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Protein-forward14 human studies cited

Protein-Forward Fasting

16 hours without food · Daily

Written by Reviewed Sep 2026

Also called: High-protein time-restricted eating, Muscle-sparing fasting

A compressed eating window run deliberately at a high protein intake with resistance training. The central finding is that the lean-mass failure mode in this literature is low protein plus a compressed window plus time, not the window itself.

Overview

Every time-restricted eating trial that preserved lean mass ran protein at 1.6 to 2.2 g/kg/day alongside supervised resistance training. Tinsley 2019 at 1.6 g/kg/day, Stratton 2020 at 1.83 with an identical prescribed 25% deficit in both arms, Moro 2016 at 1.93 with calories and macronutrients matched, Blake 2025 at 2.2 in a 10% surplus. In all four, fat-free mass and strength outcomes were the same in the compressed-window arm as in the control arm.

The trial that lost more lean mass ran 1.0 g/kg/day. Parr 2023 put 18 men on an isoenergetic diet for 10 days, an 8-hour window against a 12-hour control, and measured integrated daily myofibrillar protein synthesis by deuterated water with repeated muscle sampling. Synthesis was identical between arms at 1.28 against 1.26 %/day (p = 0.82). Lean mass still fell further in the compressed arm, 1.0 kg against 0.2 kg (p = 0.01).

That is the one trial in the set that measured the mechanism and the outcome at the same time, and they disagreed. The window did not suppress protein synthesis. Something else took the lean mass, and the most obvious candidate is that the daily protein budget was roughly half what the trials that preserved lean mass were eating.

The honest limit on all of this: no trial has tested a compressed window at low protein with lean mass as a primary outcome over months. That is the largest gap in this literature for anyone who lifts.

How it works

The protocol is a normal compressed window with two things added deliberately. First, a protein target set high enough that the window is not the binding constraint: the preserving trials sat between 1.6 and 2.2 g/kg/day, and across 49 studies and 1863 participants in energy balance, protein supplementation produced no further fat-free mass gain above a total intake of about 1.62 g/kg/day. Second, resistance training, which is present in every trial in this literature where lean mass was maintained or gained during an energy deficit and absent from none of them.

Distribution across the window matters less than people expect. The acute tracer studies frequently find differences between even and skewed protein distribution; the chronic body composition trials mostly do not. The best-methodology null result used deuterated water plus dietary protein intrinsically labelled with a phenylalanine tracer in 24 adults aged 65 to 80 and found synthesis rates of 2.16 %/day even against 2.23 %/day skewed (p = 0.647). One synthesis of the field concludes that the effect of distribution cannot be disentangled from the effect of quantity, and that adults already eating 0.8 to 1.3 g/kg/day benefit from having at least one meal large enough to maximally stimulate synthesis rather than from a particular daily pattern.

Rate of loss is the third lever. Elite athletes losing at 0.7% of body weight per week gained 2.1% of lean body mass while those losing at 1.4% per week lost 0.2%, for the same total weight lost, although the slower group also accumulated more total training exposure.

What 16 hours actually reaches

Fasting does not switch muscle protein synthesis off. Postabsorptive myofibrillar fractional synthetic rate in healthy adults sits around 0.03 to 0.05 %/h and does not differ between young and older people. What feeding does is produce a rise on top of that, and what a compressed window changes is how many opportunities there are to produce it. At 72 hours of fasting, forearm net phenylalanine release rises and mTOR phosphorylation falls by about 50%, with reduced phosphorylation of 4EBP1, rpS6 and ULK1, while the MAFbx and MURF1 ubiquitin ligases are unchanged. Net muscle amino acid loss at that point is driven more by suppressed synthesis than by accelerated breakdown. A 16-hour daily window is nowhere near that state. The growth hormone claim deserves stating precisely, because it is usually stated wrongly. Growth hormone secretion rises roughly three to five fold within two to five days of fasting while IGF-1 falls. Suppressing growth hormone during a 40-hour fast raised urinary urea excretion by roughly 50% and increased muscle protein breakdown, so it is a genuine part of physiological protein conservation. But when lipolysis was blocked, adding growth hormone did not influence indexes of protein degradation at all, and the authors concluded that stimulation of lipolysis is its principal protein-conserving mechanism. It spares protein by liberating fatty acids so the body burns fat instead of amino acids, not by acting as an anabolic on muscle. In fully adapted prolonged starvation it failed outright: urea excretion fell 50% while urinary ammonia rose 50% and total nitrogen loss was unchanged.

