Do you remember broccoli-gate? President George H.W. Bush sparked domestic and international outrage with his disdain for the vegetable. Years later, during President Barack Obama’s tenure, broccoli even became embroiled in the health-care debate as a proxy for perceived government overreach.
Why did Bush hate broccoli, while Obama loved it? It may come down to their genetics. To some people, broccoli (and related plants in the genus Brassica like cabbage and mustard, as well as coffee and hoppy beer) taste intensely bitter. For others, it doesn’t.
It turns out there is a stretch of DNA on chromosome 7 that affects how we taste some of the bitter chemicals in broccoli. In biologist lingo, we say that the gene taste 2 receptor member 38 (abbreviated TAS2R38 or T2R38) codes for a protein, and that protein regulates our bitter-taste ability.
While everyone should have a TAS2R38 gene, we don’t all have the exact same version. The different versions are called alleles. Some alleles allow us to taste the bitter compounds; some don’t. Several alleles of this gene are found in Africa (recall that Obama’s father was a Kenyan Luo), but elsewhere there are only two main versions: one for “taster” and one for “nontaster”.
Whether you can taste broccoli bitterness depends on which alleles you have. You inherit half of your autosomal DNA from your mother and half from your father. They each gave you an allele of the TAS2R38 gene. If you got two nontaster alleles, Brassica foods probably don’t taste bitter to you. If you get two taster alleles, broccoli and friends might be less than appealing. And if you get one copy of each allele—one taster and one nontaster—you can taste the bitterness, but only moderately. Scientists call these three states nontasters, supertasters, and tasters, respectively.
I can only guess at the genetic makeups of Presidents Bush and Obama, but I’ll venture that Bush was a supertaster while Obama was not.
You don’t have to guess for yourself, though, because some of the DNA testing companies report your status. And even if they don’t report it, it’s hidden in your raw data file, where you can check it if you know what to look for.
There are three spots in the TAS2R38 gene that differ between the common taster and nontaster alleles. We call those spots SNPs (for single nucleotide polymorphisms), and we give them truly atrocious names like rs10246939, rs1726866, and rs713598. The taster allele has the nucleotides C, G, and G at those respective SNPs, while the nontaster allele has T, A, and C.
You can download your raw data file from your testing company and search it for those SNPs to determine your own status. Depending on the testing company and test version, the file should report two or three of the SNPs. Most people will only need to know their status at one, though, because the SNP triads usually go together.
Not coincidentally, the fact that C, G, and G almost always go together in one allele and T, A, and C almost always go together in the other forms the basis for statistical phasing. Statistical phasing is a computational way of improving DNA matching by inferring which SNPs are together on one chromosomal copy versus the other.
The proportion of the taster allele varies by population. 23andMe has a nifty graph showing how it varies among their customers.
What Does This Have to Do with Covid?
Scientists have known for a while that some taste genes also affect immune response. (Here’s a thought: Are they actually immune genes that affect taste response?) And as a recent scientific study suggests, the ability to taste this particular kind of bitterness may make you more resistant to covid.
The study, published by doctors in Baton Rouge, Louisiana, and Cairo, Egypt, looked at 1,935 healthy people with increased exposure to covid (e.g., health care workers, patients). The researchers gauged the bitter sensitivity of the subjects and tracked them over time. About a quarter of the subjects were nontasters, about half were tasters, and the remaining were supertasters.
After 3 months, 266 (≈14%) of the subjects had tested positive for the virus. Nontasters were about 10 times more likely to test positive and nearly 4 times more likely to be hospitalized. They were also sick for longer (24 days on average) than tasters (14 days) or supertasters (5 days).
Of course, TAS2R38 is not the only factor affecting our susceptibility to covid. Age, underlying health conditions, the degree of exposure, and other genetic factors all play a part. That’s why it’s essential to get vaccinated, regardless of your ability to taste bitterness.
Check Your Status
If you don’t have access to trait reports at 23andMe or AncestryDNA, you can check your TAS2R38 status by looking in your raw data file. Depending on which company you used and when you tested, your file may not include all three SNPs.
Once you download the file (instructions for obtaining it from AncestryDNA are here), open it in a text editor and use the search function to find the SNP names. Here’s what you’re looking for and how to interpret it.
Consider my 23andMe data. The columns are: SNP name, chromosome number (7), position, and my base calls. The files from other companies might look slightly different but will contain the same basic information.
rs10246939 7 141672604 CT rs1726866 7 141672705 AG rs713598 7 141673345 CG
Notice that for each SNP, I have two different base calls, CT for the first SNP, AG for the second, and CG for the third. That’s because I have one taster allele and one nontaster one. I’m a taster, but not a supertaster.
If you have TT, AA, and CC, you are a nontaster, and if you have CC, GG, and GG, you are a supertaster.
If you’ve tested multiple family members, you can sometimes even track the alleles through your tree. My father, for example, is a nontaster, so I know I inherited my nontaster allele from him and my taster allele from my mother. It turns out she’s a supertaster, and her brother is a taster. That tells me that both of their parents (my maternal grandparents) were either tasters or supertasters, and at least one of them was definitely a taster. My husband is a nontaster and so are both of our kids. (One hates broccoli anyway.)
Now, eat your vegetables!