Your Sense of Smell May be the Key to a Balanced Diet

Lila Reynolds wrote . . . . . . . . .

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 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 took a scientific approach to baking, using a scale to measure the exact amount of icing to place on each cinnamon roll
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.”

Source: Northwestern University

The Sense of Smell in Older Adults Declines When It Comes to Meat, But Not Vanilla

That grandpa and grandma aren’t as good at smelling as they once were, is something that many can relate to. And, it has also been scientifically demonstrated. One’s sense of smell gradually begins to decline from about the age of 55. Until now, it was believed that one’s sense of smell broadly declined with increasing age. However, a study from the University of Copenhagen reports that certain food odors are significantly more affected than others.

The Department of Food Science’s Eva Honnens de Lichtenberg Broge and her fellow researchers have tested the ability of older Danes to perceive everyday food odors. The researchers measured how intensely older adults perceived different food odours, as well as how much they liked the odours.

“Our study shows that the declining sense of smell among older adults is more complex than once believed. While their ability to smell fried meat, onions and mushrooms is markedly weaker, they smell orange, raspberry and vanilla just as well as younger adults. Thus, a declining sense of smell in older adults seems rather odor specific. What is really interesting is that how much you like an odor is not necessarily dependent on theintensity perception” says Eva Honnens de Lichtenberg Broge.

For example, liking of seemed to be largely unaffected for fried meat, onions and mushrooms, despite the largest decline in intensity perception was seen for these specific odors. Also the ability to smell coffee declined, among other things, though they didn’t like the aroma of coffee to the same degree as younger adults.

The test subjects included 251 Danes between the ages of 60 and 98 and a control group consisting of 92 people between the ages of 20 and 39.


FOOD ODOURS FROM EVERYDAY LIFE

Instead of using odours of chemical origin, which is commonly the procedure when testing the sense of smell, Eva Honnens de Lichtenberg Broge developed a test kit including 14 natural food odours familiar from everyday life, including bacon, onions, toast, asparagus, coffee, cinnamon, orange and vanilla. The odours were made primarily from essential oils and presented to test subjects by sniffing sticks.


The food odours were chosen based upon commonly consumed foods and dishes that older people often eat and enjoy most according to meal plans and surveys from a Danish catering company that provides food for the elderly.

What’s the story?

The researchers can only speculate as to why the declining sense of smell in older adults seems to be odors specific, and why, in some cases, liking is largely unaffected. However, they can only speculate of why the intensity decline was most pronounced for fried meat, onions and mushrooms – foods that are referred to as ‘savory’ or umami in nature.

“This may be due to the fact that these are common food odours in which saltiness or umami is a dominant taste element. It is widely recognized that salty is the basic taste most affected by aging. Since taste and smell are strongly associated when it comes to food, our perception of aroma may be disturbed if one’s taste perception of saltiness is impaired to begin with,” explains Eva Honnens de Lichtenberg Broge.

Health and quality of life

The researchers hope that their findings can be deployed by those working to improve the meals and dining experiences of older adults. Figures show that half of those over 65 admitted to Danish hospitals are malnourished. The same applies to one in five nursing home residents.

While the sense of smell is important for stimulating appetite and our serotonin levels as well, according to Eva Honnens de Lichtenberg Broge, our study demonstrates that the sensitivity of one’s sense of smell need not be decisive. For several of the food odours, the respondent’s liking of an odour remained unchanged, even while their ability to perceive it had declined.

“Our results show that as long as a food odour is recognizable, its intensity will not determine whether or not you like it. So, if one wants to improve food experiences of older adults, it is more relevant to pay attention to what they enjoy eating than it is to wonder about which aromas seem weaker to them,” concludes Eva Honnens de Lichtenberg Broge.

The study is published in the scientific journal Food Quality and Preference.

Source: University of Copenhagen

Older Adults Having a Poor Sense of Smell May Face a Higher Risk of Pneumonia

Emilie Lorditch wrote . . . . . . . . .

An acute loss of smell is one of the most common symptoms of COVID-19, but for two decades it has been linked to other maladies among them Parkinson’s disease and dementia. Now, a poor sense of smell may signify a higher risk of pneumonia in older adults, says a team of Michigan State University researchers.