Fig. 1 · what has been measured, hour by hour
  1. 0h to 4h

    Still absorbing

    Burning
    Glucose from the meal just eaten, with insulin high enough to hold fat release down
    • Insulin is at its post-meal peak, and while it is there, adipose tissue lipase stays suppressed and fat is being stored rather than released.
    • The hour count on most fasting charts starts at the last bite. Absorption of a mixed meal is still running here, so the clock and the physiology are not yet the same thing.

    Read the biologyInsulin and insulin sensitivity during a fast

    Measured in people
    The human hour-by-hour fasting series begin later than this. Klein 1993 took its first sample at 12 hours in 6 healthy men, and Rothman 1991 reports its first gluconeogenesis figure as an average across the first 22 hours. This row is the fed state those measurements are compared against, and no extended-fasting measurement exists inside it.

  2. 4h to 12h

    Post-absorptive

    Burning
    A mix of remaining glucose and fatty acids, with the liver covering the brain's glucose demand
    Blood glucose
    5.58 ± 0.08 mmol/L (100.5 mg/dL) at the 12 hour mark, in 6 healthy men
    Ketones (BHB)
    Total ketone bodies around 0.20 mmol/L in overnight-fasted subjects. That figure is acetoacetate plus beta-hydroxybutyrate, not BHB on its own.
    Insulin
    64.6 ± 12.9 pmol/L (9.3 microunits/mL) at 12 hours, in the same 6 men
    • Glycerol release runs at 2.08 ± 0.22 and palmitic acid release at 1.63 ± 0.20 micromol/kg/min at 12 hours. Those are the numbers everything later in the fast is measured against.
    • Gluconeogenesis is already the majority contributor to glucose production rather than a reserve waiting to be called on, which is the first place the popular switch model breaks.

    Read the biologyInsulin and insulin sensitivity during a fastGlycogen depletion and gluconeogenesis

    Measured in people
    Klein 1993 measured glucose, insulin and stable-isotope lipid kinetics at 12 hours in 6 healthy men. Féry 1983 measured total ketone body turnover in overnight-fasted subjects and put the baseline at 0.20 mmol/L. Rothman 1991 measured hepatic glycogen serially by 13C nuclear magnetic resonance through a 68 hour fast in healthy adults and calculated that gluconeogenesis supplied 64 ± 5% of total glucose production across the first 22 hours.

  3. 12h to 18h

    Ketones have not moved yet

    Burning
    Fatty acids rising, with glucose production increasingly made rather than released from store
    Ketones (BHB)
    Median change of 0% between 12 and 18 hours, sampled every 6 hours in 34 adults
    • Beta-hydroxybutyrate does not move in this window. In 34 adults sampled every 6 hours through the standard diagnostic 72 hour fast, the median change from 12 to 18 hours was zero.
    • Gluconeogenesis is supplying 64 ± 5% of glucose production across the first 22 hours, confirmed by an orthogonal method at about 47% by 14 hours. Glucose production does not switch from glycogen to fat at a threshold hour.
    • Whole blood LC3A messenger RNA was 22 ± 5% higher at 18 hours than in a 12 hour control arm in 11 overweight adults (p = 0.001). In the same subjects MTOR expression also rose, by 9 ± 3%.

    Read the biologyGlycogen depletion and gluconeogenesisKetogenesis and beta-hydroxybutyrateAutophagy

    Measured in people
    Service 2005 measured beta-hydroxybutyrate every 6 hours in 34 adults whose 72 hour fasts were negative for insulinoma. Rothman 1991 measured the gluconeogenic share by 13C NMR. Jamshed 2019 measured whole blood messenger RNA in an 11-person 4 day randomised crossover of an 08:00 to 14:00 eating window against 08:00 to 20:00. That is one gene's expression in blood cells, not autophagic flux and not muscle. No study in any species has tested a 16 hour timepoint for autophagy.

  4. 18h to 1d

    The steepest hours for fat release

    past this window
    Burning
    Fatty acids and glycerol, with ketone production starting its climb
    Ketones (BHB)
    Climbing. The median rise from 18 to 36 hours was +333%, the steepest proportional stretch of a 72 hour fast.
    Insulin
    70% of the entire decline seen across a 72 hour fast has already happened by 24 hours
    • The largest single interval increase in lipolysis across a whole 72 hour fast falls between 18 and 24 hours, and 60% of the total rise in lipid kinetics happens between 12 and 24 hours. The authors attribute that to the falling insulin rather than to any change in glucose.
    • Growth hormone was significantly higher after a 24 hour water-only fast than after a fed day in a randomised crossover of 30 healthy adults (p = 1.1 x 10^-4). The size of that rise is not in the accessible record and is not published here.
    • Haemoglobin, red cell count and haematocrit all rose together at 24 hours in the same trial. That combination is the signature of plasma volume contraction, not of new red cells.
    • 24 hour energy expenditure measured in a whole-room calorimeter fell during 24 hour fasting in 20 volunteers, with the size of the fall varying between individuals.

