Dose smell impact hunger, appetite, and weight? What’s the evidence?
During my morning ritual of reading through all the latest health and medical headlines and new research releases, one particular news brief from Science Daily caught my eye: “New device could help improve taste of foods low in fat, sugar and salt.” The summary read:
Scientists may be closing in on a way to let consumers savor the sweet taste of cake, cookies and other delights without the sugar rush. They have isolated several natural aromatic molecules that could be used to trick our brains into believing that desserts and other foods contain more fat, sugar or salt than they actually do.
A combination of aromatic molecules, the psychology of food preferences, and brain biochemistry! I had a hit! Immediately, questions emerged in my head:
“Could aromas make healthful foods more appealing and decrease some of the addictive properties of certain foods (many manufactured to be that way)?”
“Could essential oils be a potential tool to deal with the obesity epidemic?”
Sometimes, my thoughts jump ahead of my eyes.
I read on:
Aroma plays a vital role in how we perceive food (just try pinching your nose closed while you eat — odds are you won’t taste anything). Based on this fact, food scientists have long used chemical aromatics, essential oils and botanical extracts to enhance the flavor of food and beverages to boost sales.
The study was fascinating. It even involved the smell of ham. (Bacon lovers and haters, do I have your attention?)
In short, these researchers were able to isolate several natural aromatic molecules that could be used to trick our brains into believing that desserts and other foods contain more fat, sugar, or salt than they actually do. This in turn, can impact appetite.
This new trial was based on the scientists’ original research on how smell effects taste perception. It consisted of a flan dish with no salt. The participants were instructed to eat the flan with varying amounts of ham and salt aroma. They found that the ham aroma and varying degrees of salt smell fooled the subjects to believe they were eating salty flan, even though there was no salt! (Do you sense a bias of appetite decreasing in vegetarians?)
Now, the French scientists were able to create a new device called a Gas Chromatograph-Olfactometry Associated Taste (GC-OAT). For the experiment, they combined this techy tool with an olfactoscan to produce a continuous stream of aromas through a tube to a subject’s nose. Here’s how this experiment went and the ham factor was eliminated:
Participants were asked to smell real fruit juice aroma through the olfactoscan. Meanwhile, the researchers used the GC-OAT to isolate molecules from the juice. Then, they added the molecules one at a time into the olfactoscan tube. As the participants smelled each of these mixtures, they were asked if the molecule contributed to their perceived sweetness of the fruit juice. Thomas-Danguin says the preliminary results suggest that this new technique could eventually help food manufacturers better formulate more healthful foods without sacrificing taste, aroma or texture of the original products.
Scientists will be presenting their exciting discovery at the National Meeting and Exposition of the American Chemical Society (ACS). I will be on the lookout for the published results as the possibilities to me are very exciting!
I have been reviewing recently the subject of food addiction and unhealthy patterns. It has always been an interest of mine (see some of my previous blogs), This is due to the fact that diet is such an important component of health, yet some people tend to have blocks in implementing more nurturing food patterns for themselves. Therefore, I have always been interested in tools and factors that support cravings and willpower. These include addressing: biochemical differences in brain signaling, hormonal imbalances, sleep, lifestyle, nutrient deficiencies, digestive disturbances, emotional connections to food, and education on eating foods that are designed to be addictive without consumer’s knowledge. This all helps me tailor a specific and personalized dietary and wellness plan unique to the individual. Still, results only last as long as biochemistry is balanced with emotional cues. (Click here to read the latest results of a personalized study in nutrition.)
So, let’s explore how our nose may assist with making better choices with food and modulate appetite. We may not even need a fancy, smancy new device to take advantage of the application!
The Power of Smell
Last week, I explored how scents can impact mood, physiology, and emotions. I even provided the references on how smell is being used as an indicator of longevity, Alzheimer’s disease, and Parkinson’s disease. Most likely, these connections are based on neural connections and the role of “sniffing out danger” for species survival.
