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Time-restricted7 human studies cited

Early Time-Restricted Eating

18 hours without food · Daily

Written by Reviewed Sep 2026

Also called: eTRF, Early time-restricted feeding, Front-loaded eating

The eating window moved to the front of the day, finishing mid-afternoon. It is the only fasting pattern with a controlled-feeding trial showing metabolic improvement while weight was deliberately held constant, and that trial had eight completers.

Overview

Early time-restricted eating puts the window early: 07:00 to 15:00 in Jamshed 2022, 08:00 to 14:00 in the crossover that measured autophagy gene expression, and a six-hour window with dinner finished before 15:00 in Sutton 2018. The logic behind it is circadian, that insulin sensitivity and the thermic effect of food are higher in the morning, but the reason it matters on this page is narrower than that.

It is the only pattern where a trial provided every meal, matched them meal by meal against the control arm, and fed participants enough to hold their weight stable. Insulin sensitivity, beta cell responsiveness and blood pressure still improved. That design answers a question no free-living trial can answer, and it answered it in eight men with prediabetes.

Everything else in this section is free-living and produces the usual mixture of weight change and self-reported diet.

How it works

Move the window forward rather than shortening it further. In practice that means breakfast, lunch, an early dinner, and nothing after mid-afternoon.

Jamshed's participants adhered 6.0 days per week over 14 weeks, which is close to the adherence reported for later windows in the same literature, so the early placement did not obviously cost compliance in that trial. Sutton's supervised participants adhered 100% to provided meals, which tells you about the design rather than about the protocol.

The secondary per-protocol analysis of Jamshed's trial found something that should be stated alongside the benefits: the participants who adhered most consistently self-reported sleeping less and taking longer to fall asleep, while also reporting less fatigue. The authors state directly that it is not yet known whether shortening sleep while reducing fatigue is healthful.

What 18 hours actually reaches

What was measured under controlled feeding, with no weight change, is a 36 U/mg fall in insulin resistance by the 3-hour incremental AUC ratio (P = 0.005), a 14 U/mg rise in the insulinogenic index (P = 0.05), an 11 mmHg fall in morning systolic and 10 mmHg in diastolic blood pressure (both P = 0.03), and an 11 pg/mL fall in plasma 8-isoprostane (P = 0.05). Glucose did not improve over five weeks, and the authors say so plainly. The oxidative stress result was driven partly by a worsening in the control arm, so the honest reading is that the early window prevented a rise rather than produced a fall. This is also the window placement where the direct human autophagy measurement sits. Four days of an 08:00 to 14:00 window raised whole blood cell expression of LC3A and SIRT1 before breakfast (p < 0.04) and MTOR in the evening (p = 0.007) in 11 overweight adults, alongside a 4 mg/dL drop in mean 24-hour glucose. Gene expression in blood cells is a marker, not a flux measurement, and it is not muscle or liver, which is where fasting-induced autophagy is clearest in animals and where nobody biopsies a healthy volunteer. No human trial has measured mitophagy in response to any fasting protocol, at this window or any other.

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

One supervised isocaloric controlled-feeding crossover, one 14-week randomised trial with energy restriction matched across arms, one per-protocol secondary analysis of that trial, and two crossover trials comparing early against later windows.

