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Time-restricted7 studies in people 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

Your eating window moves to the start of the day and ends mid-afternoon. It is the only fasting plan with a study that fed people every meal, kept their weight steady on purpose, and still saw health markers improve. That study had eight people finish.

Overview

Early time-restricted eating puts the window early in the day. Jamshed 2022 used 7am to 3pm (07:00 to 15:00). The study that measured autophagy genes used 8am to 2pm (08:00 to 14:00). Sutton 2018 used a six-hour window with dinner done before 3pm (15:00). The idea behind it is the body clock: your body handles insulin better in the morning, and burns a little more energy digesting food then. But the reason it matters on this page is narrower.

It is the only plan where a study gave people every meal, matched each meal to the comparison group, and fed them enough to keep their weight steady. Insulin handling, the pancreas's insulin response, and blood pressure still got better. That design answers a question no at-home study can. It answered it in eight men with prediabetes.

Everything else here comes from people living at home, which gives the usual mix of weight change and self-reported eating.

How it works

Move the window earlier instead of making it shorter. In real life that means breakfast, lunch, an early dinner, and nothing after mid-afternoon.

People in Jamshed's study kept to it 6.0 days a week over 14 weeks. That is close to what studies of later windows report, so eating early did not clearly make it harder to stick with. In Sutton's study, people ate 100% of the meals they were given. That tells you about how the study was run, not about the plan.

A follow-up look at Jamshed's study found something worth saying next to the benefits. The people who stuck with it most closely said they slept less and took longer to fall asleep. They also said they felt less tired. The authors say plainly that nobody yet knows if sleeping less while feeling less tired is healthy.

What 18 hours actually reaches

Here is what a study measured when people were fed every meal and their weight did not change. Insulin resistance fell 36 U/mg. The body's early insulin response to food rose 14 U/mg. Morning blood pressure fell 11 mmHg on top and 10 mmHg on the bottom. A blood marker of wear and tear on cells (8-isoprostane) fell 11 pg/mL. Blood sugar did not improve over five weeks, and the authors say so plainly. The cell wear result was partly because that marker got worse in the comparison group. The fair reading is that the early window stopped a rise, not that it caused a drop. This is also the timing where the one direct measurement of autophagy (the cell's clean-up process) in people sits. In 11 overweight adults, four days of an 8am to 2pm window turned up the clean-up gene LC3A and a gene called SIRT1 in blood cells before breakfast. It turned up a gene called MTOR in the evening. Average blood sugar across 24 hours fell 4 mg/dL. Gene activity in blood cells is a sign, not a measure of the clean-up process itself. It is also not muscle or liver. Those are the places where fasting clearly boosts clean-up in animals, and nobody takes muscle or liver samples from healthy volunteers to check. No study in people has measured mitophagy (clean-up of the cell's power plants) on any fasting plan, at this timing or any other.

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

    Still digesting

    Burning
    Sugar from the meal you just ate. Insulin is high enough to keep fat locked away.
    • Insulin is at its after-meal peak. While it is up there, the enzyme that releases fat from fat cells stays switched off, so fat is being stored, not released.
    • The hour count on most fasting charts starts at the last bite. But the body is still digesting a mixed meal here, so the clock and what the body is doing are not yet the same thing.

    Read the biologyInsulin and insulin sensitivity during a fast

    Measured in people
    The hour-by-hour fasting studies in people start later than this. Klein 1993 took its first sample at 12 hours, in 6 healthy men. Rothman 1991 gives its first figure for new sugar making as an average across the first 22 hours. This row is the fed state those measurements are compared against. No measurement from a long fast falls inside it.

  2. 4h to 12h

    Meal digested, overnight fast

    Burning
    A mix of leftover sugar and fat. The liver keeps the brain supplied with sugar.
    Blood sugar
    5.58 mmol/L (100.5 mg/dL) at the 12 hour mark, in 6 healthy men
    Ketones
    Total ketones around 0.20 mmol/L after an overnight fast. That figure is acetoacetate and BHB added together, not BHB on its own.
    Insulin
    64.6 pmol/L (9.3 microunits/mL) at 12 hours, in the same 6 men
    • At 12 hours, glycerol is released at 2.08 and palmitic acid at 1.63 micromol/kg/min. These are two markers of fat being released. They are the starting numbers everything later in the fast is compared against.
    • Making new sugar from scratch already supplies most of the body's sugar at this point. It is not a backup waiting to be called on. This is the first place the popular "switch" story breaks down.

