Nobody at the table is tasting the same meal
Most arguments about food are treated as arguments about taste, in the sense of preference. A surprising number of them are arguments about perception, in the sense of hardware. The two people are not disagreeing about the same experience. They are having different ones.
Cilantro genuinely tastes of soap to some people
Cilantro produces a family of compounds called aldehydes. So do some soaps. That is not a coincidence of description, it is chemistry: the overlap is real, and whether you notice it depends on how sensitive your nose happens to be to those specific molecules.
A study of a large consumer genetics cohort found a variant sitting next to a cluster of smell-receptor genes on chromosome 11 associated with disliking cilantro. Among the genes in that cluster is one that responds strongly to exactly the aldehydes cilantro makes.
The rates differ by ancestry, and both numbers are worth stating rather than one. Around 12 to 14 percent of people with European or Ashkenazi Jewish ancestry report cilantro tasting soapy, compared with roughly 4 percent of people with South Asian ancestry, with other groups falling in between. So this is a minority experience everywhere, and a much larger minority in some places than others.
The effect of the variant itself is a lean, not a switch. Plenty of people carry it and eat cilantro happily, often because familiarity does a lot of work. But the people telling you it tastes like dish soap are not being difficult. They are describing what they smell.
Six in ten people cannot smell what asparagus does
Eating asparagus produces sulfur compounds that end up in urine. Essentially everyone produces them. Detecting them is another matter.
In a study of 6,909 people of European-American descent, 58 percent of men and 62 percent of women could not smell it at all. The remaining 42 and 38 percent could. The researchers linked the difference to hundreds of variants in a region of chromosome 1 dense with smell-receptor genes.
Which produces a nicely absurd situation: the majority of people have no idea this is happening, and a sizable minority has been wondering for years why nobody else mentions it.
Redheads need more anesthetic
Perception differences are not confined to smell, and not all of them are trivia.
In a study of women undergoing surgery, natural redheads required about 20 percent more of an inhaled anesthetic than dark-haired women to reach the same depth of anesthesia. In the published comparison the redheaded group needed 6.2 percent desflurane against 5.2 percent for the dark-haired group. Nine of the ten redheads carried variants in MC1R, the gene that produces red hair by changing a pigment receptor, and that receptor family also has connections to pain signaling.
This is a small study, and it should be read as one. But it has held up well enough to be worth a sentence to your anesthetist, who will very likely have heard it before.
Bitterness is the one you can watch happen at dinner
The most visible version of all this is bitter taste. A receptor called TAS2R38 detects certain bitter compounds found in broccoli, kale, and sprouts. Depending on which versions you inherited, the same compound registers as mildly bitter, aggressively bitter, or close to nothing.
Three people can share one dish and have three different experiences of it, none of which is available to the others. It is worth remembering the next time a child is accused of being dramatic about vegetables, and we cover the detail in the bitter taste article.
Why any of this matters beyond dinner party facts
Because perception is the one place where genetic variation is not abstract. Most common variants shift a probability you can never feel directly. These ones you can check tonight.
That makes them the clearest available demonstration of what a DNA report is actually for. Not to tell you who you are, but to point at the places where your equipment differs from the standard assumption, so you stop treating your own experience as the neutral one.
Your Helisoma report reads these markers, bitter taste and earwax type and the photic sneeze among them, out of the raw file from any major test. It is a good place to start, because you can immediately check the report against your own life and see whether it is telling the truth.
Sources
- Eriksson N, Wu S, Do CB, et al. A genetic variant near olfactory receptor genes influences cilantro preference. Flavour, 2012. doi:10.1186/2044-7248-1-22
- Markt SC, Nuttall E, Turman C, et al. Sniffing out significant "Pee values": genome wide association study of asparagus anosmia. BMJ, 2016. PubMed 27965198
- Liem EB, Lin CM, Suleman MI, et al. Anesthetic requirement is increased in redheads. Anesthesiology, 2004. PubMed 15277908