Taste Receptors: Bitter, sweet, and much more

Ever wonder why some people don’t like Brussel sprouts or strong, dark coffee?  Some people love a good, dark roast, cup of coffee – and Brussel sprouts and cabbage taste just great.

It turns out there is a lot of variation in the way people perceive different tastes.  For example: I can detect stevia in just about anything you try to hide it in — it has a terrible after taste to me.  I’ve tried multiple brands, and they are all terrible! But friends claim that stevia is just great and use it in everything. It turns out that I am genetically more sensitive to the bitter taste of steviol, which a lot of people can’t detect.

Taste Receptors: More than just liking different foods

If you are old enough, you probably remember the Life cereal commercials with Mikey, where the ultimate, picky taste test is whether “Mikey likes it!”

It turns out that we all taste things differently. There are multiple receptors that add to our perception of taste, and a lot of genetic diversity in those receptor genes.

So why is it an advantage to have differences in our taste receptors?  Having part of the community able to taste a bitter toxin and warn of the danger is vital. But, it is also important to having others who scarf down Brussels sprouts to let the community as a whole know that a bitter, but healthy, food is good to eat.

Here’s an example: One of the substances that some people can detect, at extremely low concentrations, is aristolochic acid, a toxin found in certain plant seeds.  In Eastern Europe, the plant tends to grow as a weed in fields, contaminating crops and causing kidney disease in those who ate the toxin. There is a 50-fold difference in people’s ability to taste aristolochic acid, although researchers are still trying to untangle the effects of taste ability vs the effect of the sensitivity of the gastrointestinal receptors on the disease-causing aspects of the toxin.

A lot of our biology is centered around food. Our brain controls our appetite, driving us to go out and obtain food (either through going to get take-out or physically hunting and gathering :-) Our body is formed to put us at the top of the food chain, able to hunt down animals and work the fields in agriculture.

Key to survival, our taste buds are essential for knowing whether food contains the nutrients that our body needs – and whether it is safe to eat. We instinctively know that a ripe strawberry is delicious, but a slightly over-ripe strawberry that is starting to decay a bit (bacteria, mold) is disgusting.

How do taste receptors work?

We all learned in early in our education that we have taste buds on our tongue to tell us about sweet, bitter, sour, salty, and umami (savory)flavors.

The cells that make up our taste buds abundantly produce taste receptors on the surface of the cells. These receptors bind to specific molecules from foods and send a signal to the brain – signaling for sweet or bitter as well as indicating intensity of the flavor. [ref]

The sweet and umami tastes are encoded in three genes in humans – and most animals. It turns out that a lot of animals are attracted to sweet tastes, indicating an easy source of energy. [ref]

There are a number of different genes that encode bitter taste receptors — and there are quite a few different molecules that we humans detect as being bitter.

Salty tastes are detected by receptors known as epithelial sodium channels. These are receptors that are sensitive to ions and can detect the different concentrations. Salty tastes aren’t just limited to table salt (sodium chloride), other molecules such as lithium choloride and potassium chloride also taste salty. [ref]

The image below (Creative Commons License) represents the different receptors available on taste buds for sweet, umami, bitter, and salty. [ref]

Taste receptors on a taste bud. Creative Commons Image license.

 

Taste receptor variants and food choices:

Unsurprisingly, people tend to eat more of the foods that they like and less of the food that they don’t like. (Yes, lots of research money spent to figure out what every parent knows.)

The heritability, or genetic component, of food preference is around 50% for most types of foods. The other half of the equation is all the rest of the variables – which foods were introduced to kids, when they were introduced, cultural habits, psychological factors, etc. [ref]

Hormones change your perception and desire for certain foods. The endocannabinoinds (and cannabinoids) increase your sensitivity to sweets, while leptin (full signal) decreases your taste for sweets. Ghrelin, the hunger hormone, increases your taste for salty and sour foods. [ref]

Taste receptors aren’t limited to the mouth

The taste receptors are just that – a receptor for a specific type of molecule. When in the mouth, located on a taste bud, it causes a signal to the brain of ‘bitter’ or ‘sweet’. But that same receptor can trigger other events events to happen if they are located in other cells.

Basically, the taste receptors work kind of like a lock and key. A specific chemical comes along that can bind only to a specific receptor on the surface of a cell. That binding or activation then triggers an action to happen within the cell.

Taste receptors are expressed on chemoreceptive epithelial cells throughout the respiratory and intestinal tract. These receptors don’t trigger a ‘taste’ sensation to be sent to the brain. Instead, they trigger a variety of other reactions to happen.