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

    Measured in people
    Klein 1993 measured blood sugar, insulin and fat release with tracers at 12 hours, in 6 healthy men. Féry 1983 measured total ketones in people after an overnight fast and put the starting level at 0.20 mmol/L. Rothman 1991 measured liver glycogen again and again with a special MRI scan through a 68 hour fast in healthy adults. It worked out that new sugar making supplied 64% of all the body's sugar across the first 22 hours.

  3. 12h to 18h

    Ketones have not moved yet

    Burning
    Fat use rising. More and more of the body's sugar is being made fresh, not pulled from storage.
    Ketones
    A middle change of 0% between 12 and 18 hours, measured every 6 hours in 34 adults
    • BHB, the main ketone, does not move in this window. In 34 adults sampled every 6 hours through the standard 72 hour fast doctors use for testing, the middle change from 12 to 18 hours was zero.
    • Making new sugar supplies 64% of the body's sugar across the first 22 hours. A second, unrelated method put it at about 47% by 14 hours. The body does not switch from stored sugar to fat at a set hour.
    • In 11 overweight adults, activity of the autophagy gene LC3A in blood cells was 22% higher after an 18 hour fast than after a 12 hour fast. In the same people, activity of the MTOR gene also rose, by 9%.

    Read the biologyGlycogen depletion and gluconeogenesisKetogenesis and beta-hydroxybutyrateAutophagy

    Measured in people
    Service 2005 measured BHB every 6 hours in 34 adults whose 72 hour test fasts came back clear for a rare insulin-making tumour. Rothman 1991 measured the share of new sugar making with a special MRI scan. Jamshed 2019 measured gene activity in blood cells in an 11-person, 4 day study where each person tried two eating windows: 8am to 2pm, and 8am to 8pm. That is one gene's activity in blood cells. It is not the real speed of autophagy, and it is not muscle. No study in any species has tested a 16 hour time point for autophagy.

  4. 18h to 1d

    The biggest hours for fat release

    past this window
    Burning
    Fat and glycerol, with ketone making starting its climb
    Ketones
    Climbing. The middle rise from 18 to 36 hours was +333%, the steepest stretch of a 72 hour fast.
    Insulin
    70% of the whole drop seen across a 72 hour fast has already happened by 24 hours
    • The single biggest jump in fat release across a whole 72 hour fast comes between 18 and 24 hours. 60% of the total rise in fat release happens between 12 and 24 hours. The authors put that down to falling insulin, not to any change in blood sugar.
    • In a study of 30 healthy adults, growth hormone was clearly higher after a 24 hour water-only fast than after a normal eating day. Each person did both. The size of that rise is not in the published summary, so it is not given here.
    • In the same study, haemoglobin, red blood cell count and haematocrit all rose together at 24 hours. That pattern means the fluid part of the blood shrank. It does not mean new red blood cells were made.
    • In 20 volunteers, energy burned over 24 hours, measured in a sealed room, fell during a 24 hour fast. How much it fell varied from person to person.

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

    Measured in people
    Horne 2013 had 30 seemingly healthy adults do both a 24 hour water-only fast and a normal eating day, in random order. It measured growth hormone, blood counts, cholesterol, triglycerides, bicarbonate and weight. Klein 1993 measured fat release with tracers. Hollstein 2020 measured energy burned over 24 hours in a sealed room in 20 volunteers. The exact percentage drop is not in the published summary, so it is not given here. On autophagy, a 24 hour fast raised p62 (also called SQSTM1) in the thigh muscle of 50 women. That points toward less recycling in muscle, not more.

  5. 1d to 36h

    Thyroid drops before metabolic rate does

    past this window
    Burning
    Fat. The remaining sugar is built from glycerol, lactate and protein building blocks.
    Ketones
    1.308 mmol/L on average after day 1, in 13 men starting a 10 day water fast, up from 0.177 at the start. People varied a lot: the spread around that average (1.053) was nearly as big as the average itself.
    • Making new sugar supplies 82% of the body's sugar between 22 and 36 hours.
    • In 8 healthy men, the thyroid hormone T3 fell from 2.30 to 1.84 nmol/L by 30 hours. TSH, the hormone that tells the thyroid to work, fell below 1 mU/L, and its usual night-time peak disappeared. Blood cortisol did not change.
    • So the thyroid slows down within the first 30 hours, well before anyone can measure a drop in resting metabolic rate.
    • Salt loss has not turned yet. In 9 women with obesity who kept eating their usual amount of salt while fasting, salt in the urine started to rise after about 48 hours and then went above what they took in.