I also reviewed the evidence that odor receptors exist throughout the body, indicating that odorants have functions beyond their direct aromatic effects. This means, even if one suffers from loss of smell (anosmia), they could still benefit from secondary metabolites of essential oils that effect cellular and organ function. (You can read more about that here.)
Now, we add to smell its connection to appetite and food intake.
The Taste of Food Preference
In a previous blog, I discussed the health impacts of taste and how it was interrelated for survival as well. For example, taste receptors in the lungs have been found to respond to bitter tastes, possibly acting as a protective mechanism for bronchodilation if poison was ingested. Interestingly, genetics determine if we can taste certain properties of foods. Some people can taste bitter more than others due to a genetic variant. So, if you hate leafy green veggies, it could be that nature wanted your genetics to survive, as bitter is also the “taste of poison.” Or, it could mean that you were more susceptible to harm?!
There have also been links between receptors on our tongue to our gut, bringing in the connection of our favorite topic, the belly bugs. One study in Flavour states:
Oral sensing seems to mainly influence food discrimination and nutrient appetite, while post-oral chemosensors may relate to nutrient utilization and inhibition of appetite. The most common accepted view is that taste GPCRs are present in enteroendocrine cells among others also known as chemosensory cells.
Therefore, the sense of taste isn’t just influencing our food preferences and appetite, but utilization of nutrients in our bellies. This means if we can affect taste, we may impact digestion and appetite.
In a study with 103 patients that experienced Roux-en-Y gastric bypass surgery, it was found that changes in appetite, taste, and smell were noted by 97, 73 and 42% of patients, respectively. This study suggests a link between all three factors and demonstrates the connection to the physiology of the gut.
More on the Smell-Taste Link
A 2008 article in Live Science:
“The sensation of flavor is actually a combination of taste and smell,” said Tom Finger, a professor at the University of Colorado-Denver Medical School and chairman of the 2008 International Symposium on Olfaction and Taste, held last month in San Francisco. “If you hold your nose and start chewing a jelly bean taste is limited, but open your nose midway through chewing and then you suddenly recognize apple or watermelon.”
That’s because as you chew, you’re forcing air through your nasal passages, carrying the smell of the food along with it. Without that interplay of taste and smell, you wouldn’t be able to grasp complex flavors, Finger said. Instead you’d be limited to the basic taste sensations picked up chemically by the tongue: salty, sour, sweet, bitter and umami — a savory sensation frequently associated with the additive MSG. (Interestingly, this article predicted the link between smell and memory, which I just discussed above was confirmed recently.)
The Smell-Taste-Appetite Link
In a 2003 review study on the effect of sensory perception of foods on appetite and food intake, it was reported that palatability of food was linked to the sensory properties of taste, smell, texture, temperature, visual appearance, sound, and trigeminal input (irritative sensations). Interesting, the authors reported that one study did not show an effect of smelling an aroma on food consumption and hunger ratings, if the subjects weren’t hungry to start. However, pre-exposure to the sight of pizza and obviously, hunger ratings, did impact consumption. Other studies have reported a connection.
The differences of results could be explained by subject characteristics, that certain smells are more specific to evoke hunger cues, and smells can serve different functions. Furthermore, the authors stated that, “Taste and olfactory sensory-specific satiety can be produced by chewing samples of a food or by smelling the food for approximately as long as it would be in the mouth during a meal.” So, duration of the smell may be a factor as well.
Here’s another interesting question, “if smell can or can’t increase hunger, can hunger increase smell?”
A reverse relationship has been shown between the two. Specifically, hunger has been linked to an increase in our sense of smell and ingestion of food. Therefore, modulating smell could impact food intake, as the savvy researchers above demonstrated.
What’s the mechanism?
