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The bitter truth: We shouldn’t like coffee, but we do

Photo by Tina Guina on Unsplash
Coffee drinkers learn to associate caffeine’s unpleasant taste with its pleasant “buzz” of alertness, and thus will drink — and even enjoy — the substance anyway.

Have you had a cup (or two or three) of coffee this morning?

Most likely you have. According to a survey taken earlier this year, 64 percent of Americans over the age of 18 drink at least one cup of coffee daily.

Yet, given coffee’s bitter taste, our fondness for the beverage is, well, somewhat odd. Bitterness is, after all, an evolutionary tool that helps us avoid the consumption of harmful foods and other substances.

Yet it gets even odder than that. For, according to a study published late last week in the journal Scientific Reports, people with a genetic variant that makes them especially sensitive to caffeine — one of the bitter compounds in coffee — tend to drink more coffee than those without that variant.

“You’d expect that people who are particularly sensitive to the bitter taste of caffeine would drink less coffee,” said Marilyn Cornelis, the study’s senior author and an assistant professor of preventive medicine at Northwestern University, in a released statement. “The opposite results of our study suggest coffee consumers acquire a taste or an ability to detect caffeine due to the learned positive reinforcement (i.e. stimulation) elicited by caffeine.”

In other words, coffee drinkers learn to associate caffeine’s unpleasant taste with its pleasant “buzz” of alertness, and thus will drink — and even enjoy — the substance anyway.

Those people, do, however, tend to drink less caffeinated tea than individuals without the variant. But that finding may be explained by the fact that they are too busy consuming coffee, says Cornelis.

Two databases

To do their study, the researchers used an epidemiological technique known as “Mendelian randomization.”

“We knew from previous research that inherited factors play a role in the amount of coffee and tea a person drinks a day, and that the ability to digest caffeine plays an important role in the people’s consumption of caffeinated beverage,” writes Daniel Liang-Dar Hwang, one of the authors of the study and a postdoctoral researcher at the University of Queensland, in an article for The Conversation.

“But we didn’t know whether genes for bitter taste perception were involved in determining consumption of bitter-tasting beverages,” he adds. “Previous studies with small sample sizes reported no or inconsistent relationships.”

The researchers began with data from a large Australian study involving more than 1,700 twins and their siblings. It showed that three particular gene variants are associated with a trio of distinct bitter tastes: caffeine, quinine (also found in coffee, as well as in tonic water), and an artificially made substance called 6-n-propylthiouracil, or PROP (a molecule that has the same bitterness as Brussels sprouts, according to Hwang).

The researchers then analyzed data from more than 430,000 adults participating in UK Biobank, a large database set up in the U.K. to help that country’s health officials collect information about preventing, diagnosing and treating a wide range of diseases. They compared the participants’ genetic data (specifically, whether they had any of the gene variants associated with sensitivities to caffeine, quinine or PROP) with their self-reports of how much coffee, tea and alcohol they drank each day.

“Compared to an average person, we showed that people who carried the bitter taste [gene] receptor for caffeine were more likely to be heavy coffee drinkers, meaning they drank more than four cups of coffee a day,” writes Hwang. “Every extra copy of the bitter taste receptor gene [led] to a 20% higher chance of being a heavy coffee drinker. These ‘super-tasters’ of caffeine also drank less tea.”

“In contrast, people who carried the bitter taste receptors for quinine or PROP drank less coffee and more tea,” he adds. “Compared to an average person, every extra copy of the quinine or PROP receptor gene was linked with a 9% or 4% chance of being a heavy tea drinker (meaning they drank more than 5 cups of tea a day.”

The study also found that people who had the gene variant associated with a greater sensitivity to PROP tended to drink less alcohol, particularly red wine.

Not only a matter of genes

The study comes with caveats, of course. Most notably, it relied on the participants’ own reports about how often they drank different beverages. Such self-reports can be unreliable. Also, most of the study’s participants were of European ancestry. The findings may not be applicable to other demographics.

Still, the findings are in line with other research that has identified genetic reasons for certain taste preferences — for example, why some people find cilantro delicious, while others complain it tastes “like soap.”

But, as Hwang points out, we can’t blame all our dietary preferences on our genes.

“Even if as a child or right now you dislike the bitterness of coffee or tea, you may have noticed that your taste and dietary behaviour change over time as you grow,” he explains. “So, even if you carried the ‘wrong’ genes in terms of tasting bitter flavours, you could still learn to enjoy deliciously bitter-tasting foods and beverages.”

FMI:  You can read the study in full on the Scientific Reports website.

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Comments (7)

  1. Submitted by Roy Everson on 11/19/2018 - 10:30 am.

    Study, schmuddy. We love coffee because of the obvious reasons and it often tastes great. The Dark Ages defined Europe for hundreds of years. After coffee and tea came along the Enlightenment soon dawned. Not a coincidence. That’s why we like bitterness now. Wake up, researchers.

  2. Submitted by Alan Straka on 11/19/2018 - 12:39 pm.

    I don’t care for coffee-too bitter. I do drink a lot of tea, mostly iced, and I am puzzled as to why one would think it tastes bitter. I don’t taste any bitterness but perhaps I have become desensitized. Is that possible? Do coffee drinkers find coffee bitter or do they no longer taste the bitterness?

  3. Submitted by Ray Schoch on 11/19/2018 - 04:42 pm.

    There are reasons I loathe Brussels Sprouts that have nothing to do with “bitterness.” This just gives me one more reason to avoid them. I’ve always liked the aroma of freshly-ground coffee. It’s the taste I can’t stand. On the other hand, I drink tea all day long, every day – hot, cold, it makes no difference – but don’t care about its aroma, whether dry or after brewing.

  4. Submitted by Jeffrey Brenner on 11/19/2018 - 05:04 pm.

    Many people take cream and sugar in their coffee, which cuts down the bitter taste. However, I like my coffee black, I don’t find the taste of a cup of good coffee to be bitter. If the coffee is made from good beans, it is not bitter.

  5. Submitted by Connie Sullivan on 11/19/2018 - 05:29 pm.

    Why do we drink beer? Or lemonade? Or eat pickles and sauerkraut and any fermented anything?

    Why do so many Americans suddenly (within the past twenty years) think eating their fish raw is a Good Taste?

    We like bitter. And sour. And the frisson or the acquired taste of Raw. Sorry, researchers!

  6. Submitted by Marc Post on 11/20/2018 - 10:41 am.

    If your coffee is bitter, it is either garbage (what I call, dirt in a can) or you are making it wrong.

  7. Submitted by Karen Sandness on 11/20/2018 - 11:41 am.

    When I was a child, I thought coffee was the worst thing ever and couldn’t understand why grown-ups drank it. As a college student, I learned to tolerate it as a necessary evil, but then, as a graduate student, I spent a summer session in Hawaii and encountered pure Kona coffee for the first time. It was like going from black-and-white TV to color.

    From there, I went to do research in Japan, where gourmet coffee was already a thing, and you could buy individually brewed cups of your choice of freshly ground beans. (This was in the 1970s). Since then, I have been a fussy coffee drinker, because different varieties vary tremendously in aroma, flavor notes, and intensity of roasting.

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