    Read the biologyInsulin and insulin sensitivity during a fastThe growth hormone responseKetogenesis and beta-hydroxybutyrateAutophagy

    Measured in people
    Horne 2013 randomised 30 apparently healthy adults to a 24 hour water-only fast or a day of usual eating in crossover and measured growth hormone, blood counts, cholesterol, triglycerides, bicarbonate and weight. Klein 1993 measured the lipid kinetics by stable isotope tracer. Hollstein 2020 measured 24 hour energy expenditure by whole-room calorimetry in 20 volunteers; the exact percentage decrease is not in the accessible record and is not published here. On autophagy, a 24 hour fast raised p62/SQSTM1 in the vastus lateralis of 50 women, which is movement in the direction of less autophagic degradation rather than more.

  5. 1d to 36h

    Thyroid drops before metabolic rate does

    past this window
    Burning
    Fat, with the remaining glucose built from glycerol, lactate and amino acids
    Ketones (BHB)
    1.308 ± 1.053 mmol/L after day 1 in 13 men beginning a 10 day water fast, from a baseline of 0.177 ± 0.044. The spread on that mean is as wide as the mean.
    • Gluconeogenesis supplies 82 ± 5% of glucose production between 22 and 36 hours.
    • Serum T3 fell from 2.30 ± 0.06 to 1.84 ± 0.03 nmol/L by 30 hours in 8 healthy men (p < 0.01), TSH fell below 1 mU/L and the nocturnal TSH peak was abolished. Serum cortisol did not differ across conditions.
    • Thyroid suppression therefore begins inside the first 30 hours, well before any measurable fall in resting metabolic rate.
    • Sodium excretion has not turned yet. In 9 obese women fasting with pre-fast salt intake maintained, urinary sodium began to rise after roughly 48 hours and then exceeded intake.

    Read the biologyGlycogen depletion and gluconeogenesisKetogenesis and beta-hydroxybutyrateAutophagy

    Measured in people
    Rothman 1991 measured the gluconeogenic share by 13C NMR in healthy adults. Hugues 1984 fasted 8 healthy men for 30 hours with serial thyroid sampling. Dai 2022 measured blood beta-hydroxybutyrate daily in 13 men fasting in a controlled facility. Sigler 1975 collected urine in 3 hour blocks from 9 obese women on a metabolic ward. On autophagy, the only human study with several within-fast timepoints took vastus lateralis biopsies at 2, 12, 24 and 36 hours: LC3I, LC3II and p62 all fell, in untrained subjects only, which the authors summarise as skeletal muscle autophagy being only modestly affected by 36 hours of fasting.

Human evidence

Four randomised trials of compressed windows at 1.6 to 2.2 g/kg/day with supervised resistance training, one trial at 1.0 g/kg/day that measured protein synthesis and body composition together, and the protein dose-response trials that establish what the targets mean.