    Read the biologyGlycogen depletion and gluconeogenesisKetogenesis and beta-hydroxybutyrateAutophagy

    Measured in people
    Rothman 1991 measured the share of new sugar making with a special MRI scan in healthy adults. Hugues 1984 fasted 8 healthy men for 30 hours and tested their thyroid hormones again and again. Dai 2022 measured blood BHB daily in 13 men fasting in a supervised facility. Sigler 1975 collected urine in 3 hour blocks from 9 women with obesity on a hospital ward. On autophagy, the only study in people with several time points in one fast took thigh muscle samples at 2, 12, 24 and 36 hours. The markers LC3I, LC3II and p62 all fell, but only in untrained people. The authors sum it up as muscle recycling being only mildly affected by 36 hours of fasting.

What studies in people found

There is one study where people were fed every meal and ate the same calories either way. There is one 14-week study where both groups cut the same calories, plus a follow-up look at the people in it who stuck with it best. And there are two studies where the same people tried early and later windows.

  • Jamshed 2022, 90 adults at a university weight loss clinic for 14 weeks. Their average BMI was 39.6. Everyone cut calories and got weight loss care. A 7am to 3pm window gave 2.3 kg more weight loss than eating over 12 hours or more on the same calorie cut. The bottom blood pressure number was 4 mmHg better. Tiredness, energy and low mood scores improved. Fat loss did not clearly differ (1.4 kg), and neither did the share of weight lost as fat. The authors said the effect was about the same as cutting 214 calories a day.
  • Xie 2022, 90 healthy adults without obesity for 5 weeks (82 analysed). An early window improved insulin handling more than a mid-day window. Only the early window improved fasting blood sugar, lowered body weight and body fat, lowered inflammation and made gut bacteria more varied. The people measuring results did not know who was in which group. The people taking part did.
  • Steger 2023, a second look at the same 90 people in Jamshed's study. It only counted people who kept to the plan at least 5 days every week. Compared with people who kept to the comparison plan: weight fell 3.7 kg more, body fat 2.8 kg more, heart rate 7 beats a minute more, insulin resistance 2.80 more, and blood sugar 9 mg/dL more. These people also said they slept less and took longer to fall asleep. This tells you what happens in people who stick with it, not what happens when it is simply handed out.
  • Hutchison 2019, 15 men at risk of type 2 diabetes. Each man tried an early 8am to 5pm window (08:00 to 17:00) and a late noon to 9pm window (12:00 to 21:00) for 7 days each, wearing glucose monitors. How well they handled sugar got better, and fasting blood fats fell, on both windows compared with where they started. Average fasting blood sugar was lower on the early window only. But the two windows did not differ from each other, so this study does not show early beats late.
  • Sutton 2018, men with prediabetes. 12 started so that 8 would finish, which is how many the study needed. Each man tried both plans for 5 weeks. They were given every meal, matched meal by meal, and ate them in the clinic or on live video. Insulin resistance fell 36 U/mg, the early insulin response to food rose 14 U/mg, and morning blood pressure fell 11 over 10 mmHg. The cell wear marker fell about 14% compared with the other plan. Artery stiffness and LDL and HDL cholesterol did not improve. Morning resting heart rate, blood fats and total cholesterol went up or tended to go up.

What this does not tell you: The fed-every-meal study had 8 people finish and a known carry-over effect. After a 7-week break, all but one man who did the early window first started the second plan with insulin after meals at least 25% below where he began. Jamshed's study does not give a lean mass number in the summary we could check, so this page does not print one. Hutchison ran 7 days per window in 15 men. Xie ran 5 weeks in healthy people without obesity.

Reading the research record

Two questions are open here, and the studies truly split on both.

The first is whether an early window beats a later one. Xie 2022 found early beat mid-day for insulin handling, in 82 people. Hutchison 2019 found early and late windows did not differ from each other in 15 men, though only the early window lowered fasting blood sugar compared with where they started. Both studies are small and short. The study built to settle it has 162 people in three groups: early window, late window, and daily calorie cutting. It tracks weight over 52 weeks, and its main results are due in March 2027.

The second is whether the window adds anything when both groups cut the same calories. Here Jamshed and Liu 2022 point opposite ways. Both gave both groups the same calorie target. Jamshed found 2.3 kg more loss over 14 weeks with an early window. Liu found 1.8 kg more over 12 months with an 8am to 4pm window, which was too small to count as a real difference. The studies differ in length, in who took part, and in what the comparison group did. Liu's comparison group was counting calories. Jamshed's was eating over a longer window on the same calorie target. This page describes both and does not pick.

