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Eating late increases hunger, decreases calories burned, and changes fat tissue

Eating later had profound effects on hunger and appetite-regulating hormones leptin and ghrelin, which influence our drive to eat. Specifically, levels of the hormone leptin, which signals satiety, were decreased across the 24 hours in the late eating condition compared to the early eating conditions.

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Obesity afflicts approximately 42 percent of the adult population and contributes to the onset of chronic diseases, including diabetes, cancer, and other conditions. While popular healthy diet mantras advise against midnight snacking, few studies have comprehensively investigated the simultaneous effects of late eating on the three main players in body weight regulation and thus obesity risk: regulation of calorie intake, the number of calories you burn, and molecular changes in fat tissue. A new study by investigators from Brigham and Women’s Hospital, a founding member of the Mass General Brigham healthcare system, found that when we eat significantly impacts our energy expenditure, appetite, and molecular pathways in adipose tissue. Their results are published in Cell Metabolism.

“We wanted to test the mechanisms that may explain why late eating increases obesity risk,” explained senior author Frank A. J. L. Scheer, PhD, Director of the Medical Chronobiology Program in the Brigham’s Division of Sleep and Circadian Disorders. “Previous research by us and others had shown that late eating is associated with increased obesity risk, increased body fat, and impaired weight loss success. We wanted to understand why.”

“In this study, we asked, ‘Does the time that we eat matter when everything else is kept consistent?’” said first author Nina Vujović, PhD, a researcher in the Medical Chronobiology Program in the Brigham’s Division of Sleep and Circadian Disorders. “And we found that eating four hours later makes a significant difference for our hunger levels, the way we burn calories after we eat, and the way we store fat.”

Vujović, Scheer and their team studied 16 patients with a body mass index (BMI) in the overweight or obese range. Each participant completed two laboratory protocols: one with a strictly scheduled early meal schedule, and the other with the exact same meals, each scheduled about four hours later in the day. In the last two to three weeks before starting each of the in-laboratory protocols, participants maintained fixed sleep and wake schedules, and in the final three days before entering the laboratory, they strictly followed identical diets and meal schedules at home.

In the lab, participants regularly documented their hunger and appetite, provided frequent small blood samples throughout the day, and had their body temperature and energy expenditure measured. To measure how eating time affected molecular pathways involved in adipogenesis, or how the body stores fat, investigators collected biopsies of adipose tissue from a subset of participants during laboratory testing in both the early and late eating protocols, to enable comparison of gene expression patterns/levels between these two eating conditions.

Results revealed that eating later had profound effects on hunger and appetite-regulating hormones leptin and ghrelin, which influence our drive to eat. Specifically, levels of the hormone leptin, which signals satiety, were decreased across the 24 hours in the late eating condition compared to the early eating conditions. When participants ate later, they also burned calories at a slower rate and exhibited adipose tissue gene expression towards increased adipogenesis and decreased lipolysis, which promote fat growth. Notably, these findings convey converging physiological and molecular mechanisms underlying the correlation between late eating and increased obesity risk.

Vujović explains that these findings are not only consistent with a large body of research suggesting that eating later may increase one’s likelihood of developing obesity, but they shed new light on how this might occur. By using a randomized crossover study, and tightly controlling for behavioral and environmental factors such as physical activity, posture, sleep, and light exposure, investigators were able to detect changes the different control systems involved in energy balance, a marker of how our bodies use the food we consume.

In future studies, Scheer’s team aims to recruit more women to increase the generalizability of their findings to a broader population. While this study cohort included only five female participants, the study was set up to control for menstrual phase, reducing confounding but making recruiting women more difficult. Going forward, Scheer and Vujović are also interested in better understanding the effects of the relationship between meal time and bedtime on energy balance.

“This study shows the impact of late versus early eating. Here, we isolated these effects by controlling for confounding variables like caloric intake, physical activity, sleep, and light exposure, but in real life, many of these factors may themselves be influenced by meal timing,” said Scheer. “In larger scale studies, where tight control of all these factors is not feasible, we must at least consider how other behavioral and environmental variables alter these biological pathways underlying obesity risk. ”

Beauty & Fashion

Redefining aesthetics: From anti-aging to healthy aging

Growing attention is now being given to healthy aging, understanding how the entire face changes over time, preserving facial harmony, and helping people continue to look like themselves.