  • Parr 2023, 18 men, mean age 46, BMI 30, isoenergetic diet at about 1.0 g/kg/day protein, 10 days of a 10:00 to 18:00 window versus 08:00 to 20:00. Integrated daily myofibrillar protein synthesis by deuterated water did not differ (1.28 versus 1.26 %/day, p = 0.82). 24-hour glucose area under the curve fell in the compressed arm (p = 0.001). Total body mass declined similarly (-1.6 versus -1.1 kg, p = 0.22) but lean mass loss was greater in the compressed arm (-1.0 versus -0.2 kg, p = 0.01) (Obesity, 2023).
  • Tinsley 2019, 40 resistance-trained women randomised, 8 weeks of supervised training three days a week, achieved windows of about 7.5 hours against 13.2 hours in control, protein 1.6 g/kg/day in all three groups (p = 0.58), body composition by a modified four-compartment model plus ultrasound. Fat-free mass rose 2% to 3% in all groups with no between-group difference, muscle thickness rose in all groups, and performance improved in all groups. The fat mass difference was significant in the per-protocol analysis and not in the intention-to-treat analysis (American Journal of Clinical Nutrition, 2019).
  • Stratton 2020, 26 analysed, 4 weeks, supervised training, both arms prescribed an identical 25% energy deficit and identical 1.8 g/kg/day protein and achieving it (1.83 versus 1.83 g/kg/day, p = 0.956; energy p = 0.950), body composition by a four-compartment model plus ultrasound. Significant time effects and no group by time interaction on any body composition or strength variable. Fat-free mass was maintained equally. Cortisol rose significantly only in the normal diet group (Nutrients, 2020).
  • Moro 2016, 34 resistance-trained men, 8 weeks, energy and macronutrients matched, protein 1.93 versus 1.89 g/kg/day, supervised training inside the feeding window. Fat mass fell in the compressed arm (interaction P = 0.0448); fat-free mass, limb area and maximal strength were maintained in both. Testosterone and IGF-1 fell in the compressed arm only. Followed to 12 months in 20 participants, the same cohort showed arm muscle cross-sectional area down 4.31% and thigh down 2.90% while the control arm gained, alongside a spontaneous 6.4% fall in energy intake, with strength rising equally in both arms (Journal of Translational Medicine, 2016; Medicine and Science in Sports and Exercise, 2021).
  • Blake 2025, 17 well-trained men and women, 8 weeks of supervised progressively overloaded training four days a week, both arms in a 10% caloric surplus at 2.2 g/kg/day. Fat-free mass rose in both, 2.67 kg in the compressed arm against 1.82 kg (p = 0.04), and the control arm added 1.4 kg more fat mass (p = 0.04). Squat one-rep max gains were 4.0 kg lower in the compressed arm (p = 0.05), which tracks a training volume deficit of 6960 against 7334 total repetitions. This is the only trial in the set where the compressed arm trained fasted (Journal of the International Society of Sports Nutrition, 2025).
  • Longland 2016, 40 young men, 4 weeks at roughly 40% below energy requirements with resistance plus interval training six days a week, 1.2 against 2.4 g/kg/day, four-compartment model. Lean body mass rose 1.2 kg on higher protein against 0.1 kg on lower (p < 0.05) and fat mass fell 4.8 kg against 3.5 kg (p < 0.05). Lean mass increased during a 40% deficit rather than merely being spared (American Journal of Clinical Nutrition, 2016).
  • Mettler 2010, 20 resistance-trained athletes, 2 weeks at 60% of habitual energy intake at roughly 1.0 against 2.3 g/kg/day. Lean body mass loss was 1.6 kg on the lower intake and 0.3 kg on the higher (p = 0.006), with fat loss and performance not differing. The abstract also reports that fatigue ratings were higher in the high-protein group (Medicine and Science in Sports and Exercise, 2010).

What this does not tell you: Sample sizes across the compressed-window training trials run from 17 to 26 analysed, with 20 in the only 12-month trial. Every one is underpowered to detect a between-group lean mass difference, so the null results are weak evidence of no effect rather than proof of equivalence. Trial durations run 4 weeks to 12 months, and only one reached 12 months. Two of the trials measured limb muscle area by anthropometry rather than imaging. No trial has run a compressed window at 1.0 against 1.8 g/kg/day with lean mass as a primary outcome for six months or longer.

Reading the research record

The conflicts in this literature are real and they resolve differently depending on which variable you hold constant.

On fat loss, Moro 2016 found the compressed window beating a matched diet (interaction p = 0.0448) while Stratton 2020, which prescribed and verified an identical deficit and identical protein, found the difference gone. Moro's arms ate habitually and the compressed arm ended up eating about 175 kcal/day less. A meta-analysis of time-restricted eating plus resistance training found energy intake reduced by 174.88 kcal/day, essentially the same number. The reading that fits all of those at once is that time restriction acts as a covert calorie-restriction tool, which is an interpretation rather than a finding.

On lean mass the trials genuinely split, and the candidate explanations are ordered rather than settled. Duration: every null trial ran 4 to 8 weeks and the only 12-month trial found limb muscle area falling. Protein intake: the preserving trials ran 1.6 to 2.2 g/kg/day and the trial that lost more lean mass ran 1.0. Energy balance direction: in a 10% surplus the compressed window did not harm lean mass at all and gained more of it than the control arm. Measurement method: the trials using four-compartment models and ultrasound found no group differences, while the two trials that found losses used anthropometry-derived limb area, although the direction of the 12-month result is hard to explain as a skinfold artefact, since the arm that lost fat is the arm whose measured area went down. Statistical framework: the same 2019 dataset yields a null or a compressed-window advantage on fat mass depending on intention-to-treat against per-protocol analysis.

One widely repeated protein-forward result needs correcting rather than repeating. The intermittent fasting and protein pacing trial reported greater weight and visceral fat loss than calorie restriction, and it is frequently summarised as showing that protein pacing preserves muscle. The paper's own numbers say both arms lost about 1.5 kg of fat-free mass. What rose was the proportion of fat-free mass to total body weight, 5.7% against 3.0% (p = 0.030), because the protein pacing arm lost more fat. That is a percentage effect, not preservation of absolute lean mass. The trial was sponsored by Isagenix International, whose products were the study foods in the protein pacing arm while the comparator arm ate unbranded home-cooked food, employees of the sponsor are co-authors, the two arms differed in protein, food form and fibre at once, and as of this review there is no independent replication by another group.

