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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.”

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Common drug class may increase risk of heart disease

The risk of cardiovascular disease increased in line with how much anticholinergic medication the participants used each year. Those with the highest exposure had a 71 per cent higher risk of a cardiovascular event than people who did not use anticholinergic medication at all.

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People who use drugs with anticholinergic effects, including certain antidepressants, drugs for urinary incontinence and common antihistamines, are at higher risk of developing cardiovascular disease.

This is shown in a study from Karolinska Institutet published in BMC Medicine.

Anticholinergic drugs reduce the effect of the neurotransmitter acetylcholine and are commonly prescribed to middle-aged and older people. This large group of drugs includes antihistamines used for allergic conditions, anxiety or insomnia, drugs for urinary incontinence, and certain antidepressants, where tricyclic antidepressants have a strong anticholinergic effect, whereas SSRIs have a weaker effect. A high cumulative use of these drugs, referred to as anticholinergic burden (see fact box), has previously been linked to impaired cognitive ability. 

May affect heart regulation 

The new study suggests that the drugs may also affect the parasympathetic nervous system and thereby the regulation of the cardiovascular system. The results show that it may be important to monitor the total drug burden in everyday clinical practice.

The study included more than 500,000 people in Stockholm, Sweden, who were 45 years of age or older and had no prior cardiovascular disease, except for hypertension, at the start of the study. The researchers followed the participants for up to 14 years and analysed how the use of anticholinergic drugs was associated with the development of cardiovascular disease.

“Many of these drugs are used by older people and by people with multiple medical conditions. We wanted to investigate whether the total exposure had any significance for the risk of developing cardiovascular disease over time,” says Nanbo Zhu, postdoctoral researcher at the Department of Neurobiology, Care Sciences and Society, Karolinska Institutet.

71 per cent higher cardiac risk

The study showed that the risk of cardiovascular disease increased in line with how much anticholinergic medication the participants used each year. Those with the highest exposure had a 71 per cent higher risk of a cardiovascular event than people who did not use anticholinergic medication at all. The association was seen for all types of cardiovascular disease but was particularly clear for heart failure and various forms of arrhythmia.

“Our results indicate that the cumulative drug burden can affect heart regulation, not only in the short term but also over the long term. This does not mean that the drugs should always be avoided, but that exposure should be monitored carefully,” says Hong Xu, assistant professor at the Department of Neurobiology, Care Sciences and Society.

The researchers point out that the study is observational, meaning it cannot establish a causal relationship. Other factors, such as underlying diseases, may also influence the associations.

The work was carried out within the Stockholm CREAtinine Measurements project in collaboration between several research groups at Karolinska Institutet and Region Stockholm. The study was funded by the Swedish Research Council, the Center for Innovative Medicine Foundation, and other foundations. Some researchers report assignments for the pharmaceutical industry, which are disclosed in the scientific publication.

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Mindfulness practices found to significantly reduce depression symptoms, especially for those with early-life adversity

Mindfulness interventions help by regulating our emotions better when different challenges come up. For someone who has experienced childhood neglect or abuse, mindfulness training can help us make sense of that and respond skillfully to this moment in time.

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A new study reveals that mindfulness practices may significantly reduce depression symptoms, particularly in people who have experienced early-life adversity, such as childhood abuse and neglect.

Led by Eric Loucks, professor of medicine, epidemiology, and of behavioral and social sciences and director of the Mindfulness Center at Brown, the study enrolled 201 participants, 101 of whom were randomized into the Mindfulness-Based Blood Pressure Reduction Program, while 100 were randomized into an enhanced usual care control, which included home blood-pressure monitors, physician access and health-education materials. Researchers also had a measure of participants’ early-life adversity, particularly their exposure to abuse or neglect.

Loucks and his team followed participants for six months to assess changes in blood pressure, health behaviors and mental health, finding that those in the mindfulness program showed significant improvements in their depression symptoms. Additionally, participants who experienced childhood neglect showed greater improvements in depression symptoms than those who had not. A similar, though less pronounced, trend was observed among people with a history of childhood abuse.