  • Sutton 2018, 5-week randomised crossover, isocaloric and eucaloric controlled feeding with meals provided and matched meal by meal, eaten in clinic or under real-time remote video supervision. 12 men with prediabetes enrolled to obtain the 8 completers the power calculation required. Insulin resistance fell 36 U/mg (P = 0.005), the insulinogenic index rose 14 U/mg (P = 0.05), morning blood pressure fell 11 over 10 mmHg (both P = 0.03) and 8-isoprostane fell about 14% relative to control. Arterial stiffness, LDL and HDL did not improve; resting heart rate, triglycerides and total cholesterol increased or tended to increase in the morning measurements (Cell Metabolism, 2018).
  • Jamshed 2022, 14 weeks, 90 adults with a mean BMI of 39.6 at a university weight loss clinic, all receiving energy restriction and weight-loss treatment. A 07:00 to 15:00 window produced 2.3 kg more weight loss than a 12-hour-or-longer window with the same energy restriction (95% CI -3.7 to -0.9; P = .002) and 4 mmHg better diastolic blood pressure (P = .04), with improvements in fatigue, vigour and depression scores. Fat loss did not differ (-1.4 kg; P = .09) and neither did the ratio of fat loss to weight loss (P = .43). The authors put the size of the effect as equivalent to cutting about 214 kcal/d (JAMA Internal Medicine, 2022).
  • Steger 2023, the per-protocol analysis of the same 90 participants restricted to those adhering at least 5 days a week every week. Against adherers in the control arm: weight -3.7 kg (P = 0.003), body fat -2.8 kg (P = 0.04), heart rate -7 beats/min (P = 0.02), insulin resistance -2.80 (P = 0.047), glucose -9 mg/dL (P = 0.047). The same analysis found consistent adherers reporting less sleep and longer sleep onset. This answers what happens in people who stick to it, not what happens when it is prescribed (Obesity, 2023).
  • Hutchison 2019, randomised crossover in 15 men at risk of type 2 diabetes, 7 days each of an early 08:00 to 17:00 window and a delayed 12:00 to 21:00 window with continuous glucose monitoring. Glucose tolerance improved and fasting triglycerides fell in both conditions versus baseline. Mean fasting glucose was lower in the early condition (P = 0.02) and not the delayed (P = 0.17), but the two conditions did not differ from each other, so this trial does not establish early over late (Obesity, 2019).
  • Xie 2022, 5 weeks in 90 randomised and 82 analysed healthy adults without obesity. Early time-restricted eating improved insulin sensitivity more than a mid-day window, and only the early arm improved fasting glucose, reduced total body mass and adiposity, reduced inflammation and increased gut microbial diversity. Outcome assessors were blinded; participants were not (Nature Communications, 2022).

What this does not tell you: The controlled-feeding trial has 8 completers and a documented carryover effect: after a 7-week washout, all but one participant who did the early arm first entered the second arm with mean postprandial insulin at least 25% below baseline. Jamshed's lean mass change as a discrete number is not in the abstract record and could not be verified, so this page does not publish one for that trial. Hutchison ran 7 days per condition in 15 men. Xie ran 5 weeks in healthy people without obesity.

Reading the research record

Two questions are open here and the trials genuinely split on both.

The first is whether an early window beats a later one. Xie 2022 found early better than mid-day for insulin sensitivity in 82 analysed participants. Hutchison 2019 found the early and delayed conditions not differing from each other in 15 men, even though only the early condition lowered mean fasting glucose against baseline. Both are small and short. The trial designed to settle it, a 162-person three-arm comparison of early TRE, late TRE and daily calorie restriction with body weight over 52 weeks as the primary outcome, has a primary completion date of March 2027.

The second is whether the window adds anything to a matched calorie prescription, and this is where Jamshed and Liu 2022 point in opposite directions. Both matched the calorie prescription. Jamshed found 2.3 kg more loss over 14 weeks with an early window; Liu found 1.8 kg more, not significant, over 12 months with an 08:00 to 16:00 window. The differences include duration, population, and what the control arm was doing, since Liu's control was actively calorie counting and Jamshed's was eating over a longer window with the same prescription. This page describes both rather than choosing.

There is also a direct counterweight to the early-window story that belongs here. Carlson 2007 held calories constant and moved all intake into a single late meal between 16:00 and 20:00, and morning glucose tolerance got worse. That is the same manipulation with the window at the other end of the day, and it is the most obvious candidate explanation for why placement might matter.

What happens to muscle

This is the field where the early window is least well characterised, and the honest answer is that the number most readers want does not exist in a verifiable form.

Jamshed 2022 reported weight, fat mass and the ratio of fat loss to weight loss. Weight loss favoured the early window by 2.3 kg, while the fat mass difference of 1.4 kg did not reach significance and the fat-to-weight-loss ratio did not differ. The trial did not establish that the extra 2.3 kg was fat, and it did not establish that it was lean mass either. A discrete lean mass figure is not in the abstract record and the full text was not retrievable during verification, so no number is published here. Steger's per-protocol analysis of the same trial found consistent adherers losing 2.8 kg of body fat against control adherers (P = 0.04), which is a fat mass result in a non-randomised subgroup rather than a lean mass one.

Sutton 2018 measured no body composition change because participants were fed to hold weight stable, which was the point of the design.

