Genes are fundamental units of heredity, carrying instructions that determine various traits and functions. Among these, the TAS2R38 gene plays a role in how individuals experience taste, influencing how certain compounds are detected and interpreted by the brain. Understanding this gene offers insights into the biological mechanisms underlying human sensory experiences.
The Gene for Bitter Taste
The TAS2R38 gene encodes a bitter taste receptor protein, located primarily in taste cells within the oral cavity. This receptor is part of a larger family of G protein-coupled receptors (GPCRs) that detect various bitter chemicals. Its function involves recognizing and binding to particular bitter compounds, notably thiourea compounds such as phenylthiocarbamide (PTC) and 6-n-propylthiouracil (PROP). These compounds are used in research to study bitter taste.
When PTC or PROP molecules bind to the TAS2R38 receptor, a signal transduction pathway is initiated. This process begins with the activation of the G protein, which triggers a cascade of intracellular events leading to the release of calcium ions within the taste cell. This rise in intracellular calcium generates a nerve impulse, which is transmitted to the brain, resulting in the perception of a bitter taste. Beyond the oral cavity, TAS2R38 receptors are also found in other areas like the gastrointestinal tract and lungs, and have been implicated in detecting bacterial compounds, suggesting broader physiological roles beyond taste.
Why People Taste Bitterness Differently
Individual differences in bitter taste perception are attributed to genetic variations, or alleles, of the TAS2R38 gene. There are two common functional variants of the TAS2R38 protein: PAV and AVI. The PAV variant is associated with a functional receptor sensitive to bitter compounds like PTC and PROP, while the AVI variant is non-functional, leading to reduced sensitivity. These variations arise from three single nucleotide polymorphisms (SNPs) within the gene, which are strongly linked in most populations.
People inherit two copies of the TAS2R38 gene, one from each parent, leading to different combinations of these alleles. Individuals with two copies of the PAV allele (PAV/PAV genotype) are called “tasters” or “supertasters” because they perceive bitter compounds with high intensity. Those with two copies of the AVI allele (AVI/AVI genotype) are “non-tasters,” experiencing little bitterness from these compounds. Individuals with one PAV and one AVI allele (PAV/AVI genotype) are “medium tasters,” with intermediate bitter taste sensitivity. Genotype frequencies vary across populations, with distributions often around 32% PAV/PAV, 44% PAV/AVI, and 24% AVI/AVI.
How Taste Perception Influences Health
TAS2R38 genetic variations, which affect bitter taste perception, can influence food preferences and dietary habits. For example, individuals with the PAV/PAV genotype, highly sensitive to bitterness, may avoid bitter vegetables like broccoli, Brussels sprouts, or kale, which contain bitter glucosinolates. This aversion can lead to lower consumption of these nutrient-rich foods, impacting their intake of beneficial vitamins, minerals, and phytonutrients.
Non-tasters (AVI/AVI genotype) may be more inclined to consume foods tasters find unpalatable due to bitterness. Research suggests non-tasters may have a higher intake of sweets and fats, which has been linked to a higher body mass index (BMI) or increased obesity risk in some populations. The TAS2R38 genetic variation has also been associated with diet quality, with differences in dietary patterns observed between genotypes, especially in obese individuals. Beyond food preferences, bitter taste receptors are also found in the gut, where they can influence the release of hormones involved in appetite regulation, further connecting taste perception to metabolic health.