The Dinner Party Gene
At any dinner table, the same dish of roasted Brussels sprouts will taste completely different to different people. To roughly one quarter of diners, those sprouts are pleasantly mild and nutty. To another quarter, they are overwhelmingly, almost offensively bitter. The rest fall somewhere in between. The primary reason for this variation is genetic: a single bitter taste receptor gene called TAS2R38.
TAS2R38 was the first taste receptor gene linked to a specific perceptual difference in humans, and it remains the most dramatic example of genetic variation in taste. The ability to taste the compound PTC (phenylthiocarbamide) was actually discovered by accident in 1931, when chemist Arthur Fox noticed that his colleague found PTC powder intensely bitter while Fox himself tasted nothing at all.
The Genetics: PAV vs AVI
The TAS2R38 gene encodes a G-protein-coupled receptor on taste bud cells. Three non-synonymous SNPs alter the receptor's binding pocket, determining whether it can detect thiourea-containing compounds:
- rs713598 (position 49): C = Proline (P), G = Alanine (A)
- rs1726866 (position 262): C = Alanine (A), T = Valine (V)
- rs10246939 (position 296): C = Valine (V), T = Isoleucine (I)
These combine into two common haplotypes. The PAV (taster) haplotype produces a receptor that binds PTC and PROP tightly. The AVI (non-taster) haplotype produces a receptor with an altered binding pocket that essentially cannot detect these compounds.
Taster Phenotypes
- PAV/PAV (supertaster): Both copies produce functional receptors. PTC and PROP are perceived as extremely bitter. Cruciferous vegetables, dark leafy greens, black coffee, and tonic water may taste unpleasantly bitter. About 25% of people.
- PAV/AVI (medium taster): One functional and one non-functional copy. Moderate bitter perception. Can usually taste PTC but less intensely. About 50% of people.
- AVI/AVI (non-taster): No functional receptor. PTC and PROP are tasteless. Cruciferous vegetables taste milder. Tend to be more adventurous with bitter foods. About 25% of people.
What Supertasters Actually Experience
Supertasting goes beyond broccoli. PAV/PAV individuals tend to perceive a range of bitter compounds more intensely, and some research suggests they have a higher density of fungiform papillae (taste bud-containing structures) on the tongue. This affects their experience of many foods and beverages:
- Cruciferous vegetables (broccoli, Brussels sprouts, cauliflower, kale) taste more bitter due to glucosinolates like sinigrin and goitrin
- Black coffee and dark chocolate are perceived as more bitter
- Tonic water (quinine) is more unpleasant
- Grapefruit juice may taste more bitter due to naringin
- Some supertasters are more sensitive to capsaicin (chili heat) and ethanol burn
The Evolutionary Story
Why would natural selection maintain both taster and non-taster alleles at roughly equal frequency? The leading hypothesis involves a trade-off. In ancestral environments, the ability to detect bitter plant alkaloids was protective against ingesting toxins. Many poisonous plants produce bitter compounds as chemical defenses, and individuals who could taste them were less likely to eat something lethal.
However, many bitter-tasting plants are also highly nutritious. Cruciferous vegetables contain glucosinolates that are anticarcinogenic. Dark leafy greens are packed with vitamins and minerals. Non-tasters, by finding these foods palatable, may have had better nutrition in environments where toxic plants were rare. Balancing selection — where both alleles confer context-dependent advantages — may explain why non-tasters have not been eliminated from the gene pool.
Health Implications
TAS2R38 genotype has been linked to several health-relevant outcomes in epidemiological studies:
- Vegetable intake: Supertasters consume fewer cruciferous vegetables on average, which could reduce their intake of anticarcinogenic glucosinolates.
- Body weight: Some studies find supertasters tend to be leaner (possibly due to lower preference for high-fat, high-sugar foods), though results are mixed.
- Alcohol consumption: Supertasters report finding alcoholic beverages more bitter and may drink less.
- Sinus health: Intriguingly, TAS2R38 is also expressed in upper respiratory epithelium, where it detects bacterial compounds. The PAV (taster) haplotype triggers faster innate immune responses to certain pathogens, potentially reducing susceptibility to chronic rhinosinusitis.
The Fun Test
Before checking your genotype, you can try the classic taste test at home. PTC taste strips are available online for a few dollars. Place one on your tongue: if it tastes intensely bitter, you are likely PAV/PAV or PAV/AVI. If it tastes like plain paper, you are almost certainly AVI/AVI. For a more precise reading, look up all three SNPs.