What can be said is what the wider literature says about compressed windows of this length. Cienfuegos found a 6-hour window losing 1.5 kg of lean mass against 1.4 kg of fat, with no training and no reported protein intake. Trials that ran 1.6 to 2.2 g/kg/day with supervised resistance training held fat-free mass at similar window lengths. Parr 2023 at 1.0 g/kg/day lost more lean mass while daily myofibrillar protein synthesis was unchanged at 1.28 versus 1.26 %/day. Protein intake and training track the outcome; window placement has not been tested against lean mass as a primary endpoint at all.

Doing it

Where the window sits
The trials used 07:00 to 15:00, 08:00 to 14:00 and 08:00 to 17:00, and the controlled-feeding trial finished dinner before 15:00. The measured insulin and blood pressure results belong to those placements, not to a window that merely starts earlier than usual.
Protein target
Neither eTRE trial reported protein in g/kg/day. Across the compressed-window literature, lean mass was held at 1.6 to 2.2 g/kg/day with resistance training and fell further at 1.0 g/kg/day, which makes total daily protein the number to watch when the last meal is mid-afternoon.
Watch sleep
The most adherent participants in the per-protocol analysis reported sleeping less and taking longer to fall asleep while reporting less fatigue. Both directions were measured in the same people.
Training timing
No eTRE trial supervised resistance training. In the trials that did, at other window placements, the arms that trained inside the feeding window held fat-free mass, and the one trial where the fasted arm trained before opening its window completed 374 fewer total repetitions and gained 4.0 kg less on the squat one-rep max (p = 0.05).
Expect the effect to be modest and real
The authors of the 14-week trial framed their own result as equivalent to cutting about 214 kcal/d. That is the scale of the thing.

Breaking the fast

An early window means the fast is broken at breakfast, which is the meal the dose-response work is least equivocal about. Postabsorptive myofibrillar synthesis does not differ between young and older adults, so the overnight fast has not suppressed protein synthesis; what feeding does is produce the rise. The rise takes at least 90 minutes to begin. In older adults the per-meal dose needed is larger, with 40 g beating 20 g after exercise, and one retrospective pooled reanalysis put the 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 reached it only when expressed per kilogram of lean body mass (p < 0.01).

Citations

  1. Human2018
    Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes

    Cell Metabolism

    5-week randomised crossover under isocaloric supervised feeding, 6-hour window with dinner before 15:00 versus 12 hours, in men with prediabetes. 8 completers, 12 enrolled, 130 screened. Compliance to provided meals 100%. Insulin resistance -36 U/mg (P = 0.005), insulinogenic index +14 U/mg (P = 0.05), morning systolic -11 and diastolic -10 mmHg (both P = 0.03), 8-isoprostane -11 pg/mL (P = 0.05) driven partly by worsening in the control arm. Glucose did not improve. No weight change by design.

  2. Human2022
    Effectiveness of Early Time-Restricted Eating for Weight Loss, Fat Loss, and Cardiometabolic Health in Adults With Obesity: A Randomized Clinical Trial

    JAMA Internal Medicine

    90 adults, mean BMI 39.6, 14 weeks, both arms receiving identical energy restriction and weight-loss counselling. A 07:00 to 15:00 window produced 2.3 kg more weight loss (95% CI -3.7 to -0.9; P = .002) and 4 mmHg better diastolic blood pressure (P = .04). Fat loss did not differ (-1.4 kg; P = .09) nor did the fat-to-weight-loss ratio (P = .43). Adherence 6.0 days per week. The authors framed the effect as equivalent to 214 kcal/d.

  3. Human2023
    Early time-restricted eating affects weight, metabolic health, mood, and sleep in adherent completers: A secondary analysis

    Obesity (Silver Spring)

    Per-protocol analysis of the same 90 participants, restricted to those adhering at least 5 days a week every week. Versus control adherers: weight -3.7 kg (P = 0.003), body fat -2.8 kg (P = 0.04), heart rate -7 beats/min (P = 0.02), insulin resistance -2.80 (P = 0.047), glucose -9 mg/dL (P = 0.047). Consistent adherers also self-reported sleeping less and taking longer to fall asleep. Not the randomised comparison.

  4. Human2019
    Time-Restricted Feeding Improves Glucose Tolerance in Men at Risk for Type 2 Diabetes: A Randomized Crossover Trial

    Obesity (Silver Spring)

    15 men at risk of type 2 diabetes, randomised crossover of early (08:00 to 17:00) and delayed (12:00 to 21:00) 9-hour windows, 7 days each with continuous glucose monitoring and a 2-week washout. Glucose incremental AUC fell (P = 0.001) and fasting triglycerides fell (P = 0.003) on day 7 versus day 0, with no mealtime by condition interactions in any variable. Mean fasting glucose was lower in the early condition (P = 0.02) but not the delayed (P = 0.17), with no difference between conditions.

