The wonderful thing about science is that it unweaves the fabric of the living world, warp by weft, for our understanding. It explores the world and brings to light these tiny facts, nuggets of information, these hypotheses and theories that give you wonderful explanations for your everyday observations. This is one reason which makes neuroscience, neurophysiology, neuroanthropology and neuropsychology (basically all these multiple disciplines beginning with neuro, as you may have validly surmised by now) particularly attractive to me !
The reason I say this is because, on so many occasions, i have read through articles on these and similar subjects and found wonderful insights into our everyday observations. These random explorations (basically an activity I indulge in when I am unable to focus on the job that i should legitimately be doing) have helped me sustain my fascination with science despite having completed a PhD (A PhD, as many of the graduates will agree is genuinely a degree in philosophy because it truly teaches you to accept failures and be philosophical about them :)). Anyways, getting back to the subject on hand, the most recent article to have caught my fancy in such a quest, is my discovery of a beautiful explanation for a common complaint of many women or rather of many chefs in general. Ever so often I have heard many of my friends complain that they feel satiated by the mere process of cooking. So much so that their appetite almost vanishes for the food that they have painstakingly cooked. This is a very common observation and for some reason i had always associated it with the smell of food activating the brain's satiation and pleasure centers before the actual food was partaken. This was of course just meaningless conjecture on my part, unsupported by any background search or review.
But then in a recent issue of the major science journal - Cell, I found a beautiful explanation for the above phenomena amply supported by evidence and not merely speculation. This chain of evidence, as I found out later, extends from times much earlier than now and in fact, the subject of olfactory perception and the activation of specific regions in the brain has been under study for many years now.
As some of the careful observers would have noticed in their life too, it is true that olfactory and visual, sensory signals do indeed contribute to our sense of satiation after or during a meal. A small portion of great looking and smelling food in a restaurant is much more pleasurable because of the sheer presentation, smell and ambience (even though the taste may not be dramatically different from a local take out place)! The importance of the aromas and the visual appeal of food in augmenting gastronomic pleasure has been duly stressed for several centuries now by both connoisseurs and lay men/women like me. I make special attempts at making the food atleast look good if not taste great... :)
Interestingly, I also learnt of one of the last diet fads, called the sensa diet, on the above hypothesis that enhancing the smell of foods (by sprinkling fragrant crystals of flavors and scents) decreases calorie intake by boosting the satiation signals in our central nervous system.
So, the first question that arises is - is their any merit to this observation ? What is the role of smell in altering our mind state ? Can food aromas increase our satiety ? How does this work ?
My brief search on some relevant literature led me to this paper by a research group in Yale, published in 2005 and which laid the foundation for the more recent finding.
I did realize a few interesting things through a perfunctory perusal of this manuscript. Interestingly, an odor molecule may reach the olfactory epithelium via the nose (called as orthonasal olfaction in technical jargon) or the mouth (called as retronasal olfaction). A smell is perceived as coming from the outer world when sensed through the nose whereas when sensed retronasally, it is perceived as arising from the mouth. In fact this illusion is so strong that people routinely mistake retronasal olfaction for "taste". So much so that even though our tongue is only capable of recognizing a limited palette of tastes - sweet, sour, salty, savory and bitter, we often can discern more complex tastes - medicinal, pleasant, fruity, rotten etc etc. And these "tastes" that we often sense are actually a result of the odors being sensed retronasally. Pinching the nose while eating or drinking is a simple experiment that will demonstrate this point. In fact, pinching the nose while drinking something distasteful / medicinal is a common strategy adopted by many, especially when dealing with kids.
A wise man called Rozin, had also observed that "olfaction" is the only dual sensory modality that senses both objects in the external world and inside (mouth). Based on this he further proposed that the same olfactory stimulation / smell may be perceived and evaluated in two qualitatively different ways depending on whether it is referred to the mouth or the external world.
Exploring this possibility the authors in 2005, showed through careful and controlled experimentation that although the smells traveling through the orthonasal or the retronasal route lead to the same olfactory receptors, they activate distinct regions of the brain. By delivering the aroma of chocolate (along with other chemicals about which i am not discussing now but which did yield interesting results) through distinct tubes that utilized the two distinct modes of olfactory perception, they studied the effect of the aroma and the mode of delivery on the brain activity. Monitoring the brain activation through functional MRI (fMRI), they clearly show that orthonasal delivery of smells activated the amygdala (which is involved in reward anticipation) while the retronasal mode of delivery triggered the activation of the medial orbitofrontal cortex, which is implicated in initiating the pleasure response upon the receipt of the reward. This was thus suggestive of the fact that retronasal olfaction possibly contributed more to satiation than the orthonasal route.
It was to test this hypothesis that the second group of researchers began their study. They used a special Mass spectrometry technique to quantify the aromas generated in an individual's retronasal passage. In their study asking volunteers to eat as much as they want to feel satiated, the experimenters found that the individuals who released more retronasal odorants tended to consume fewer calories. However, intriguingly, the authors also found that the total concentration of aromas released from a given food varies significantly among individuals. This is something i fail to understand but it does suggest that the complexity of a food's odor is only one component contributing to the satiation signals in the brain.
I wonder if there is any research on the visual component of the food... !!!
Meanwhile, this study does give some ray of hope for the foodies battling with weight loss plans.... You can make food smell great and end up eating less but still having the same pleasure index !!! So one can binge without a cringe !!
Refernces:
Small, D.M., et al. (2005). Neuron 47, 593–605.
Ruijschop, R.M., et al. (2009). J. Agric. Food Chem. 57, 9888–9894.
PS - Now, it does make me wonder though... it must be a tough choice for a restaurateur... Should he cut down on the aromas and the appearance of the food, so that people order more or should he allow people greater pleasure and satiation so that they come back again ? Guess that's why better restaurants cut down on the portions size and make great looking/smelling/tasting stuff... they make you want to eat more and let you eat more too !!!