What happens to muscle

This is the field this protocol exists to address, and the numbers are specific.

At 1.6 to 2.2 g/kg/day with supervised resistance training, four randomised trials found fat-free mass and strength outcomes indistinguishable between a compressed window and normal eating, over 4 to 8 weeks, using four-compartment models and ultrasound in two of them. In a 10% surplus at 2.2 g/kg/day the compressed arm gained more fat-free mass than the control arm, 2.67 against 1.82 kg (p = 0.04).

At 1.0 g/kg/day over 10 days, lean mass fell 1.0 kg against 0.2 kg in the 12-hour control (p = 0.01) while integrated daily myofibrillar protein synthesis was 1.28 against 1.26 %/day (p = 0.82). Mechanism unchanged, outcome different.

Across an energy deficit generally, the proportion of weight lost as fat-free mass was lower and fat loss higher at 1.6 and 2.4 g/kg/day than at 0.8, and the anabolic response to a protein-rich meal was preserved at the two higher intakes and blunted at the RDA. Note that 1.6 and 2.4 performed the same in that trial: the benefit came from clearing the RDA, not from maximising. In athletes at 60% of habitual intake, lean mass loss was 1.6 kg at roughly 1.0 g/kg/day and 0.3 kg at roughly 2.3.

How much lean mass anyone loses also depends on how much fat they started with. Total body nitrogen loss per kilogram of weight lost is inversely related to body fat, roughly 20 g of nitrogen per kg in the non-obese against roughly 10 g per kg in people carrying 50 kg or more of fat. Converted at 6.25 g of protein per gram of nitrogen and lean tissue as roughly 20% protein, that corresponds to about 60% of weight loss coming from lean tissue in a lean person and roughly 30% in the very obese. Those conversions are standard stoichiometry rather than measurements, and they are the reason a lean lifter and a person with obesity should not be given the same fasting parameters.

One measurement caution that changes how scans should be read: the lean soft tissue compartment on a DXA is largely water, and glycogen binds roughly three times its own weight in water. In a 10-day fasting study, 58% of the measured lean soft tissue loss was water and glycogen rather than tissue. A scan taken at the end of a fast overstates lean loss and one taken after refeeding overstates lean regain.

Doing it

Protein target
1.6 to 2.2 g/kg/day is the range every preserving trial ran. Above a total of about 1.62 g/kg/day, protein supplementation produced no further fat-free mass gain across 49 studies and 1863 participants in energy balance. In a deep deficit with hard training, 2.4 g/kg/day produced a 1.2 kg lean mass gain where 1.2 g/kg/day produced 0.1 kg.
Denominator matters
The original protein sparing modified fast prescriptions were written in grams per kilogram of ideal body weight, not lean body mass. In the randomised test of the dose, 1.5 g/kg of ideal body weight held nitrogen balance at zero on a 500 kcal diet while 0.8 g/kg gave -2 g of nitrogen per day. The grams per kilogram of lean body mass framing is a later clinical convention.
Train against resistance, and consider training fed
Resistance training is present in every trial where lean mass was maintained or gained during a deficit. The one trial where the compressed arm trained fasted completed 374 fewer total repetitions and gained 4.0 kg less on the squat one-rep max (p = 0.05) with calories and protein matched, and it is rarely stated that in most other trials the compressed arm trained inside its feeding window.
Distribution is a lever for people who are under-eating protein
Acute tracer studies often find distribution effects; chronic body composition trials mostly do not. The best-methodology null used deuterated water plus intrinsically labelled dietary protein in 24 older adults and found 2.16 against 2.23 %/day (p = 0.647). For people already hitting their total, the evidence supports having at least one meal large enough to maximally stimulate synthesis.
Slow the rate of loss
For the same total weight lost, elite athletes losing 0.7% of body weight per week gained 2.1% of lean body mass while those losing 1.4% per week lost 0.2% (between-group p < 0.01). The slower group also accumulated more training exposure, which is a confound the authors name.
Age narrows the margin
Postprandial muscle protein synthesis is about 16% lower in older men, and after exercise 40 g beat 20 g in men around 71 where 20 g was sufficient in young men. A retrospective pooled reanalysis put the per-meal plateau at 0.40 g/kg body mass in older men against 0.24 in younger men, a comparison that did not reach significance (p = 0.055) and cleared it only per kilogram of lean body mass (p < 0.01). No compressed-window trial has been run in older adults with lean mass as the primary outcome.

