NRSC 4132 Blog

When stressed, many people eat less, citing lack of time or simple forgetfulness as the reason they skip meals or eat less often when they have looming deadlines. What if, when stressed, people get less enjoyment out of their meals? Recent studies have shown that taste disturbances resulting from anxiety or depression may play a role in lower appetite. When we are anxious, we simply cannot taste food as well as we normally would.

Until the last 20 years or so, taste thresholds were thought to be invariable; genetics determined taste threshold, meaning people could range anywhere from a non-taster to a supertaster. Surprisingly, it has come to light that taste thresholds are far more plastic and variable than previously thought. In the first research studies on taste in depressed patients, it was found that depression resulted in decreased sensitivity to all tastes, but to sweet tastes in particular. Those with panic disorder and average people with induced stress tend to be more sensitive to bitter tastes. These taste disturbances seem to be linked to alterations in serotonin (5-HT) and noradrenaline (NA). 5-HT and NA alter ion channel function, resulting in a change in the excitability of taste cells. As a result of this research, in a 2006 study, Heath et al focused on 5-HT and NA in an attempt to determine the link between these monoamines, mood, and taste.

Heath et al studied taste responses to sweet, bitter, salt, or sour tastes in subjects who had no previous history of depression or anxiety and who were not using psychotrophic medication. Taste perception was measured before and after administration of a 5-HT reuptake inhibitor (SSRI, a common ingredient in antidepressant and anti-anxiety medications), a NA reuptake inhibitor (NARI, which treats depression), or a placebo (lactose). Findings indicated that SSRIs significantly increased bitter and sweet taste sensitivity (i.e. these taste thresholds were reduced), while NARIs increased bitter and sour taste sensitivities. Interestingly, neither drug affected salt taste.

So how exactly can SSRIs and NARIs modulate taste? In an earlier model, part of the mechanism was proposed, with additions by Heath et al. First, receptor cells release ATP (which can function as neurotransmitter) as a result of increased intracellular calcium. Next, ATP activates receptors on presynaptic cells, causing an increase of calcium in presynaptic cells, followed by 5-HT release. Heath et al further suggest that serotonergic feedback from presynaptic cells to receptor cells occurs. The 5-HT released from presynaptic cells binds to receptors on the receptor cells, exerting its effects by volume transmission. SSRI administration blocks 5-HT transporters on both receptor and presynaptic cells and enhances 5-HT signaling, and therefore enhances bitter and sweet tastes. On the other hand, NA can act either as a transmitter released onto gustatory afferent axons or by modulating the action of ATP.

In addition to taste perception due to monoamine manipulation, Heath et al studied the relationship between taste and mood. Although all subjects were in the clinically healthy range for Spielberger State and Trait questionnaire (which represent anxiety levels) and Beck's Depression Inventory, some subjects scored on the high range of the Spielberger Trait questionnaire, meaning that they had higher anxiety levels than the other subjects. The more anxious subjects had lower taste sensitivities to bitter and salt tastes. All patients scored very low on depression, so a relationship between depression and taste perception could not be determined. Since 5-HT or NA manipulations do not alter salt thresholds, this effect would need to be studied further.

The next time you get stressed out, think about whether your food seems to taste different than it normally does.

Main article: http://www.jneurosci.org/content/26/49/12664.full.pdf+html