Happiness and the Taste of Food
October 8, 2008
Food tastes better at some times than it does at other times. I’ve attributed this to the restaurant, the ingredients, the seasonings, the chef or even, the weather. I’ve never thought it had to do with my mood. Yet if Jan Melichar is right the difference may be in my head and not in the food. Back in 2006 writing in the Journal of Neuroscience, he and his colleague Lucy Donaldson reported that taste perception changes with changing levels of the neurotransmitters, serotonin and noradrenaline. They were able to, “show for the first time that human taste thresholds are plastic and are lowered by modulation of systemic monoamines.”
Let me explain what this means. They gave people small amounts of very dilute flavors, not quite homeopathic but almost, on their tongues and asked if they could taste it. They diluted the flavors to the point that there was no taste perceived. Then they gave their test subjects a dose of a drug that upped their neurotransmitter levels. When they gave a selective serotonin-reuptake inhibitor like Prozac, the people were then able to discern the weak sweet and bitter tastes that previously they were unaware of. If they gave drugs that increased noradrenaline, the people were able to taste the dilute bitter and sour flavors that they were previously couldn’t.
This past July Melichar and Donaldson announced plans for a new study. They want to figure out if this decrease in taste perception consistently occurs when people are depressed. To find a reliable source of depressed people they are performing their study in conjunction with a study on Hepatitis C patients undergoing treatment with a drug called pegylated interferon. This drug causes severe depression in about 20% to 30% of patients who take it.
If these results pan out, this will present us with some interesting possibilities. Obviously the drug companies will love a quick, safe and cheap method to figure out who will respond to the antidepressant chemicals they market. These kinds of drugs are slow acting, it takes weeks of use to see a response. Think of the simple test that could be developed with this info, almost a litmus test to see who will feel better taking an SSRI. I can imagine the advertisements already. Remember the Pepsi Challenge advertising campaign? This could be a sales pitch even more effective than the multi-level-marketing company that tests beta-carotene in the skin to assess their antioxidant status.
Of course such a tool could be used to predict the benefit of other interventions as well. The idea that we might be able to assess our treatments quickly and safely is valuable for any type of treatment.
If taste is consistently blunted in depressed people, this will give us a method to even tell whether someone is even depressed. It’s often hard to know if someone is depressed Something or whether their apparent mental affect is the result of anemia, sleep deprivation or hypothyroidism.
Forgetting the clinical implications for a moment, perhaps this offers us a way to catalogue our memories. If you think of Thanksgiving dinners in years past and ask yourself how good the cranberry sauce tasted, you might be able to figure which years you were happy and which you were sad. Of course I’m told by my family that not everyone remembers the taste of food the way I do.
Could this explain why some people crave sweets when they are depressed? Perhaps their sweet taste perception is dulled and they never get enough ‘sweetness’ to reach satiety?
These thoughts about food come as the sun is about to set and we begin our celebration of Yom Kippur.
Does fasting change taste perception? One would assume that hunger sharpens taste perception. The research doesn’t seem to support this idea. A January 2006 paper in the journal Appetitie (yes, there really is a journal by that name), tested taste perception in hungry and fed students and could find no change. The obvious critique though was perhaps they weren’t hungry enough.
While the scientists and the drug companies research all this, I am happy to contemplate the simple knowledge that food tastes better in the company of good friends.
J Neurosci. 2006 Dec 6;26(49):12664-71.
Human taste thresholds are modulated by serotonin and noradrenaline.
Heath TP, Melichar JK, Nutt DJ, Donaldson LF.
Department of Physiology, University of Bristol, Bristol BS8 1TD, United Kingdom.
Circumstances in which serotonin (5-HT) and noradrenaline (NA) are altered, such as in anxiety or depression, are associated with taste disturbances, indicating the importance of these transmitters in the determination of taste thresholds in health and disease. In this study, we show for the first time that human taste thresholds are plastic and are lowered by modulation of systemic monoamines. Measurement of taste function in healthy humans before and after a 5-HT reuptake inhibitor, NA reuptake inhibitor, or placebo showed that enhancing 5-HT significantly reduced the sucrose taste threshold by 27% and the quinine taste threshold by 53%. In contrast, enhancing NA significantly reduced bitter taste threshold by 39% and sour threshold by 22%. In addition, the anxiety level was positively correlated with bitter and salt taste thresholds. We show that 5-HT and NA participate in setting taste thresholds, that human taste in normal healthy subjects is plastic, and that modulation of these neurotransmitters has distinct effects on different taste modalities. We present a model to explain these findings. In addition, we show that the general anxiety level is directly related to taste perception, suggesting that altered taste and appetite seen in affective disorders may reflect an actual change in the gustatory system.
Appetite. 2006 Jan;46(1):63-6. Epub 2005 Nov 17.
Relationship between taste thresholds and hunger under debate.
Pasquet P, Monneuse MO, Simmen B, Marez A, Hladik CM.
Centre National de la Recherche Scientifique UMR 5145: Eco-Anthropologie et Ethnobiologie, Musée de l'Homme, 17 place du Trocadéro, 75116 Paris, France. firstname.lastname@example.org
We determined taste recognition thresholds for six compounds (sucrose, fructose, sodium chloride, quinine sulphate, PROP and liquorice) in fasting students and, in the same subjects, after a meal. The testing procedure was the staircase-method in blind conditions. Although taste sensitivity may vary with hormonal status, our results did not show any significant difference in taste recognition thresholds between hunger and satiety. Our Bayesian analysis did not corroborate the hypothesis of increased sensitivity to nutrition-related tastants in the fasting state that was recently supported by data obtained with the two-alternative forced-choice method.