013;62(1):137-43.
    PMID 22889512 · doi:10.1016/j.metabol.2012.07.002
24. Kraus WE, Bhapkar M, Huffman KM, Pieper CF, Krupa Das S, Redman LM, et al.. 2 years of calorie restriction and cardiometabolic risk (CALERIE): exploratory outcomes of a multicentre, phase 2, randomised controlled trial. The lancet. Diabetes & endocrinology. 2019;7(9):673-683.
    PMID 31303390 · PMC6707879 · doi:10.1016/S2213-8587(19)30151-2
25. Kroeger CM, Trepanowski JF, Klempel MC, Barnosky A, Bhutani S, Gabel K, et al.. Eating behavior traits of successful weight losers during 12 months of alternate-day fasting: An exploratory analysis of a randomized controlled trial. Nutrition and health. 2018;24(1):5-10.
    PMID 29353535 · PMC7183822 · doi:10.1177/0260106017753487
26. Lessan N, Hasan H, Barakat MT. Ramadan fasting: a study of changes in glucose profiles among patients with diabetes using continuous glucose monitoring. Diabetes care. 2012;35(5):e37.
    PMID 22517945 · PMC3329831 · doi:10.2337/dc11-2037
27. Lessan N, Hannoun Z, Hasan H, Barakat MT. Glucose excursions and glycaemic control during Ramadan fasting in diabetic patients: insights from continuous glucose monitoring (CGM). Diabetes & metabolism. 2015;41(1):28-36.
    PMID 25497966 · doi:10.1016/j.diabet.2014.11.004
28. Longo VD, Fontana L. Calorie restriction and cancer prevention: metabolic and molecular mechanisms. Trends in pharmacological sciences. 2010;31(2):89-98.
    PMID 20097433 · PMC2829867 · doi:10.1016/j.tips.2009.11.004
29. Lowe DA, Wu N, Rohdin-Bibby L, Moore AH, Kelly N, Liu YE, et al.. Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity: The TREAT Randomized Clinical Trial. JAMA internal medicine. 2020;180(11):1491-1499.
    PMID 32986097 · PMC7522780 · doi:10.1001/jamainternmed.2020.4153
30. Manoogian ENC, Panda S. Circadian rhythms, time-restricted feeding, and healthy aging. Ageing research reviews. 2017;39:59-67.
    PMID 28017879 · PMC5814245 · doi:10.1016/j.arr.2016.12.006
31. Mattison JA, Colman RJ, Beasley TM, Allison DB, Kemnitz JW, Roth GS, et al.. Caloric restriction improves health and survival of rhesus monkeys. Nature communications. 2017;8:14063.
    PMID 28094793 · PMC5247583 · doi:10.1038/ncomms14063
32. Mattson MP, Longo VD, Harvie M. Impact of intermittent fasting on health and disease processes. Ageing research reviews. 2017;39:46-58.
    PMID 27810402 · PMC5411330 · doi:10.1016/j.arr.2016.10.005
33. Mitchell SJ, Bernier M, Mattison JA, Aon MA, Kaiser TA, Anson RM, et al.. Daily Fasting Improves Health and Survival in Male Mice Independent of Diet Composition and Calories. Cell metabolism. 2019;29(1):221-228.e3.
    PMID 30197301 · PMC6326845 · doi:10.1016/j.cmet.2018.08.011
34. Moro T, Tinsley G, Bianco A, Marcolin G, Pacelli QF, Battaglia G, et al.. Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males. Journal of translational medicine. 2016;14(1):290.
    PMID 27737674 · PMC5064803 · doi:10.1186/s12967-016-1044-0
35. Patikorn C, Roubal K, Veettil SK, Chandran V, Pham T, Lee YY, et al.. Intermittent Fasting and Obesity-Related Health Outcomes: An Umbrella Review of Meta-analyses of Randomized Clinical Trials. JAMA network open. 2021;4(12):e2139558.
    PMID 34919135 · PMC8683964 · doi:10.1001/jamanetworkopen.2021.39558
36. Patterson RE, Laughlin GA, LaCroix AZ, Hartman SJ, Natarajan L, Senger CM, et al.. Intermittent Fasting and Human Metabolic Health. Journal of the Academy of Nutrition and Dietetics. 2015;115(8):1203-12.
    PMID 25857868 · PMC4516560 · doi:10.1016/j.jand.2015.02.018
37. Piacenza F, Malavolta M, Basso A, Costarelli L, Giacconi R, Ravussin E, et al.. Effect of 6-month caloric restriction on Cu bound to ceruloplasmin in adult overweight subjects. The Journal of nutritional biochemistry. 2015;26(8):876-82.
    PMID 26001545 · PMC4469556 · doi:10.1016/j.jnutbio.2015.03.012
38. Rothman DL, Magnusson I, Katz LD, Shulman RG, Shulman GI. Quantitation of hepatic glycogenolysis and gluconeogenesis in fasting humans with 13C NMR. Science (New York, N.Y.). 1991;254(5031):573-6.
    PMID 1948033 · doi:10.1126/science.1948033