  5. Human2022
    Randomized controlled trial for time-restricted eating in healthy volunteers without obesity

    Nature Communications

    90 randomised, 82 analysed, 5 weeks, three arms of early TRE, mid-day TRE and control in healthy adults without obesity. Early TRE was more effective than mid-day TRE at improving insulin sensitivity, the primary outcome. Early TRE alone improved fasting glucose, reduced total body mass and adiposity, reduced inflammation and increased gut microbial diversity. No serious adverse events. Outcome assessors blinded, participants not.

  6. Human2019
    Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in Humans

    Nutrients

    11 overweight adults, 4-day randomised crossover of 08:00 to 14:00 versus 08:00 to 20:00. The early window raised whole blood cell expression of the autophagy gene LC3A and of SIRT1 before breakfast (p < 0.04), raised MTOR in the evening (p = 0.007), and lowered mean 24-hour glucose by 4 mg/dL and glycaemic excursions by 12 mg/dL.

  7. Human2007
    Impact of reduced meal frequency without caloric restriction on glucose regulation in healthy, normal-weight middle-aged men and women

    Metabolism

    Cited here as the late-window counterweight. Randomised crossover, two 8-week periods at weight-maintenance calories taken either as three meals or as one meal between 16:00 and 20:00. On the single late meal, morning fasting glucose was higher, oral glucose tolerance test responses were greater and more sustained, and the insulin response was delayed. The impairment was reversible.

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.

  • Less fatigue during the day, reported in both the randomised and the per-protocol analyses
  • Shorter sleep and longer time to fall asleep in the most consistent adherers
  • Evening hunger as the hardest part, since the fast covers the usual social eating hours
  • Morning appetite growing over the first weeks

Sources: Uncontrolled self-report. The mood, fatigue and sleep items are participant-reported questionnaire outcomes inside Jamshed 2022 and its per-protocol secondary analysis, and the authors state that whether shortening sleep while reducing fatigue is healthful is not yet known. 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 taking an SGLT2 inhibitor without a prescriber stopping it first, because ketoacidosis can develop at a normal-looking blood glucose and a fingerstick will not warn you.
  • Anyone on insulin, a sulfonylurea or a meglitinide without a prescriber adjusting the dose, particularly since an early window puts the longest fasted stretch across the evening and overnight.
  • Pregnancy and breastfeeding.
  • Anyone with a history of an eating disorder or current loss-of-control eating.
  • Children and adolescents.
  • Anyone with a BMI under 18.5 or meeting the NICE refeeding risk criteria.
  • Shift workers and anyone whose working hours make a fixed early window impossible. This group has not been studied; a trial of personalised 10-hour eating in shift workers is running with a primary completion date of August 2028.
  • Anyone whose sleep is already fragile, given that the most adherent participants in the per-protocol analysis reported sleeping less and taking longer to fall asleep.

Questions

Is eating earlier actually better than eating later?
The two trials that tested it disagree. Xie 2022 found an early window improving insulin sensitivity more than a mid-day window in 82 analysed participants over 5 weeks. Hutchison 2019 found early and delayed 9-hour windows not differing from each other in 15 men over 7 days each, although only the early condition lowered mean fasting glucose against its own baseline. A 162-person trial comparing early TRE, late TRE and calorie restriction over 52 weeks has a primary completion date of March 2027.
What makes the controlled-feeding trial important?
Because it is the only trial in this literature that removed weight loss as an explanation. Meals were provided, matched meal by meal against the control arm, and participants were fed to hold weight stable. Insulin sensitivity, beta cell responsiveness, blood pressure and an oxidative damage marker still improved. It is also 8 completers, five weeks, men with prediabetes, and it reported a carryover effect after a 7-week washout.
Did the early window protect lean mass?
Not established either way. The 14-week trial reported weight, fat mass and the fat-to-weight-loss ratio, and a discrete lean mass figure is not in the abstract record and could not be verified, so this page does not publish one. The controlled-feeding trial produced no weight change by design. What the wider literature shows is that lean mass outcomes on compressed windows track protein intake and resistance training rather than window placement.