For example, in the sinuses, one of the bitter taste receptors is triggered by certain bacterial byproducts, causing a production of nitric oxide and the movement of nose cilia. This helps to kill that specific bacteria and move it out. (article on chronic sinus infections)  In other cells in your nose, sweet taste receptors also are activated by certain bacterial products. These sweet receptors decrease the immune response, and are linked to effects from commensal bacterial.[ref]

Taste receptors are also found in cells throughout the body including pancreas, bladder, thyroid, liver, brain, and testes. Yep, taste receptors in sperm… [ref]

What are all of the receptors doing? Well, let’s take the sweet taste receptors in the bladder as an example. It turns out that the reason that artificial sweeteners, such as saccharine, make some people feel like peeing more is due to sweet taste receptors in the bladder causing it to contract. [ref]

There are bitter taste receptors that are important in the thyroid gland and bitter taste receptor variants influence the risk of thyroid cancer. [ref] Similarly, researchers have found that certain bitter taste receptors are downregulated in breast cancer tissue. These are the same receptors that are associated with bitter compounds, such as bitter melon extract and chloroquinine, which inhibit tumor growth in breast cancer cells. [ref]

I can’t leave you dangling without explaining taste receptors in the testes…  It turns out that there are taste receptors for umami tastes in the sperm, and they affect male fertility (in animal studies). There are also bitter taste receptors in the testes and in sperm. A recent study showed that about 80% of sperm have measurable bitter taste receptors – and that there is a great variety of which ones are expressed in the sperm. Other research indicated that the taste receptors may be important in the sperm cilia motility.  [ref] [ref]

We all know that we taste food in our mouth, but it turns out that these same receptors are also found in the gastrointestinal tract, in the airways, and in the urinary tract. New studies are coming out all the time on the various functions that these ‘taste’ receptors perform in the body.[ref][ref]

Genetic Variants in the Taste Receptors

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TheTAS2R gene family, containing 43 different genes, is responsible for various bitter taste receptors, while the TAS1R family (just two genes) is responsible for sweet and umami tastes.

Salty and sour taste receptors are still being sorted out, and it turns out we also have taste receptors for fat.

Bitter taste receptors:

TAS2R38 gene: codes for the receptor that is linked to the taste of bitter in broccoli, Brussels sprouts, cabbage, watercress, chard, ethanol, and PROP. [ref][ref]  Interestingly, this taste receptor is also being studied as a target for type 2 diabetes medicines and is involved in triggering the production of bile acids.

Check your genetic data for rs713598 (23andMe v.4, v.5; AncestryDNA):

  • G/G: Can taste bitter in broccoli, etc.
  • C/G: Probably can taste bitter
  • C/C: Probably unable to taste some bitter flavors

Members: Your genotype for rs713598 is .

Check your genetic data for rs10246939 (23andMe v.4 and v.5; AncestryDNA)

  • C/C: Can taste bitter in broccoli, etc.
  • C/T: Probably can taste bitter
  • T/T: Probably unable to taste some bitter flavors

Members: Your genotype for rs10246939 is .

 

TAS2R16 gene: codes for the receptor that is associated with the taste of beta-glycorpyranoside [clinvar], which is in ethanol, bearberry, bacteria in spoilt or fermented foods, and willow bark (salicin).  [ref]

Studies on these variants look at the link between TAS2R16 gene variants and colon cancer, pursuing the idea that either a variation in vegetable intake would affect cancer risk. Another theory is that the variation in the amount of natural salicin compounds eaten would affect colon cancer risk (aspirin being preventative in colon cancer for some). The studies done so far though haven’t been able to make that connection. [ref]

Check your genetic data for rs846672 (23andMe v.4):

  • C/C: Can taste bitter in ethanol, fermented foods, etc
  • A/C: Probably can taste bitter
  • A/A: Probably unable to taste some bitter flavors

Members: Your genotype for rs846672 is .

Check your genetic data for rs846664 (23andMe v.5; AncestryDNA):

  • A/A: Can taste bitter in ethanol, fermented foods, etc
  • A/C: Probably can taste bitter
  • C/C: less able to taste some bitter flavors

Members: Your genotype for rs846664 is .

Check your genetic data for rs978739 (23andMe v.4 and v.5):

  • T/T: Can taste bitter in ethanol, fermented foods, etc
  • C/T: Probably can taste bitter
  • C/C: less able to taste some bitter flavors

Members: Your genotype for rs978739 is .