39. Rynders CA, Thomas EA, Zaman A, Pan Z, Catenacci VA, Melanson EL. Effectiveness of Intermittent Fasting and Time-Restricted Feeding Compared to Continuous Energy Restriction for Weight Loss. Nutrients. 2019;11(10).
    PMID 31614992 · PMC6836017 · doi:10.3390/nu11102442
40. Schübel R, Graf ME, Nattenmüller J, Nabers D, Sookthai D, Gruner LF, et al.. The effects of intermittent calorie restriction on metabolic health: Rationale and study design of the HELENA Trial. Contemporary clinical trials. 2016;51:28-33.
    PMID 27687742 · doi:10.1016/j.cct.2016.09.004
41. Solon-Biet SM, Mitchell SJ, de Cabo R, Raubenheimer D, Le Couteur DG, Simpson SJ. Macronutrients and caloric intake in health and longevity. The Journal of endocrinology. 2015;226(1):R17-28.
    PMID 26021555 · PMC4490104 · doi:10.1530/JOE-15-0173
42. St-Onge MP, Ard J, Baskin ML, Chiuve SE, Johnson HM, Kris-Etherton P, et al.. Meal Timing and Frequency: Implications for Cardiovascular Disease Prevention: A Scientific Statement From the American Heart Association. Circulation. 2017;135(9):e96-e121.
    PMID 28137935 · PMC8532518 · doi:10.1161/CIR.0000000000000476
43. Stekovic S, Hofer SJ, Tripolt N, Aon MA, Royer P, Pein L, et al.. Alternate Day Fasting Improves Physiological and Molecular Markers of Aging in Healthy, Non-obese Humans. Cell metabolism. 2019;30(3):462-476.e6.
    PMID 31471173 · doi:10.1016/j.cmet.2019.07.016
44. Sutton EF, Beyl R, Early KS, Cefalu WT, Ravussin E, Peterson CM. Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes. Cell metabolism. 2018;27(6):1212-1221.e3.
    PMID 29754952 · PMC5990470 · doi:10.1016/j.cmet.2018.04.010
45. Templeman I, Smith HA, Chowdhury E, Chen YC, Carroll H, Johnson-Bonson D, et al.. A randomized controlled trial to isolate the effects of fasting and energy restriction on weight loss and metabolic health in lean adults. Science translational medicine. 2021;13(598).
    PMID 34135111 · doi:10.1126/scitranslmed.abd8034
46. Tinsley GM, Forsse JS, Butler NK, Paoli A, Bane AA, La Bounty PM, et al.. Time-restricted feeding in young men performing resistance training: A randomized controlled trial. European journal of sport science. 2017;17(2):200-207.
    PMID 27550719 · doi:10.1080/17461391.2016.1223173
47. Trepanowski JF, Kroeger CM, Barnosky A, Klempel MC, Bhutani S, Hoddy KK, et al.. Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults: A Randomized Clinical Trial. JAMA internal medicine. 2017;177(7):930-938.
    PMID 28459931 · PMC5680777 · doi:10.1001/jamainternmed.2017.0936
48. Varady KA, Cienfuegos S, Ezpeleta M, Gabel K. Clinical application of intermittent fasting for weight loss: progress and future directions. Nature reviews. Endocrinology. 2022;18(5):309-321.
    PMID 35194176 · doi:10.1038/s41574-022-00638-x
49. Wilhelmi de Toledo F, Buchinger A, Burggrabe H, Hölz G, Kuhn C, Lischka E, et al.. Fasting therapy - an expert panel update of the 2002 consensus guidelines. Forschende Komplementarmedizin (2006). 2013;20(6):434-43.
    PMID 24434758 · doi:10.1159/000357602
50. Wilkinson MJ, Manoogian ENC, Zadourian A, Lo H, Fakhouri S, Shoghi A, et al.. Ten-Hour Time-Restricted Eating Reduces Weight, Blood Pressure, and Atherogenic Lipids in Patients with Metabolic Syndrome. Cell metabolism. 2020;31(1):92-104.e5.
    PMID 31813824 · PMC6953486 · doi:10.1016/j.cmet.2019.11.004
51. Wolfson RL, Chantranupong L, Saxton RA, Shen K, Scaria SM, Cantor JR, et al.. Sestrin2 is a leucine sensor for the mTORC1 pathway. Science (New York, N.Y.). 2016;351(6268):43-8.
    PMID 26449471 · PMC4698017 · doi:10.1126/science.aab2674
52. Zarrinpar A, Chaix A, Panda S. Daily Eating Patterns and Their Impact on Health and Disease. Trends in endocrinology and metabolism: TEM. 2016;27(2):69-83.
    PMID 26706567 · PMC5081399 · doi:10.1016/j.tem.2015.11.007
53. Zhao L, Hutchison AT, Liu B, Yates CL, Teong XT, Wittert GA, et al.. Time-restricted eating improves glycemic control and dampens energy-consuming pathways in human adipose tissue. Nutrition (Burbank, Los Angeles County, Calif.). 2022;96:111583.
    PMID 35150947 · doi:10.1016/j.nut.2021.111583

