Adults who limited daily food intake to an earlier window ending around 5:30 p.m. experienced greater reductions in abdominal subcutaneous fat and improvements in fasting and overnight glucose in a randomized trial of time-restricted eating.
By yourNEWS Media Newsroom
Eating earlier in the day may provide metabolic advantages beyond the weight loss associated with time-restricted eating alone, according to a study published in Nature Medicine that compared different daily fasting schedules among adults with obesity.
Researchers from the University of Granada and collaborating institutions found that participants assigned to an early eating window — typically from about 9:45 a.m. until 5:30 p.m. — experienced greater reductions in abdominal subcutaneous fat and better blood glucose regulation than participants following later or differently timed eating schedules.
Nearly 200 adults between ages 30 and 60 with a body mass index above 32 participated in the randomized trial.
Participants were divided among four groups: an early time-restricted eating schedule, a late schedule, a self-selected eating window or usual care.
The early group ate during a median window of approximately 9:45 a.m. to 5:30 p.m. The late group generally ate between 2:20 p.m. and 9:30 p.m., while participants in the self-selected group chose their own daily eating periods.
All participants received guidance on healthy lifestyles and the Mediterranean diet.
Across the time-restricted eating groups, participants lost an average of approximately 3 to 4 kilograms, or roughly 6.6 to 8.8 pounds, according to the researchers.
The early-eating group, however, showed additional changes that were not observed to the same degree in the other groups.
Investigators reported a greater reduction in abdominal subcutaneous fat, the layer of fat stored directly beneath the skin, along with significant improvements in fasting glucose and overnight glucose levels.
Study co-lead author Jonatan R. Ruiz, PhD, said the trial was designed in part to determine whether findings involving circadian rhythms in animal research would translate to humans.
“We wanted to investigate whether these findings translate to humans and how the timing of the eating window — early, late, or self-selected — affects weight loss, fat distribution, and cardiometabolic health in men and women with overweight or obesity,” Ruiz told Medical News Today.
Time-restricted eating is a form of intermittent fasting in which all daily food consumption occurs within a specified number of hours.
Rather than necessarily prescribing a particular calorie target, the approach focuses primarily on when food is eaten.
Megan Ramos, author of “Intermittent Fasting for Optimal Health Transforming Your Metabolism and Reversing Chronic Disease,” has described time-restricted eating as limiting food consumption to designated hours each day.
The timing may matter because the human body processes food differently across the circadian cycle.
Earlier research has suggested that consuming meals in the morning and around midday can produce a more favorable metabolic response than eating the same foods later in the day, including lower post-meal glucose levels and reduced fat accumulation.
Other studies examining eating windows ending before approximately 5 p.m. have similarly reported stronger effects on weight and glucose regulation than later schedules.
Researchers in the Nature Medicine trial assessed body weight, abdominal fat distribution and multiple cardiometabolic measurements, including fasting and overnight glucose.
Previous work examining early time-restricted eating has also documented improvements in insulin sensitivity, blood pressure and oxidative stress, even in circumstances where weight loss was not the only factor being studied.
The latest findings add evidence that aligning eating periods more closely with the body’s natural day-night cycle may influence where fat is stored and how effectively the body regulates glucose.
“The greater reduction in abdominal subcutaneous fat observed in the early fasting group highlights the potential metabolic advantages of aligning food intake with the body’s natural circadian rhythms,” Ruiz said.
Research involving eating windows such as 8 a.m. to 4 p.m. has previously suggested improvements in insulin sensitivity, fat metabolism and cellular processes compared with consuming food later in the day.
Intermittent fasting has also been investigated for its potential effect on visceral fat, the deeper abdominal fat that surrounds internal organs and is associated with increased risks of Type 2 diabetes, cardiovascular disease and chronic inflammation.
The latest trial specifically reported a greater decrease in subcutaneous abdominal fat in the early group.
Outside experts said the findings were encouraging while noting that additional research is needed.
Dr. Mir Ali, a bariatric surgeon at MemorialCare Surgical Weight Loss Center in Fountain Valley, California, characterized the study positively but said its relatively small sample size was a limitation.
“Continued research will define those benefits further and help delineate the optimal fasting schedule,” Ali said.
He also said future studies could examine how different forms of time-restricted eating interact with different dietary patterns.
Registered dietitian nutritionist Monique Richard, MS, RDN, LDN, emphasized that people interested in time-restricted eating should choose a schedule they can realistically maintain while still meeting their nutritional needs.
She suggested monitoring factors such as mood, energy and cognitive performance over a period of four to six weeks.
“If your work and social schedule allow, choose a time to declare ‘kitchen closed,’ or eating time is done for the day,” Richard said.
Shorter daily fasting periods may be easier for some people to integrate into work and family routines than longer or extended fasts.
Researchers and fasting advocates have also examined whether periods without food may affect inflammation and cellular repair processes. A report from Mercola.com has similarly described fasting as a longstanding health practice with potential effects on inflammation and cellular maintenance.
Those broader claims extend beyond the specific findings of the Nature Medicine trial, which concentrated on weight, body-fat distribution and cardiometabolic measurements.
The researchers plan to examine additional questions, including whether time-restricted eating has long-term effects on bone density.
They also intend to study whether combining exercise with restricted eating windows produces greater improvements than either strategy alone in body weight, body composition, ectopic fat and cardiometabolic health.
The trial does not establish the long-term health consequences of maintaining an early eating schedule for years.
Other research comparing time-restricted eating with conventional calorie restriction has found that both approaches can reduce fasting glucose, HbA1c, body weight and waist circumference without consistently demonstrating that one strategy is superior across every outcome.
The current findings nevertheless suggest that the clock may be an important variable.
All of the fasting groups lost more weight than participants receiving usual care, but the early group showed the clearest additional advantages in abdominal subcutaneous fat and glucose regulation.
For people considering time-restricted eating, the findings indicate that ending food intake earlier in the day may offer metabolic benefits that are not captured by simply shortening the eating window without regard to when it occurs.
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