There is also a direct counterweight to the early-window story. Carlson 2007 kept calories the same and moved all eating into one late meal between 4pm and 8pm (16:00 to 20:00). Morning blood sugar handling got worse. That is the same change with the window at the other end of the day. It is the most obvious reason to think timing might matter.

What happens to muscle

This is where the early window is least well understood. The plain answer is that the number most readers want does not exist in a form we could check.

Lean mass means the non-fat part of you, mostly muscle and water. Jamshed 2022 reported weight, fat, and the share of weight lost as fat. The early window lost 2.3 kg more weight. The 1.4 kg fat difference was too small to count as real, and the share lost as fat did not differ. The study did not show that the extra 2.3 kg was fat. It did not show it was lean mass either. There is no lean mass number in the summary, and we could not get the full paper to check, so no number is printed here.

Steger's second look at the same study found that people who stuck with it best lost 2.8 kg more body fat than people who stuck with the comparison plan. That is a fat result in a hand-picked group, not a lean mass result.

Sutton 2018 measured no body change, because people were fed to keep their weight steady. That was the point of the design.

What can be said is what the wider research shows for short windows like this. Cienfuegos found a 6-hour window lost 1.5 kg of lean mass and 1.4 kg of fat, with no weight training and no protein reported. Studies that fed 1.6 to 2.2 g of protein per kg of body weight a day, with supervised weight training, kept lean mass at similar window lengths. Parr 2023, at 1.0 g per kg a day, lost more lean mass while daily muscle building stayed the same: 1.28 against 1.26 %/day. Protein and training track the result. Nobody has tested window timing against lean mass as the main question.

Doing it

Where the window sits
The studies used 7am to 3pm, 8am to 2pm and 8am to 5pm (07:00 to 15:00, 08:00 to 14:00 and 08:00 to 17:00). In the fed-every-meal study, dinner was done before 3pm. The insulin and blood pressure results belong to those times, not to any window that just starts a bit earlier than usual.
Protein target
Neither early-window study reported protein per kg of body weight. Across short-window studies, people kept lean mass at 1.6 to 2.2 g per kg a day with weight training and lost more at 1.0 g per kg a day. So when your last meal is mid-afternoon, total daily protein is the number to watch.
Watch sleep
The people who stuck with it most closely said they slept less and took longer to fall asleep, while feeling less tired. Both were measured in the same people.
Training timing
No early-window study had people lift weights with supervision. In studies that did, with other window times, the groups that trained inside their eating window kept lean mass. In the one study where the fasting group trained before its window opened, they did 374 fewer total reps and gained 4.0 kg less on their best squat.
Expect the effect to be modest and real
The authors of the 14-week study said their result was about the same as cutting 214 calories a day. That is the size of the thing.

Breaking the fast

An early window means you break the fast at breakfast. That is the meal where the protein research is clearest. After an overnight fast, muscle building ticks along at the same rate in young and older adults. So the overnight fast has not shut muscle building down. What eating does is give it a boost, and that boost takes at least 90 minutes to start. Older adults need more protein per meal: after exercise, 40 g beat 20 g. One study that pooled and re-checked older data put the top useful amount at 0.40 g per kg of body weight in older men and 0.24 in younger men. That difference was not clearly real. It only became clear when counted per kg of lean body mass.

Sources

  1. Study in people2018
    Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes

    Cell Metabolism

    Men with prediabetes each spent 5 weeks eating in a 6-hour window with dinner before 15:00 and 5 weeks over 12 hours, on the same food, all supplied and all eaten. 12 started and 8 finished, out of 130 screened. The early window improved the insulin response and cut morning blood pressure by 11 (top) and 10 (bottom) mmHg, with no weight change. Blood sugar did not improve, and part of a drop in a cell damage marker came from the comparison phase getting worse.

    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. Study in people2022
    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 with obesity, average BMI 39.6, spent 14 weeks on the same calorie cut and the same coaching. Eating only from 07:00 to 15:00 gave 2.3 kg more weight loss and 4 mmHg better lower blood pressure. Fat loss did not clearly differ, and neither did the share of weight lost as fat. People kept the window 6.0 days a week, and the authors said the effect was like eating 214 fewer calories a day.

    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. Study in people2023
    Early time-restricted eating affects weight, metabolic health, mood, and sleep in adherent completers: A secondary analysis

    Obesity (Silver Spring)

    A second look at the same 90 people, counting only those who kept their plan at least 5 days every week. The early window group lost 3.7 kg more weight and 2.8 kg more body fat, and their heart rate, blood sugar and insulin resistance fell. They also said they slept less and took longer to fall asleep. This is not the fair head-to-head comparison the study was built on.