27 Evidence handling

Study type is labelled in the reporting sentence. Animal and in-vitro results are never phrased as human outcomes. Unmatched intake reduction is not treated as a meal-timing effect. Ketone concentrations, autophagy markers, and rodent lifespan are treated as different objects from human clinical endpoints. When a newer matched null and an older unmatched positive conflict, both are kept and the matching difference is named. Religious fasting is not recoded as TRE. Project 06 was queried read-only; its hits were dominated by autophagy ontology and general textbooks, not by the IF trial corpus, and were used as orientation only. 07_Peptide_News was not reachable in this session (PostgreSQL client missing) and is not scientific evidence in any case.

28 Limitations and sibling titles

This is a scientific article, not a registered systematic review. Coverage is deep on taxonomy, starvation physiology, matched versus unmatched trials, eTRE, and the named marketing claims, and thinner on paediatric field data and every religious calendar other than Ramadan. Several landmark HELENA outcome papers and some 5:2 trials were sought in the reviewed record; where a specific result paper was not in the verified store, the design paper or a neighbouring verified trial is cited instead of an invented identifier. The literature was searched on 20 August 2026. Continuous caloric restriction as a subject is owned by SBL-41/SP-CALORIC-RESTRICTION. Nutrition for aging is owned by SBL-41/SP-NUTRITION-FOR-AGING.

Figures are original schematics. They are not measured dose–response curves and not fasting prescriptions. No third-party published figure has been reproduced.

29 Glossary

ADF. Alternate-day fasting; a zero- or near-zero-energy day alternated with a feast day.

eTRE. Early time-restricted eating; the daily eating window placed in the morning or early afternoon.

FMD. Fasting-mimicking diet; a periodic low-energy, low-protein formulated cycle, not a water-only fast.

Matched trial. A comparison in which energy (and, when stated, protein or weight loss) is equated across arms.

TRE. Time-restricted eating; food confined to a daily clock window, with or without a calorie target.