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For decades, “anti-aging” has defined the beauty and aesthetics conversation, promising to erase wrinkles and reverse the signs of time. Today, that conversation is shifting.

Aging is no longer just about looking younger. Growing attention is now being given to healthy aging, understanding how the entire face changes over time, preserving facial harmony, and helping people continue to look like themselves.

A review published in Facial Plastic Surgery, The Anatomy of the Aging Face: A Review, describes aging as changes across bone, ligaments, muscles, fat, and skin. Another review in Aesthetic Surgery Journal, The Facial Aging Process From the “Inside Out”, explains how changes beneath the surface eventually become visible on top.

Studies in Plastic and Reconstructive Surgery show facial fat is organized into distinct anatomical compartments that can lose volume and shift position over time, altering facial shape and balance.

For multi-awarded aesthetic physician Dr. James Co, founder of Cosma Institute and Architect of Aesthetic Confidence, these findings are the reason aesthetic care must start with understanding, not just treating.

“Aging is not a disease we need to cure,” Co said. “It is a biological process. As physicians, our role is to understand what is changing beneath the surface, how those changes differ from person to person, and whether intervention is appropriate in the first place.”

“When you only look at the wrinkle, you are looking at the surface of a much bigger anatomical process,” he added. “The face ages as a system. Good assessment means understanding what is happening underneath before deciding what should be done on the surface.”

Part of that understanding is recognizing that no two faces age the same way. Two people can be the same age and experience aging very differently. Genetics, skeletal structure, fat distribution, skin characteristics, sun exposure, lifestyle, and environmental factors all influence how aging presents.

“Two patients can be the same age and come to me with completely different anatomy, lifestyles, concerns, and goals,” Co said. “Why would we expect their treatment plans to look exactly the same?”

This is where healthy aging broadens the conversation — from fixing isolated signs to looking at the face as a whole and listening to what the individual actually wants.

“Someone can want to look refreshed without wanting to look 20 years younger,” Co said. “Those are completely different goals.”

Rather than trying to freeze one version of the face forever, healthy aging acknowledges that the face will continue to change. As different structures change at different rates, the relationship between features evolves. Facial harmony is therefore not fixed.

“You cannot freeze one version of your face forever,” Co said. “But you can understand how the face is changing and make decisions that respect its natural proportions and your identity.”

In the age of social media, where aesthetic treatments are highly visible, Co cautions against self-diagnosis.

“Patients should not have to diagnose themselves from social media,” he said. “You might recognize a concern, but deciding why it is happening and what should be done about it requires proper assessment.”

The shift is also about how people feel, not just how they look. A 2022 review on minimally invasive facial aesthetic procedures found studies are increasingly looking beyond physical changes to include satisfaction with appearance and aspects of psychological and social well-being, while noting that evidence still needs careful interpretation.

For Co, this reinforces that success is not always about looking dramatically younger.

“We need to ask whether the result makes sense for the patient, whether expectations were met, and whether we preserved the things that make that person recognizable,” he said. “I would rather someone tell my patient, ‘You look well,’ than immediately ask, ‘What did you have done?'”

At Cosma Institute, Co applies this consultation-led philosophy through individualized assessment, facial harmony, medical judgment, and patient education. Having trained aesthetic practitioners across Southeast Asia and Europe, he advocates for natural-looking outcomes that respect the characteristics already present in each face — an approach that recently earned him two awards at the Merz Aesthetics Tala Awards.

For Co, the evolution of aesthetic medicine is not about having more tools, but knowing when to use them — and when not to.

“Aging cannot be stopped, and I don’t think that should be the promise,” he said. “What we can do is understand it better. We can look at the science, understand the anatomy, listen to the patient, and make decisions that allow them to age while still looking recognizably like themselves.”

For Co, healthy aging begins not with fighting age, but with understanding it.

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The look and feel of your neighborhood may affect your sleep

Those living in neighborhoods rated as having a stronger sense of safety tended to sleep longer, and that this rating appeared to be shaped by the streetscape.