 

TAS2R19 gene: which is linked to the taste of quinine,  the bitter taste of grapefruit and tonic water. [study]

Check your genetic data for rs10772420 (23andMe v.5; AncestryDNA):

  • A/A: Can taste bitter in quinine
  • A/G: Probably can taste bitter in quinine
  • G/G: Less able to taste bitter in quinine

Members: Your genotype for rs10772420 is .

TAS2R4 gene: bitter taste receptor that responds to stevia, chloroquine, PTC, and denotonium benzoate. (Receptor is also found

Check your genetic data for rs2234001 (AncestryDNA):

  • GG: bitter taste for stevia
  • C/G: mix of bitter vs sweet tasters
  • C/C: sweet taste for stevia [ref], part of a haplotype associated with reduced thyroid cancer risk.[ref]

Members: Your genotype for rs2234001 is .


TAS2R14 gene: bitter taste receptor — stevia, absinthe, aristolochic acid, fishberries, and Hoodia Gordonii.[ref] [ref]

Of those who can taste bitter in stevia (from TAS2R4 above), some have a much strong perception of the bitter taste based on the TAS2R14 rs3741843 variant. [ref]

Check your genetic data for rs3741843 (23andMe v.4 ; AncestryDNA):

  • T/T: Lower sensitivity to bitter taste from stevia; better sperm motility
  • C/T: Stevia tastes more bitter (if able to taste the bitter); better sperm motility
  • C/C: Stevia tastes more bitter (if able to taste the bitter)[ref]; decrease sperm motility [ref]

Members: Your genotype for rs3741843 is .

Sweet and Umami Taste Receptors:

TAS1R3 gene: codes for a sweet taste receptor for which variations are estimated to produce about a 16% difference in variability of sweet taste perception.  This receptor also plays a role in umami taste as well, along with another gene. [ref] Umami, or savory flavors, are due to the detection of l-glutamate in foods.

One study found an increase in kid’s cavities linked to those who have a decreased sensitivity to the taste of sugar, perhaps due to eating more sugar to reach the same perception as those without the variant.  Scientists are still sorting out the reason why and how the change in the taste receptor protein is also altering insulin secretion.  [ref]

Check your genetic data for rs35744813 (23andMe v.4 ):

  • T/T: Decreased taste sensitivity for sucrose
  • C/T: Somewhat decreased taste sensitivity for sucrose
  • C/C: Normal taste receptor for sucrose

Members: Your genotype for rs35744813 is .

Check your genetic data for rs307355 (23andMe v.5 only):

  • T/T: Decreased taste sensitivity for sucrose
  • C/T: Somewhat decreased taste
  • C/C: Normal taste sensitivity for sucrose

Members: Your genotype for rs307355 is .

Salty taste receptors:

SCNN1A gene: codes for a salt sensitive receptor. These receptors are found in our salt taste receptors as well as elsewhere in the body. Genetically, some are linked with being more or less likely to have blood pressure that is sensitive to the amount of salt in the diet.

Check your genetic data for rs11614164 (AncestryDNA):

  • A/A: typical
  • A/G: blood pressure less likely to be salt-sensitive
  • G/G:  blood pressure less likely to be salt-sensitive[ref]

Members: Your genotype for rs11614164 is .

 


Lifehacks:

 

Your gut knows the difference between sugar and artificial sweeteners. While both may taste sweet and signal ‘sweet’ to the brain, receptors in the gut respond via that vagus nerve to real sugar – and don’t respond to artificial sweeteners. Basically, the gut is giving a positive feedback to the brain when sugar is ingested. [ref]

Zinc is integral to our ability to taste. When it comes to the ability to taste salt, a deficiency in zinc can cause you to eat more salt. [ref]

GABA, an amino acid, blocks the TAS2R4 taste receptor, which is the receptor for quinine. [ref]

Hacking pre-diabetes? Glucagon-like peptide 1 is a hormone that increases insulin secretion with suppressing glucagon secretion. It is a target of a lot of anti-diabetes research. The TAS2R38 gene is located on the same cells in the gastrointestinal tract as glucagon-like peptide 1 cells. Recent research shows that bitter substances that activate TAS2R38 can also increase glucagon-like peptide 1 release.[ref]  One such substance is berberine. [ref]

Want to experiment with the way things taste? Try using a saline nose rinse or neti pot with a little salt – before and after having a few sips of your morning coffee…

 



Author Information:   Debbie Moon
Debbie Moon is the founder of Genetic Lifehacks. She holds a Master of Science in Biological Sciences from Clemson University. Debbie is a science communicator who is passionate about explaining evidence-based health information. Her goal with Genetic Lifehacks is to bridge the gap between scientific research and the lay person's ability to utilize that information. To contact Debbie, visit the contact page.