“In this program, that was primarily designed to lower blood pressure while addressing whole-person health, we also saw that mental well-being, particularly around depression symptoms, improved in participants that went through the program,” Loucks said. “The findings suggest that cultivating mindful self-regulation skills–such such as self-awareness, attention control and emotion regulation–may help interrupt maladaptive patterns shaped by past experiences.”

Over the last 15 years, Loucks has been studying social determinants of health such as early-life adversity and its impacts on cardiovascular health, body mass index and blood pressure. “I came to a point where I wanted to not just document it, but do something about it, and I wondered if mindfulness training might help,” he said. “I’d gone through a lot of mindfulness training myself outside of work and started to get trained up in mindfulness programs that are specific to health contexts.”

Loucks began to study the Mindfulness-Based Stress Reduction program, running it through two clinical trials that were funded by the NIH and finding that it reduced blood pressure in both trials. He also wanted to look at the intervention from a whole-person perspective.

“If we look at everyday folks out in the world, those that had exposure to early life adversity, like abuse and neglect, tend to have worse mental health and also worse cardiovascular health,” Loucks said. “Mindfulness interventions help by regulating our emotions better when different challenges come up. For someone who has experienced childhood neglect or abuse, mindfulness training can help us make sense of that and respond skillfully to this moment in time.” 

Loucks discussed this work during a keynote address at the U.S. DOHaD Society this year. “It felt like a coming-home moment to see that this intervention, originally developed to address psychosocial factors that influence health, had even stronger effects among people with early-life adversity, particularly on depression,” he said. “It’s been about a 15-year arc of research that culminated in these findings.”

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High-fiber diet linked to reduced risk of heart disease in night shift workers

A moderate intake of about 19 grams of fibre per day was linked to a lower risk for those who worked night shifts regularly. For those who worked night shifts sporadically, about 15 grams was enough. The current recommendation for adults is about 25 grams of dietary fibre per day.

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People who work at night have a higher risk of coronary artery disease, a type of heart disease. A new study suggests that a higher fibre intake in the diet may help reduce this risk. The study included over 220,000 adults in the UK and is published in the European Journal of Epidemiology.

The human body is built to sleep at night. This means that working during the night goes against this natural pattern, and can place additional strain on the body, including the heart. Previous research has linked night work to an increased risk of coronary artery disease. Since night work is often unavoidable, the researchers wanted to investigate whether certain dietary habits might have a protective effect.

More fibre associated with lower risk

The researchers used data from 220,000 adults in the UK Biobank (2006–2010) and divided the participants into three groups:

  • Day workers
  • Shift workers who worked night shifts sporadically
  • Regular night shift workers

The participants had completed a detailed questionnaire about their dietary habits. During a follow-up after about 12 years, it was found that night shift workers who consumed little fibre in their diet had a higher risk of coronary artery disease than those who consumed more fibre.

“A moderate intake of about 19 grams of fibre per day was linked to a lower risk for those who worked night shifts regularly. For those who worked night shifts sporadically, about 15 grams was enough. The current recommendation for adults is about 25 grams of dietary fibre per day,” says Diana Nôga, lead author and researcher at Uppsala University.

The researchers stress that the figures from the study are not official dietary recommendations. But they do show a pattern in this UK study: a higher dietary fibre intake was linked to a lower risk of heart disease among night shift workers.

“The link between fibre and a lower risk of heart disease is not just because those who eat more fibre generally have a healthier lifestyle. We know this because we adjusted for various lifestyle factors in the analysis. One possible explanation, supported by previous research, is that fibre in the diet can improve intestinal flora and also reduce lipids, which can be particularly good for the heart in people who work at night,” says Christian Benedict, senior author of the study and Professor of Pharmacology at Uppsala University.

Dietary fibre can support heart health

According to the researchers, an increased intake of fibre-rich foods such as whole grains, vegetables, fruit, legumes and lentils may be a simple way to improve heart health for night shift workers. However, this requires that you do not have any medical obstacles to doing this, such as chronic gastrointestinal diseases.

“Dietary changes should be seen as a complement to, not a substitute for, other heart health-promoting habits such as not smoking, remaining physically active, and getting enough sleep,” says Diana Nôga.

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