One rodent study in Nature Neuroscience found that presence of the cannabinoid type-1 (CB1) receptor in the olfactory bulb could be responsible… when little creatures were in fasting states. Specifically, endogenous endocannabinoids or exogenous cannabinoids (such as those in marijuana) can bind to the CB1 receptor activating hunger. A previous study in PNAS reported a similar effect with circulating levels of endogenous endocannabinoids linked to lower leptin levels (the “full hormone”).
This connection to production of these compounds and the biochemical feedback has been implicated in eating disorders. The Journal of Endocrinology Investigation explains as follows (geek-alert!):
Endocannabinoids are endogenous substances capable of binding to and functionally activating the two types of cannabinoid receptors identified to date, the cannabinoid receptors type 1 and 2 (CB1 and CB2 receptors)…
CB1 receptor and tissue concentrations of endocannabinoids sufficient to activate them are more widely distributed than originally believed, and are present in all brain and peripheral organs involved in the control of energy homeostasis, including the hypothalamus, nucleus accumbens, brainstem, vagus nerve, gastrointestinal trad, adipose tissue, muscle and liver.
Hypothalamic and peripheral neuropeptides and hormones involved in energy balance, as well as the type of diet, regulate endocannabinoid biosynthetic and inactivating pathways, whereas endocannabinoids, in turn, regulate the expression and action of mediators involved in nutrient intake and processing. The perturbation of these cross-talks might contribute to the development of eating disorders.
Aroma and Weight
So, it appears that smell, and the process of sniffing itself, has some evidence of effecting appetite. Now, what about directly impacting weight?
One study in Flavour with 10 individuals found that aroma impacted bite size, “Results for ten subjects (four females and six males), aged between 26 and 50 years, indicated that aroma intensity affected the size of the corresponding bite as well as that of subsequent bites. Higher aroma intensities resulted in significantly smaller sizes.” This could have a role in weight reduction.
In an earlier (somewhat controversial) large study of 3193 subjects, predominately females, it was found that inhaling certain aromas three times a day when feeling hungry did result in weight loss. The researchers found several connections to success in losing pounds in relationship to sniffing smells. Specifically, subjects who used the inhalers frequently, ate 2-4 meals a day, felt bad about overeating, but did not hate themselves, lost about 5% of their body weight a month. Interestingly, other correlations of psychological and food preferences (liking chocolate) also influenced outcomes.
Essential Oils and Aroma for Weight? What’s the Evidence?
A rodent study in Neuroscience Letter reported on a mechanism found in grapefruit oil and its potential link to weight loss. The authors stated in their conculsion, “Thus, the scent of grapefruit oil, and particularly its primary component limonene, affects autonomic nerves, enhances lipolysis through a histaminergic response, and reduces appetite and body weight.” I wrote previously on how secondary metabolites can modulate biochemical responses, such as inflammation and blood sugar.
Essential oils effect our physiology, emotions, and biochemistry. If you peer through my essential oils database, you can see all the roles essential oils have on our health and how some of these aspects were listed as factors in weight maintenance. Add this with some of the evidence of the impact of smell on appetite, and you can see where some bloggers are touting their potential for weight loss support.
I’d love to see more human studies specifically using essential oils, such as the one above on smell, to see if even greater effects could be achieved. According to an interview from the Essential Oils Revolution 2 with host Dr. Eric Z, Kristen Draughon has collected many testimonials on essential oils for the use of modulating hunger and effecting weight changes. I know many of my clients feel that they are helpful in their overall programs for wellness, including the goal of supporting a healthy weight for them.
Share your thoughts below.
American Chemical Society. New device could help improve taste of foods low in fat, sugar and salt. Science Daily. August 22, 2016. https://www.sciencedaily.com/releases/2016/08/160822083242.htm
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A cannabinoid connection between smell and appetite. Nature Neuroscience. February 10, 2014. http://www.natureasia.com/en/research/highlight/9097
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Essential Oils Revolution 2 with host Dr. Eric Z. [Health Summit] The True Power Behind Essential Oils Testimonials. Presented by Kristen Draughon. August 22, 2016.