Breaking the fast

The strongest single measurement behind the protein-forward model comes from refeeding after a prolonged fast rather than from a daily window. In 10 moderately obese women after a three-week fast, one week of 80 g of protein a day moved nitrogen balance from -5.9 g/day to +1.7 g/day (P < 0.05), while 80 g of carbohydrate moved it only to -3.1 g/day. The same shape appeared in the protein sparing modified fast work, where net protein anabolism was achieved on a protein-only, energy-deficient refeed after a lean mass deficit had been created. For a daily window, what applies is dose rather than order. A 100 g protein dose after whole-body resistance exercise produced a greater and longer anabolic response than 25 g, lasting beyond 12 hours, with negligible change in amino acid oxidation, so a large first meal is not wasted. Someone eating 150 g of protein across three meals inside an 8-hour window is not, on the human evidence, throwing the surplus away.

Citations

  1. Human2023
    Eight-hour time-restricted eating does not lower daily myofibrillar protein synthesis rates: A randomized control trial

    Obesity (Silver Spring)

    18 healthy males, mean age 46, BMI 30, isoenergetic diet at about 1.0 g/kg/day protein, 10 days of a 10:00 to 18:00 window versus 08:00 to 20:00, integrated myofibrillar synthesis by deuterated water with repeated muscle sampling. Synthesis did not differ (1.28 versus 1.26 %/day, p = 0.82). 24-hour glucose area under the curve fell (p = 0.001). Total mass fell similarly (-1.6 versus -1.1 kg, p = 0.22) but lean mass loss was greater in the compressed arm (-1.0 versus -0.2 kg, p = 0.01).

  2. Human2019
    Time-restricted feeding plus resistance training in active females: a randomized trial

    American Journal of Clinical Nutrition

    40 resistance-trained women randomised, 8 weeks of supervised training, achieved windows 7.5 and 7.6 hours against 13.2 in control, protein 1.6 g/kg/day in all groups (p = 0.58), body composition by a modified four-compartment model plus ultrasound. Fat-free mass rose 2% to 3% in all groups with no between-group difference; muscle thickness and performance improved in all groups. The fat mass difference was significant per protocol and not in the intention-to-treat analysis.

  3. Human2020
    Four Weeks of Time-Restricted Feeding Combined with Resistance Training Does Not Differentially Influence Measures of Body Composition, Muscle Performance, Resting Energy Expenditure, and Blood Biomarkers

    Nutrients

    26 analysed, 4 weeks, supervised training three times a week, both arms prescribed an identical 25% deficit and 1.8 g/kg/day protein and achieving it (1.83 versus 1.83 g/kg/day, p = 0.956; energy 1946 versus 1939 kcal/day, p = 0.950). Body composition by a four-compartment model plus ultrasound. Significant time effects and no group by time interaction on any body composition or strength variable; fat-free mass maintained equally. Cortisol rose significantly only in the normal diet group.

  4. Human2016
    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

    34 resistance-trained men, 8 weeks, energy and macronutrients matched, protein 1.93 versus 1.89 g/kg/day, supervised training performed inside the feeding window. Fat mass fell in the compressed arm (interaction P = 0.0448) with fat-free mass, limb area and maximal strength maintained in both. Testosterone fell from 21.26 to 16.86 nmol/L and IGF-1 from 216.94 to 188.90 ng/mL in the compressed arm only.

  5. Human2021
    Twelve Months of Time-restricted Eating and Resistance Training Improves Inflammatory Markers and Cardiometabolic Risk Factors

    Medicine and Science in Sports and Exercise

    The same cohort at 12 months, 20 analysed, protein matched throughout at 1.79 to 1.93 g/kg/day in both arms. Arm muscle cross-sectional area -4.31% (p = 0.003) and thigh -2.90% (p = 0.03) in the compressed arm while the control arm gained 11.87% and 6.94%; fat-free mass interaction p = 0.002. Energy intake in the compressed arm fell 6.4% spontaneously (p < 0.0001). Strength rose equally in both arms. The widely quoted 18.8% visceral fat reduction was not significant (p = 0.518). Limb area by anthropometry, not imaging.

  6. Human2025
    Hypercaloric 16:8 time-restricted eating during 8 weeks of resistance exercise in well-trained men and women

    Journal of the International Society of Sports Nutrition

    17 well-trained participants, 8 weeks of supervised progressively overloaded training four days a week, both arms in a 10% caloric surplus at 2.2 g/kg/day protein, body composition by a three-compartment model. Fat-free mass rose 2.67 kg in the compressed arm against 1.82 kg (p = 0.04) and the fed arm added 1.4 kg more fat mass (p = 0.04). Squat one-rep max gains were 4.0 kg lower in the compressed arm (p = 0.05), alongside significantly lower total training volume (6960 versus 7334 repetitions). The only trial in the set where the compressed arm trained fasted.