“About a quarter of adults 65 years or older have a poor sense of smell,” said Honglei Chen, a professor in the Department of Epidemiology and Biostatistics within Michigan State University College of Human Medicine. “Unlike vision or hearing impairment, this sensory deficit has been largely neglected; more than two-thirds of people with a poor sense of smell do not know they have it.”

In a first-of-its-kind study, Chen and his team found a possible link between poor sense of smell and a higher risk of pneumonia hospitalization. They analyzed 13 years of health data from 2,494 older adults, ages 71-82, from metropolitan areas of Pittsburgh, Pennsylvania, and Memphis, Tennessee. This study aimed to examine whether a poor sense of smell in older adults is associated with a higher future risk of developing pneumonia.

Chen’s research was published in the journal The Lancet Healthy Longevity.

The participants were given a Brief Smell Identification Test, or B-SIT, using common smells such as lemons and gasoline to determine if their sense of smell was good, moderate or poor. Then, the participants were monitored for the next 13 years using clinical exams and follow-up phone calls to identify hospitalization due to pneumonia.

The researchers found that compared with participants who had a good sense of smell, participants with a poor sense of smell were about 50% more likely to be hospitalized with pneumonia at any time point during the 13-year follow-up. Among participants (with a poor sense of smell) who never had had pneumonia before, the risk of having the first-ever pneumonia was about 40% higher.

“To our knowledge, this study provides the first epidemiological evidence that poor olfaction (sense of smell) is associated with a long-term higher risk of pneumonia in older adults,” said Yaqun Yuan, a postdoctoral fellow in Chen’s research group.

This study provides novel evidence that a poor sense of smell may have broader health implications beyond its connections to Parkinson’s disease and dementia.

“This is just an example of how little we know about this common sensory deficit,” Chen said. “Either as a risk factor or as a marker, poor sense of smell in older adults may herald multiple chronic diseases beyond what we have known about. To understand what this common sensory deficit means for our health, we need to think outside of the box.”

Source: Michigan State University

Loss of Sense of Smell as Marker of COVID-19 Infection

There is new evidence for the loss of smell as a symptom of COVID-19 infection. We are circulating the following intelligence to Public Health England with regards to anosmia. As a result, this information highlights the importance for healthcare personnel to employ full PPE and in turn help stem the rates of infection.

Post-viral anosmia is one of the leading causes of loss of sense of smell in adults, accounting for up to 40% cases of anosmia. Viruses that give rise to the common cold are well known to cause post-infectious loss, and over 200 different viruses are known to cause upper respiratory tract infections. Previously described coronaviruses are thought to account for 10-15% cases. It is therefore perhaps no surprise that the novel COVID-19 virus would also cause anosmia in infected patients.

There is already good evidence from South Korea, China and Italy that significant numbers of patients with proven COVID-19 infection have developed anosmia/hyposmia. In Germany it is reported that more than 2 in 3 confirmed cases have anosmia. In South Korea, where testing has been more widespread, 30% of patients testing positive have had anosmia as their major presenting symptom in otherwise mild cases.

In addition, there have been a rapidly growing number of reports of a significant increase in the number of patients presenting with anosmia in the absence of other symptoms – this has been widely shared on medical discussion boards by surgeons from all regions managing a high incidence of cases. Iran has reported a sudden increase in cases of isolated anosmia, and many colleagues from the US, France and Northern Italy have the same experience. I have personally seen four patients this week, all under 40, and otherwise asymptomatic except for the recent onset of anosmia – I usually see roughly no more than one a month. I think these patients may be some of the hitherto hidden carriers that have facilitated the rapid spread of COVID-19. Unfortunately, these patients do not meet current criteria for testing or selfisolation.

While there is a chance the apparent increase in incidence could merely reflect the attention COVID-19 has attracted in the media, and that such cases may be caused by typical rhinovirus and coronavirus strains, it could potentially be used as a screening tool to help identify otherwise asymptomatic patients, who could then be better instructed on self-isolation.

Given the potential for COVID-19 to present with anosmia, and the reports that corticosteroid use may increase the severity of infection, we would advise against use of oral steroids in the treatment of new onset anosmia during the pandemic, particularly if it is unrelated to head trauma or nasal pathology (such as nasal polyps).

There is potential that if any adult with anosmia but no other symptoms was asked to selfisolate for seven days, in addition to the current symptom criteria used to trigger quarantine, we might be able to reduce the number of otherwise asymptomatic individuals who continue to act as vectors, not realising the need to self-isolate. It will also be an important trigger for healthcare personnel to employ full PPE and help to counter the higher rates of infection found amongst ENT surgeons compared to other healthcare workers.

