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Your sense of smell may be the key to a balanced diet

The food you ate just before your walk past the bakery may impact your likelihood of stopping in for a sweet treat – and not just because you’re full.

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Photo by Otto Norin from Unsplash.com

Walking past a corner bakery, you may find yourself drawn in by the fresh smell of sweets wafting from the front door. You’re not alone: The knowledge that humans make decisions based on their nose has led major brands like Cinnabon and Panera Bread to pump the scents of baked goods into their restaurants, leading to big spikes in sales.

But according to a new study, the food you ate just before your walk past the bakery may impact your likelihood of stopping in for a sweet treat – and not just because you’re full.

Scientists at Northwestern University found that people became less sensitive to food odors based on the meal they had eaten just before. So, if you were snacking on baked goods from a coworker before your walk, for example, you may be less likely to stop into that sweet-smelling bakery.

The study, “Olfactory perceptual decision-making is biased by motivational state,” was published August 26 in the journal PLOS Biology.

Smell regulates what we eat, and vice versa

The study found that participants who had just eaten a meal of either cinnamon buns or pizza were less likely to perceive “meal-matched” odors, but not non-matched odors. The findings were then corroborated with brain scans that showed brain activity in parts of the brain that process odors was altered in a similar way.

These findings show that just as smell regulates what we eat, what we eat, in turn, regulates our sense of smell.

Feedback between food intake and the olfactory system may have an evolutionary benefit, said senior and corresponding study author Thorsten Kahnt, an assistant professor of neurology and psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine.

“If you think about our ancestors roaming the forest trying to find food, they find and eat berries and then aren’t as sensitive to the smell of berries anymore,” Kahnt said. “But maybe they’re still sensitive to the smell of mushrooms, so it could theoretically help facilitate diversity in food and nutrient intake.”

Kahnt said while we don’t see the hunter-gatherer adaptation come out in day-to-day decision-making, the connection between our nose, what we seek out and what we can detect with our nose may still be very important. If the nose isn’t working right, for example, the feedback loop may be disrupted, leading to problems with disordered eating and obesity. There may even be links to disrupted sleep, another tie to the olfactory system the Kahnt lab is researching.

Using brain imaging, behavioral testing and non-invasive brain stimulation, the Kahnt lab studies how the sense of smell guides learning and appetite behavior, particularly as it pertains to psychiatric conditions like obesity, addiction and dementia. In a past study, the team found the brain’s response to smell is altered in sleep-deprived participants, and next wanted to know whether and how food intake changes our ability to perceive food smells.

According to Laura Shanahan, a postdoctoral fellow in the Kahnt lab and the first and co-corresponding author of the study, there’s very little work on how odor perception changes due to different factors. “There’s some research on odor pleasantness”, Shanahan said, “but our work focuses in on how sensitive you are to these odors in different states.”

Pizza and pine; cinnamon and cedar

To conduct the study, the team developed a novel task in which participants were presented with a smell that was a mixture between a food and a non-food odor (either “pizza and pine” or “cinnamon bun and cedar” – odors that “pair well” and are distinct from each other). The ratio of food and non-food odor varied in each mixture, from pure food to pure non-food. After a mixture was presented, participants were asked whether the food or the non-food odor was dominant.

Participants completed the task twice inside an MRI scanner: First, when they were hungry, then, after they’d eaten a meal that matched one of the two odors.

“In parallel with the first part of the experiment running in the MRI scanner, I was preparing the meal in another room,” Shanahan said. “We wanted everything fresh and ready and warm because we wanted the participant to eat as much as they could until they were very full.”

The team then computed how much food odor was required in the mixture in each session for the participant to perceive the food odor as dominant. The team found when participants were hungry, they needed a lower percentage of food odor in a mixture to perceive it as dominant – for example, a hungry participant may require a 50% cinnamon bun to cedar mixture when hungry, but 80% when full of cinnamon buns.

Through brain imaging, the team provided further evidence for the hypothesis. Brain scans from the MRI demonstrated a parallel change occurring in the part of the brain that processes odors after a meal. The brain’s response to a meal-matched odor was less “food-like” than responses to a non-matched meal odor.

Applying findings to future sleep deprivation research

Findings from this study will allow the Kahnt lab to take on more complex projects. Kahnt said with a better understanding of the feedback loop between smell and food intake, he’s hoping to take the project full circle back to sleep deprivation to see if lack of sleep may impair the loop in some way. He added that with brain imaging, there are more questions about how the adaptation may impact sensory and decision-making circuits in the brain.

“After the meal, the olfactory cortex didn’t represent meal-matched food odors as much as food anymore, so the adaptation seems to be happening relatively early on in processing,” Kahnt said. “We’re following up on how that information is changed and how the altered information is used by the rest of the brain to make decisions about food intake.”

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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