  7. Human2016
    Higher compared with lower dietary protein during an energy deficit combined with intense exercise promotes greater lean mass gain and fat mass loss: a randomized trial

    American Journal of Clinical Nutrition

    40 young men, 20 per group, 4 weeks at roughly 40% below energy requirements with resistance plus high-intensity interval training six days a week, 1.2 versus 2.4 g/kg/day, four-compartment model. Lean body mass +1.2 kg on higher protein versus +0.1 kg (p < 0.05); fat mass -4.8 versus -3.5 kg (p < 0.05). Exercise performance improved similarly in both. Lean mass increased during a 40% deficit rather than merely being spared.

  8. Human2010
    Increased protein intake reduces lean body mass loss during weight loss in athletes

    Medicine and Science in Sports and Exercise

    20 resistance-trained athletes, 2 weeks at 60% of habitual energy intake, 15% of energy as protein (about 1.0 g/kg) versus 35% (about 2.3 g/kg). Total mass loss -3.0 versus -1.5 kg (p = 0.036); lean body mass loss -1.6 versus -0.3 kg (p = 0.006). Fat loss and performance did not differ. The abstract reports fatigue ratings and worse-than-normal scores were higher in the high-protein group.

  9. Human2023
    The anabolic response to protein ingestion during recovery from exercise has no upper limit in magnitude and duration in vivo in humans

    Cell Reports Medicine

    36 recreationally active young men, 12 per group, 0 g, 25 g or 100 g of intrinsically labelled milk protein after 60 minutes of whole-body resistance exercise. 100 g produced a greater and more prolonged response than 25 g, lasting beyond 12 hours, with myofibrillar synthesis roughly 20% higher over 0 to 4 hours and roughly 40% higher over 4 to 12 hours, and negligible effect on whole-body protein breakdown or amino acid oxidation.

  10. Human1984
    Metabolic effects of very low calorie weight reduction diets

    Journal of Clinical Investigation

    17 healthy obese women randomised for 5 or 8 weeks to two isocaloric 500 kcal diets, one providing 1.5 g protein per kg of ideal body weight and the other 0.8 g/kg plus 0.7 g carbohydrate/kg, with leucine and alanine tracer infusions. After 3 weeks of adaptation, nitrogen balance was zero on the 1.5 g/kg diet and -2 g of nitrogen per day on the 0.8 g/kg diet. Note the denominator: ideal body weight, not lean body mass.

  11. Human1976
    Nitrogen metabolism and insulin requirements in obese diabetic adults on a protein-sparing modified fast

    Diabetes

    The origin of the protein sparing modified fast prescription, in 7 obese adults with adult-onset diabetes taking 30 to 100 units of insulin per day. Protein was given at 1.2 to 1.4 g per kg of ideal body weight, with nitrogen balance maintained chronically at 1.3 g/kg of ideal body weight in the 3 patients who had extensive balance studies. Insulin was discontinued in all 7 patients after 0 to 19 days, mean 6.5 days.

  12. Human1990
    Protein metabolic effects of a prolonged fast and hypocaloric refeeding

    American Journal of Physiology

    10 moderately obese women, a 3-week fast followed by random allocation to one week of refeeding with 80 g of carbohydrate or 80 g of protein. After the fast, plasma leucine flux and urinary 3-methylhistidine excretion had both fallen 31% and nitrogen balance was -5.9 g/day. Protein refeeding made nitrogen balance positive at +1.7 g/day (P < 0.05); carbohydrate refeeding improved it only to -3.1 g/day while leucine flux fell a further 18%.

  13. Human2011
    Effect of two different weight-loss rates on body composition and strength and power-related performance in elite athletes

    International Journal of Sport Nutrition and Exercise Metabolism

    24 elite athletes randomised to a slow reduction targeting 0.7% of body weight per week (n = 13) or a fast reduction targeting 1.4% (n = 11), with four resistance sessions a week in both and DXA. Body weight fell 5.6% and 5.5%, matched. Fat mass -31% versus -21%. Lean body mass +2.1% in the slow group (p < 0.001) versus -0.2% in the fast group (between-group p < 0.01). The slow group also accumulated more total training exposure, which the authors name as a confound.

  14. Human2023
    Intermittent fasting and protein pacing are superior to caloric restriction for weight and visceral fat loss

    Obesity (Silver Spring)

    41 randomised, 39 analysed, 8 weeks. The protein pacing arm lost more weight (-8.2 versus -5.0 kg, p = 0.009) and visceral fat (-33% versus -15.8%, p = 0.030). On lean mass the paper's own words are that absolute fat-free mass decreased in both groups by about 1.5 kg; what rose was the proportion of fat-free mass to body weight (5.7% versus 3.0%, p = 0.030). Sponsored by Isagenix International, whose products were the study foods in the protein pacing arm while the comparator ate unbranded home-cooked food, with sponsor employees as co-authors. No independent replication was identified.