Source : ENTUK


Today’s Comic

What It’s Like to Live without a Sense of Smell

The smell of cut grass, freshly baked bread, childhood memories, lost loved ones. What happens when it’s all gone?

A new study from the University of East Anglia reveals the huge range of emotional and practical impacts caused by a loss of smell.

It finds that almost every aspect of life is disrupted – from everyday concerns about personal hygiene to a loss of sexual intimacy and the break-down of personal relationships.

Prof Carl Philpott, from UEA’s Norwich Medical School, led the research. Chris Hicks is a member of the poetry collective Aisle 16, which formed at UEA. He hasn’t been able to smell since birth.

Here’s what happened when the two experts met.

The researchers hope that their findings will help motivate clinicians to take smell problems more seriously, with better help and support offered to patients.

Prof Carl Philpott said: “Smell disorders affect around five per cent of the population and cause people to lose their sense of smell, or change the way they perceive odours. Some people perceive smells that aren’t there at all.

“There are many causes – from infections and injury to neurological diseases such as Alzheimer’s and as a side effect of some medications.

“Most patients suffer a loss of flavour perception which can affect appetite and can be made even worse if distortions in their sense of smell also co-exist.

“Previous research has shown that people who have lost their sense of smell also report high rates of depression, anxiety, isolation and relationship difficulties.

“We wanted to find out more about how a loss of smell affects people.”

The researchers worked with the Smell and Taste clinic at the James Paget University Hospital, Gorleston-On-Sea. The clinic opened in 2010 and was the UK’s first clinic dedicated to taste and smell.

The study involved 71 participants aged between 31-80 who had written to the clinic about their experiences. It was carried out in collaboration with Fifth Sense, the charity for people affected by smell and taste disorders.

The research shows that sufferers experience wide-ranging impairments to their quality of life. These included a negative emotional impact, feelings of isolation, impaired relationships and daily functioning, impacts on physical health and the difficulty and financial burden of seeking help.

In this podcast, Prof Philpott discusses his research with Chris – whose own personal experience of anosmia includes eating gone off meat, glugging chunky milk, intimacy problems and fear of sweating.

Prof Philpott said: “One really big problem was around hazard perception – not being able to smell food that had gone off, or not being able to smell gas or smoke. This had resulted in serious near misses for some.

“But smell is not just a life-saving sense – it is also life-enhancing.

“A large number of the participants no longer enjoyed eating, and some had lost appetite and weight. Others were eating more food with low nutritional value that was high in fat, salt and sugar – and had consequently gained weight.

“Participants had lost interest in preparing food and some said they were too embarrassed to serve dishes to family and friends which had an impact on their social lives.

“The inability to link smells to happy memories was also a problem. Bonfire night, Christmas smells, perfumes and people – all gone. Smells link us to people, places and emotional experiences. And people who have lost their sense of smell miss out on all those memories that smell can evoke.

“We found that personal hygiene was a big cause for anxiety and embarrassment, because the participants couldn’t smell themselves.

“Parents of young children couldn’t tell when their nappies needed changing, and this led to feelings of failure. One mother found it difficult bonding with her new baby because she couldn’t smell him.

“Many participants described a negative impact on relationships – ranging from not enjoying eating together to an impact on sexual relationships,” he added.

All of these problems led to diverse range of negative emotions including anger, anxiety, frustration, depression, isolation, loss of confidence, regret and sadness. And the problems were compounded by a lack of understanding about the disorder among clinicians.

Prof Philpott said: “The participants described a lot of negative and unhelpful interactions with healthcare professionals before coming to the James Paget Smell and Taste clinic. Those that did manage to get help and support were very pleased – even if nothing could be done about their condition, they were very grateful for advice and understanding.”

Duncan Boak, Founder and Chair of Fifth Sense, said: “Anosmia can have a huge impact on people’s quality of life in many ways, as this research demonstrates. An important part of Fifth Sense’s work is giving our beneficiaries a voice and the opportunity to change the way society understands smell and taste disorders, whether through volunteering or participating in research studies like this one. The results of this study will be a big help in our ongoing work to improve the lives of those affected by anosmia.”

‘Smell and taste disorders; a qualitative review’ is published in the journal Clinical Otolaryngology.

Source: University of East Anglia