Losing Your Sense of Smell to Lose Weight

A friend who went through an intense treatment of chemotherapy two years ago is still unable to smell, and thereby taste, most foods. She was warned this might be a treatment side effect, and when it would disappear was unknowable.  She used to eat chocolate, any kind of chocolate, as long as it was chocolate. “I don’t eat chocolate anymore,” she told me. “It tastes funny.”

That chocolate tastes funny to her is more likely to be from a loss of a sense of smell than taste.  According to Nancy E. Rawson, Ph.D. who is on the staff at the Monell Chemical Senses Center, Philadelphia, and Scientific Advisor to the Anosmia Foundation, it is our sense of smell, our olfactory system that gives us our taste sensitivity.  When people loss this olfactory function, when they have anosmia, they may not be able to taste the difference between an orange and a piece of chocolate.

As she and others explain, our ability to taste is almost totally dependent on our ability to smell. Of course, we can detect the basic tastes: sweet, salty, sour, bitter and umami, a savory taste sometimes associated with the taste of protein, even if we lose our sense of smell. But smell is the conduit to taste; without it the tastes of most foods are unrecognizable. We have cells high inside the nose, the olfactory sensory neurons, that connect directly to the brain. When we smell coffee brewing or popcorn popping, the microscopic “odor” molecules released by the food stimulate these neurons, and they message the brain, which then identifies the odor for us. (Dogs are much better at this than humans.) Interestingly, the smells come in not only through our nose, but also through a neuronal path connecting the roof of the throat to the nose. So when we chew our food, odors are also released that are picked up by the olfactory sensory neurons and sent to the brain.

A stuffy nose makes us aware of how important smell is in tasting what we are eating, and influences how much we enjoy or reject a particular food (think smelly cheese). But although it is frustrating to be unable to taste food when we have a cold, we know that once our stuffy nose disappears, we will be able to smell and enjoy eating once again.

It is this aspect of eating, enjoying the taste of food brought about by our ability to smell it, that has spawned interest in preventing the dieter from doing so.  If the food is tasteless, might the dieter eat less? Would the dieter stop eating when full, rather than continue to eat beyond fullness because the food tastes so good? Would impulsive eating of freshly baked chocolate chip cookies or French fries be thwarted because, without their scent, they lose their irresistible taste?

Apparently this occurred among subjects participating in a study in which they wore a nasal insert designed to redirect airflow in the nose away from those sensory olfactory neurons that tell the brain what we are smelling. Dror Dicker, MD, Rabin Medical Center, Israel, at the European Congress of Obesity a few weeks ago, described the device called Noznoz. The 65 subjects who wore the device while following a calorie-controlled diet lost significant weight; they especially reduced their consumption of sweet foods. In a sense, they had a perpetually stuffed nose.

Although the use of a custom-fitted nose device to reduce food intake is new,  the link between loss of the olfactory sense and altered food intake is well known. (“Olfactory Dysfunction Is Associated with the Intake of Macronutrients in Korean Adults,” Kong, Il, Kim, So, Kim, Min-Su et al, PLoS One 2016 ;11: 0164495)  Food intake among more than 1300 participants who had olfactory dysfunction (or inability to smell) was altered, compared to those who did not have this problem. Protein intake was reduced among males, the intake of sweet foods among young women, and consumption of high-fat food among young and middle-aged women. How the loss of the sense of smell differentially affected what was eaten or rejected was not explained in the paper.

Loss of the ability to smell odors may be one of the unwelcome aspects of aging. (“Effects of aging on smell and taste,”  Boyce, J. and Shone, G., Postgrad Med J. 2006 Apr; 82(966): 239–241)  The effect of aging on the deterioration of the sense of smell is so prevalent that one wonders if there ought to be generational-based recipes; foods made for an older population might have ingredients such as vinegar or lemon that can be tasted without a good sense of smell. Boyce and Shone state that in a recent survey almost 65% of 80-97 year olds have an impaired sense of smell.  The effects can be far ranging from the addition of too much salt and other spices to food in order to taste it, to malnutrition. Just as the loss of the sense of smell affects food intake among a younger population and decreases their food intake, so too the very old may eat less indiscriminately. They not only might avoid sweet or fat-rich foods, but food in general, thus causing them to be at risk for malnutrition. This is especially worrisome if their food intake is not sufficient to provide essential nutrients like protein, vitamins and minerals.

Fortunately the NozNoz and other interventions like a nasal spray that numbs the nose to smells, do not permanently eradicate this important sense. Indeed, its greatest utility might be putting them on when passing by sources of enticing food odors like sausages and onions cooking at a street fair that might tempt one into eating. It remains to be seen whether weight will be regained when and if the dieter removes the nose plugs. And of course, they may be helpful in cleaning up after a baby or dog.

 

 

One thought on “Losing Your Sense of Smell to Lose Weight

  1. Apprentice

    Excellent post Dr. Wurtman! My inkling is that weight will be regained after Noznoz apparatus comes off. I like your alternative utilization of it. I sure could have used it when my children were little 🙂

    Reply

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