    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. Study in people2019
    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 each tried an early 9-hour window (08:00 to 17:00) and a late one (12:00 to 21:00) for 7 days, wearing glucose monitors. Blood sugar after meals and fasting blood fats fell with both windows by day 7. Morning blood sugar fell only with the early window. Still, early and late did not differ from each other on anything measured.

    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. Study in people2022
    Randomized controlled trial for time-restricted eating in healthy volunteers without obesity

    Nature Communications

    90 healthy adults without obesity spent 5 weeks on an early window, a mid-day window, or no change, and 82 were counted. The early window beat the mid-day window at improving how the body handles insulin, the main thing measured. Only the early window also improved fasting blood sugar, weight, body fat, inflammation and gut bacteria variety. There were no serious side effects.

    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. Study in people2019
    Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in Humans

    Nutrients

    11 adults with overweight each spent 4 days eating from 08:00 to 14:00 and 4 days eating from 08:00 to 20:00. The early window lowered average blood sugar over 24 hours by 4 mg/dL and cut swings by 12 mg/dL. It also raised the activity of a cell clean-up (autophagy) gene and an ageing-related gene in blood cells.

    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. Study in people2007
    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. Healthy, normal-weight middle-aged adults ate their usual calories as three meals for 8 weeks and as one meal between 16:00 and 20:00 for 8 weeks. On the single late meal, morning blood sugar was higher, blood sugar rose more and stayed up longer after a sugar drink, and insulin was slow to respond. It all went back to normal afterwards.

    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 things people say about their own fasting. Nobody checked them, so they are not evidence. They are here because they tell you what to expect and what to watch for, which the studies do not. They cannot tell you whether anything works.

  • Feeling less tired during the day. This came up in both the full study and the follow-up look at people who stuck with it.
  • Shorter sleep and taking longer to fall asleep, in the people who stuck with it most closely.
  • Evening hunger as the hardest part, since the fast covers the usual social eating hours.
  • Morning appetite growing over the first weeks.

Sources: These are self-reports with no comparison group. The mood, tiredness and sleep items come from questionnaires people filled out inside Jamshed 2022 and its follow-up look. The authors say nobody yet knows if sleeping less while feeling less tired is healthy. A separate review of what fasting communities report is still being put together, and nothing here comes from it.

Who this is wrong for

  • Anyone taking an SGLT2 inhibitor, unless a prescriber stops it first. It can cause ketoacidosis (a dangerous acid build-up) while blood sugar looks normal, and a finger-prick test will not warn you.
  • Anyone on insulin, a sulfonylurea or a meglitinide, unless a prescriber changes the dose. This matters more here, because an early window puts your longest stretch without food across the evening and night.
  • Pregnancy and breastfeeding.
  • Anyone with a past eating disorder, or who now has episodes of eating they cannot control.
  • Children and teens.
  • Anyone with a BMI under 18.5, or who meets the UK NICE risk list for refeeding problems.
  • Shift workers, and anyone whose work hours make a fixed early window impossible. Nobody has studied this group yet. A study of 10-hour windows in shift workers is running, with main results due in August 2028.
  • Anyone whose sleep is already shaky. The people who stuck with it most closely said they slept less and took longer to fall asleep.

Questions

Is eating earlier actually better than eating later?
The two studies that tested it disagree. Xie 2022 found an early window improved insulin handling more than a mid-day window, in 82 people over 5 weeks. Hutchison 2019 found early and late 9-hour windows did not differ from each other, in 15 men over 7 days each. Only the early window lowered fasting blood sugar compared with where those men started. A study of 162 people comparing an early window, a late window and calorie cutting over 52 weeks has main results due in March 2027.
What makes the controlled-feeding trial important?
It is the only study in this field that ruled out weight loss as the reason for the results. People were given every meal, matched meal by meal to the comparison plan, and fed enough to keep their weight steady. Insulin handling, the pancreas's insulin response, blood pressure and a marker of cell wear still improved. It also had only 8 people finish, lasted five weeks, studied men with prediabetes, and found a carry-over effect after a 7-week break.
Did the early window protect lean mass?
Nobody knows either way. The 14-week study reported weight, fat, and the share of weight lost as fat. It has no lean mass number in the summary, and we could not check one, so this page does not print one. The fed-every-meal study had no weight change on purpose. The wider research shows that lean mass on short windows tracks protein and weight training, not window timing.