Smell, Taste and Flavour
Most people are aware that smell and taste are closely linked. Indeed, a common question that people with anosmia are asked when telling someone about their condition is ‘so can’t you taste anything then?’. This is a fair question, on the face of it, but before asking or even answering it, one should consider what is actually meant by the word ‘taste’.
Taste and the Role of the Taste Buds in Humans
Strictly speaking, the word taste, or gustation, refers to what is sensed by the taste cells, located on the front and back of the tongue and on the sides, back and roof of the mouth. These cells, or taste buds, bind with molecules from food being eaten and send signals to the brain. The way our brains perceive these stimuli is what we refer to as taste, which can be broken down into five areas : salty, bitter, sweet, sour and umami.
If you think about it however, these five areas do not give a complete picture. Take mint, for example; our perception of mint cannot be readily assigned to one of the five categories above. There is, of course, a whole realm of sensation available to us beyond these five areas; this realm is what we call flavour, and much of this comes from our sense of smell.
Flavour and Smell
A great proportion of the overall flavour of food and drink is the result of the olfactory neurones at the top of our nasal cavity detecting molecules of the food we are eating. But how does this happen? We do of course detect the scent of the food in front of us as molecules from it pass into our nostrils, but most of the flavours we perceive come from within the mouth itself, via a process called retronasal olfaction.
This is a complicated-sounding name for molecules of whatever it is that we are eating travelling into the nasal cavity via the passage that connects it to the back of our throat. Why do wine tasters hold wine in their mouths and swill it around before spitting out? It is to encourage as much flavour as possible up into the nose to get a better sense of the bouquet of the wine.
So what does this mean if you have a smell disorder?
Bearing in mind what we have covered so far, one can imagine the effect that smell loss has on the ability to enjoy food. Much, if not all (depending on the degree of smell loss experienced by an individual) of the flavour within food is lost. A simple way for someone who has a fully functioning sense of smell to partially experience this for themselves is to hold their nose whilst eating. This demonstrates how this nose (and the ability to smell) has an affect on the flavour of the food. On Anosmia Awareness Day 2020, we visited the English National Opera and asked their CEO, Stuart Murphy to do this test. You can watch how this worked out here.
As a result, appetite doesn’t work in the same way; if you can’t smell dinner cooking in the oven then how do you look forward to eating it, and what stimulates the body to prepare to eat? Salivation very often occurs in response to food-related odours. Anosmia sufferers are left to rely on their bodies telling them that it is time to eat – that feeling of needing food, the sensation of ’emptiness’ – but this doesn’t always work. They can forget to eat, or simply do not feel hungry, and can run the risk of weight loss or malnutrition.