UAE scientist investigates whether depression is a matter of taste

Depression can be debilitating and it is widespread in the UAE. But new research suggests the key to an early diagnosis could literally be on the tip of your tongue.

Dr Justin Thomas, an Assistant Professor at Zayed University, has been studying depression among Emiratis for the past two years. Andrew Henderson / The National

Depression can be debilitating. And it is widespread in the UAE, with a recent study finding that as many as one in four Emirati students suffers from the condition.

But new research suggests the key to an early diagnosis could literally be on the tip of your tongue.

That is the finding of a team of Abu Dhabi researchers who have established a link between the genes that make our taste buds work and a condition that inhibits the ability to experience pleasure.

In a draft research paper recently submitted to the peer-review journal Psychiatry Research, Dr Justin Thomas, an assistant professor at Zayed University's department of natural science and public health, proposes that taste sensitivity represents an important and easily recognisable indicator of anhedonia - the failure to enjoy typically enjoyable things.

"It was a simple idea to explore: the idea that one of the differentiating symptoms of depression is anhedonia, or the diminished ability to experience pleasure," Dr Thomas explained. "With anhedonia, you're not sad, you just have a hard time feeling pleasure. Nothing quite gives you a buzz."

Dr Thomas hypothesised that "supertasters" - people with an unusually high density of taste buds - have a higher "hedonic capacity", or ability to experience pleasure.

"We thought supertasters, in general, are more globally pleasure-sensitive," Dr Thomas said. "Logically, that would make sense. If you're easy to please, you're less likely to suffer from depression."

For the study, which was supported by grants from the Emirates Foundation and the National Research Foundation, he and his team tested 198 male and female Emirati students attending Zayed University, giving them a common taste test - the bitter compound phenylthiocarbamide (PTC) on a 5-centimetre strip of blotting paper, which they placed on their tongues.

Depending on the subject's genetic makeup, the PTC tastes either flavourless, mildly bitter or intensely bitter.

"For those supertasters we tested, it's horrible, it's bitter, it's ugh!" Dr Thomas said. "They immediately go and get a drink of water.

"But then you have the non-tasters looking at the others like they're crazy, like 'What's wrong with you?' Some of them ask for another sample to try, thinking they must have got a dud. It's quite a fun thing to watch."

Subjects split into non-tasters, regular tasters, and supertasters. Regular tasters experience the PTC as barely detectable, with just a hint of bitterness.

Among the supertasters was Meera al Mutawa. To her, the PTC tasted so bitter to her she removed it immediately. "I was never able to drink coffee as I found it so bitter, and I used to envy people in coffee shops as they could order drinks with fancy names, and all I would drink is hot chocolate," she said.

"I would say I rarely get depressed. I'm a very cheerful, optimistic person, and if I'm feeling down, I would eat anything that I really like and instantly feel better."

Globally, about a quarter of the population are thought to be supertasters. Half are normal tasters, and the remaining quarter are classified as "non-tasters" - people who are likely to have a high tolerance for spicy foods or carbonated drinks.

Then they looked at the test group's capacity to experience pleasure, putting the students through a common psychiatric self-evaluation tool called the Snaith-Hamilton Pleasure Scale (Shaps).

The test - posed in English or Arabic - asks subjects to rate how much pleasure they get from everyday things like a cool breeze on a warm day or splashing in the sea, on a scale from one ("strongly disagree") up to four ("strongly agree"). It covers areas of interests and pastimes, social interaction, sensory experience, and food and drink.

And they found that the super-tasters had a greater "pleasure capacity score" than the non-tasters.

Non-tasters scored a mean value of 46.97 points - on a scale from 14 to 56 - compared with supertasters, who scored 48.88 points. Regular tasters were in the middle with 47.92 points.

That 1.9-point difference between the non-tasters and supertasters, while "modest", is still "statistically significant", the researchers concluded. "The finding that non-tasters had significantly lower hedonic capacity scores than supertasters is modestly supportive of a link between taste sensitivity and anhedonia."

Dr Thomas said the study represents the first attempt to directly explore the relationship between taste sensitivity and hedonic capacity.

"We use this term 'depression' as if it's one homogeneous illness. But it's already been split into subgroups," he said.

"Some people's depression is characterised by anhedonia, and we call that melancholic depression. For others, it's characterised by sadness, or dysphoria. Non-tasters are more anhedonic as they derive less pleasure from one of their senses."

But does this mean your foodie friends are less likely to be depressed? Not so fast, says Dr Thomas - the link between taste sensitivity and depression may only exist in diagnosed cases typified by anhedonia. "There are so many factors that contribute to depression."

Even so, there are potentially important implications for understanding vulnerability to depressive illnesses.

For one thing, determining taste sensitivity could be as simple as looking at a person's tongue to see the number of papillae, the tiny bumps indicating taste receptors.

"If you look at the tongue of a super-taster, it's visible to the eye - all those bumps, especially if you eat something with food colouring," he said. By contrast, the tongues of non-tasters look smoother.

But it could help with prescribing effective treatments sooner.

"With other indicators, this could be part of an at-risk screening process used in targeted prevention."