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Your neighborhood’s “streetscape”—the physical environment of your street—is something that you have probably never consciously thought about, despite seeing it every day. But what if the streetscape was affecting you on a subconscious level and disrupting your sleep? 

This intriguing question is posed by the findings of a study led by Professor Daisuke Matsushita of the Graduate School of Human Life and Ecology at Osaka Metropolitan University. The research team used AI to analyze more than 200,000 Google Street View images to identify visual neighborhood characteristics. They then linked these characteristics to the self-reported sleep of 1,089 working adults living on the lower floors of apartments in Tokyo, who were most likely to be affected by the streetscape.  

They found that those living in neighborhoods rated as having a stronger sense of safety tended to sleep longer, and that this rating appeared to be shaped by the streetscape. Generally, people slept longer in areas with lots of greenery, such as leafy trees, on the street. Similarly, high “enclosure”—meaning many tall vertical buildings and few wide-open spaces—was also associated with longer sleep and fewer insomnia symptoms. 

However, the study also made a surprising finding. The researchers found that highly walkable streetscapes, such as those with more sidewalks and traffic signs, were associated with a lowered sense of safety and shortened sleep duration.  

This suggests that walkability does not always represent a reassuring environment. Instead, a possible explanation is that streets with extensive pedestrian infrastructure are often busier, more crowded, and used by more strangers, which may be perceived as less safe or less relaxing than quieter residential streets.  

“This study demonstrates the potential for evaluating streetscape characteristics across large geographic areas in a cost-effective manner,” Dr. Matsushita said. “Based on the technique used in this study, cities could potentially measure perceived safety, beauty, liveliness, and enclosure as well as pollution and noise.”  

“We hope that opening up this new perspective creates further possibilities for designing healthier neighborhoods,” he concludes.  

The findings were published in Building and Environment.

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Workout or nap? Either can help your sleepless brain, study finds

People who either completed 20 minutes of moderate-to-vigorous exercise or took a 90-minute nap performed about 22 per cent better on memory tests after 30 hours without sleep than those who did neither.

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A short workout or a nap can help protect memory after a sleepless night, a McGill University-led study has found.

Researchers found people who either completed 20 minutes of moderate-to-vigorous exercise or took a 90-minute nap performed about 22 per cent better on memory tests after 30 hours without sleep than those who did neither. The findings, published in Proceedings of the National Academy of Sciences (PNAS), point to practical ways to counter the effects of sleep deprivation.

“Sleep loss affects nearly every aspect of how we think and function, but many people can’t simply stop what they’re doing and get more sleep,” said senior author Marc Roig, Professor in McGill’s School of Physical and Occupational Therapy. “Our findings show that even a brief bout of exercise may help preserve one of our most important cognitive abilities.”

The study involved 54 healthy young adults who stayed awake for 30 consecutive hours under lab supervision. Participants were then assigned to one of three groups: a 20-minute cycling session, a 90-minute nap or a control condition. Three days later, researchers tested their memory for images they had viewed immediately after the intervention. Those who exercised or napped remembered significantly more images than participants who did neither.

Same result, different pathways

While the memory benefits were nearly identical, brain recordings revealed that exercise and napping helped in different ways.

Napping appeared to help the brain recharge, making it easier to take in and remember new information. Exercise, by contrast, helped the brain use its remaining resources more efficiently, without making participants feel more tired.

The findings could eventually inform fatigue-management strategies in workplaces where sleep loss is common and mistakes can have serious consequences, such as health care, transportation and emergency response.

“A nap isn’t always possible in the middle of a shift,” said first author Madhura Lotlikar, a doctoral candidate in McGill’s Department of Neurology and Neurosurgery. “Exercise is accessible, inexpensive and easy to implement. That makes it a promising tool to help people stay cognitively sharp when sleep is limited.”

The researchers emphasize that exercise cannot replace sleep, but it may help people function better when getting enough rest isn’t possible.

About the study

“Protecting episodic memory after sleep loss: Similar benefits of exercise and naps via distinct neural contributions” by Madhura Lotlikar and Marc Roig et al., was published in Proceedings of the National Academy of Sciences of the United States of America.

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