What people report

These are uncontrolled self-reports, not evidence. They are here because they tell you what to expect and what to watch for, which the trial literature does not. They cannot tell you whether anything works.

  • Reaching the protein target inside the window being the practical constraint, not hunger
  • Training inside the feeding window rather than before it
  • Larger single protein feedings than usual, which the dose-response evidence supports
  • Fatigue at very high protein intakes during a deficit, which was also reported inside a trial
  • Lower subjective daily energy when training fasted, reported alongside a measured training volume deficit

Sources: Uncontrolled self-report, except for the fatigue item, which was reported in the abstract of the two-week athlete trial as higher in the high-protein group, and the subjective energy item, which was reported alongside a measured 374-repetition training volume deficit in the fasted-training trial. A separate review of what fasting communities report is still being compiled and nothing here is drawn from it.

Who this is wrong for

  • Anyone who cannot reliably reach 1.6 g/kg/day of protein inside their window. That is precisely the condition the 1.0 g/kg/day trial measured, and lean mass fell further while protein synthesis was unchanged.
  • Anyone taking an SGLT2 inhibitor without a prescriber stopping it first.
  • Anyone on insulin, a sulfonylurea or a meglitinide without a prescriber adjusting the dose against a compressed intake window.
  • Pregnancy and breastfeeding.
  • Anyone with a history of an eating disorder or current loss-of-control eating. Stacking a protein target on top of a window rule adds a second thing to be scored by.
  • Children and adolescents.
  • Anyone with a BMI under 18.5 or meeting the NICE refeeding risk criteria.
  • Anyone with severe kidney disease, which is the exception both major geriatric protein guidelines name when recommending 1.0 to 1.2 g/kg/day for people over 65 and at least 1.2 g/kg/day for those exercising.
  • Older adults over 65 who want to run this on the published trial evidence, because there is none. No compressed-window trial has been run in that group with lean mass as the primary outcome, and the per-meal dose findings suggest the margin is narrower there.
  • Anyone already lean and deeply restricted, where one systematic review of energy-restricted resistance-trained athletes puts protein needs at 2.3 to 3.1 g/kg of fat-free mass, which becomes hard to fit inside a short window.

Questions

Does a compressed eating window cost muscle?
Not at adequate protein, in trials of 4 to 8 weeks. Four randomised trials at 1.6 to 2.2 g/kg/day with supervised resistance training found fat-free mass and strength outcomes the same as normal eating, and in a 10% surplus the compressed arm gained more. The trial that ran 1.0 g/kg/day lost 1.0 kg of lean mass against 0.2 kg in its 12-hour control while integrated daily myofibrillar protein synthesis was identical. The failure mode is low protein plus a compressed window plus time.
How much protein, exactly?
1.6 to 2.2 g/kg/day is the range that preserved lean mass in every compressed-window trial. Above about 1.62 g/kg/day, supplementation added no further fat-free mass across 49 studies in energy balance. In a 40% deficit with hard training, 2.4 g/kg/day produced a 1.2 kg lean mass gain where 1.2 g/kg/day produced 0.1 kg, and in a separate trial 1.6 and 2.4 g/kg/day performed identically, so the benefit came from clearing the RDA rather than from maximising.
Does it matter how the protein is spread across the window?
Less than the acute studies suggest. Tracer studies frequently find distribution effects on synthesis rates; the chronic body composition trials mostly do not. The strongest null used deuterated water plus intrinsically labelled dietary protein in 24 adults aged 65 to 80 and found 2.16 against 2.23 %/day (p = 0.647). One synthesis of the field concludes that distribution cannot be disentangled from quantity, and that adults already hitting their total benefit from having at least one meal large enough to maximally stimulate synthesis.
Does the fasting growth hormone rise protect muscle?
It contributes, and not the way the claim implies. Growth hormone secretion rises three to five fold within two to five days of fasting while IGF-1 falls, and suppressing it during a 40-hour fast raised urea-nitrogen excretion by roughly 50%. But when lipolysis was blocked, adding growth hormone did not influence protein degradation at all, and the authors concluded that stimulating lipolysis is its principal protein-conserving mechanism. In fully adapted prolonged starvation it did not reduce total nitrogen loss: urea fell 50% while ammonia rose 50%.
What has not been tested?
A trial of a compressed window at 1.0 against 1.8 g/kg/day, matched for calories, with resistance training and a four-compartment or imaging endpoint, running at least six months. Nothing like it exists. Every trial in this section analysed between 17 and 26 people, so the null results are weak evidence of no effect rather than evidence of equivalence.